Network Working Group                                        J. Haluska
Internet Draft                                                Telcordia
Intended status: Informational                                 R. Ahern
Expires: April 2010                  AT&T Customer Information Services
                                                            P. Lum Lung
                                     Qwest Communications International
                                                           C. Blackwell
                                                                Verizon
                                                       October 23, 2009



    Considerations for Information Services and Operator Services Using
                                    SIP
             draft-haluska-sipping-directory-assistance-09.txt






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Abstract

   Information Services are services whereby information is provided in
   response to user requests, and may include involvement of a human or
   automated agent. A popular existing Information Service is Directory
   Assistance (DA). Moving ahead, Information Services providers
   envision exciting multimedia services that support simultaneous
   voice and data interactions with full operator backup at any time
   during the call. Information Services providers are planning to
   migrate to SIP based platforms, which will enable such advanced
   services, while continuing to support traditional DA services.

   Operator Services are traditional PSTN services which often involve
   providing human or automated assistance to a caller, and often
   require the specialized capabilities traditionally provided by an
   operator services switch. Market and/or regulatory factors in some
   jurisdictions dictate that some subset of Operator Services continue
   to be provided going forward.

   This document aims to identify how Operator and Information Services
   can be implemented using existing or currently proposed SIP
   mechanisms, to identity existing protocol gaps, and to provide a set
   of Best Current Practices to facilitate interoperability. For
   Operator Services, the intention is to describe how current operator
   services can continue to be provided to PSTN based subscribers via a
   SIP based operator services architecture. It also looks at how
   current operator services might be provided to SIP based subscribers
   via such an architecture, but does not consider the larger question


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   of the need for or usefulness or suitability of each of these
   services for SIP based subscribers.

Table of Contents


   1. Introduction...................................................4
   2. Protocol Gaps..................................................6
   3. Terminology....................................................7
   4. High Level Requirements.......................................10
      4.1. Potential Future Requirements............................12
   5. Information Services..........................................13
   6. Operator Services.............................................17
      6.1. Inter Provider Capabilities..............................19
      6.2. Inter OISP Capabilities..................................19
      6.3. Intra OISP Capabilities..................................20
      6.4. Capabilities Required for Specific Services..............21
   7. OISP Internal Architecture....................................22
   8. General Approach..............................................24
   9. Signaling Mechanisms..........................................26
      9.1. PSTN Protocol Interworking...............................26
      9.2. Conveying Application Specific Information...............27
      9.3. Calling Party's Identity.................................28
      9.4. Provider Identification..................................30
         9.4.1. Home Provider.......................................30
         9.4.2. Intermediate Provider...............................31
      9.5. Originating Line Information/ANI II Value................33
      9.6. Trunk Group Identifier...................................34
      9.7. Identification of PSTN Originated Calls..................36
      9.8. Dialed Digits............................................36
      9.9. Retargeting to Identify the Desired Service..............37
      9.10. Charge Number...........................................37
      9.11. Access Prefix...........................................38
      9.12. Signaling of Carrier Information........................39
      9.13. Transit Network Selection...............................41
      9.14. Carrier Identification..................................42
      9.15. Carrier Selection Information...........................42
      9.16. Passing Whisper.........................................43
      9.17. Calling Equipment Capabilities and Characteristics......46
      9.18. Media Server Returning Data to the Application Server...47
      9.19. Control of Cut Through Direction for PSTN Interworking..48
      9.20. With Holding of Final Responses.........................48
   10. Example Call Flow - Directory Assistance.....................49
      10.1. Basic Flow..............................................49
      10.2. OISP Drops Out at Call Completion Setup.................58
      10.3. OISP Drops Out After Call Completion Call is Answered...60
      10.4. OISP Drops Out After Interaction with Called Party......62


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      10.5. OISP Remains in Path....................................64
      10.6. Return of Call to OISP..................................66
      10.7. PSTN Origination........................................67
      10.8. PSTN Termination........................................69
      10.9. Call Completion By Releasing Call Back to PSTN..........71
   11. Operator Services Example Call Flows.........................74
      11.1. Network Controlled Coin Calls...........................74
      11.2. Busy Line Verification and Interrupt....................80
         11.2.1. PSTN Target........................................81
         11.2.2. SIP Target.........................................83
      11.3. Inward Calls............................................86
      11.4. Intercept...............................................87
         11.4.1. Intercept Request Via SIP..........................87
         11.4.2. Intercept Request Via PSTN.........................90
      11.5. Operator Assisted Collect Call..........................92
      11.6. Operator Assisted Third Party Billing...................99
   12. Summary and Conclusions.....................................103
   13. Security Considerations.....................................104
   14. IANA Considerations.........................................104
   15. Acknowledgements............................................104
   16. References..................................................105
      16.1. Normative References...................................105
      16.2. Informative References.................................105
   Author's Addresses..............................................108

1. Introduction

   Information Services are services whereby information is provided in
   response to user requests. This may include involvement of a human
   or automated agent. Information Services may include call completion
   to a requested telephone number and other extensions provided on
   behalf of the owner of the information, such as assistance with
   purchases. The users normally access the Information Services by
   dialing an appropriate dialing sequence and verbally requesting an
   operator or automated system for the information. Examples of such
   dialing sequences for directory assistance currently include "411"
   or "1-NPA-555-1212" in North America, or "118xxx" in many European
   countries. Dialing sequences for operator services in North America
   often include "0" either by itself or as a prefix. In Europe the
   dialing sequence varies by country, but may include "00", or "100"
   plus additional digits depending on the service being requested. The
   users may also request information through other access methods,
   such as chat (IM), email, Web (HTTP) or SMS initiated requests. The
   Information may be delivered to the user via any mode, such as
   verbal announcements, chat (IM), email, Web (HTTP), MMS, or SMS.




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   A popular existing Information Service is Directory Assistance (DA).
   DA is a well known service in today's PSTN, and is generally
   identified with "411" or "NPA-555-1212" type services in North
   America. Today's DA services provide a user with telephone number
   associated with a name and locality provided by the user, can
   complete the call for the user, and can send SMS with the listing to
   the user's wireless phone. Other Information Services provide the
   user with a wide range of information, such as movie listings and
   the weather.

   Moving ahead, Information Services providers envision exciting
   multimedia services that support simultaneous voice and data
   interactions with full operator backup at any time during the call.
   For instance, a directions Information Service may announce and
   display directions to the requested listing, with the option for the
   caller to request transfer to an operator with the latest call
   context information.

   Operator Services are traditional PSTN services which often involve
   providing human or automated assistance to a caller, and often
   require the specialized capabilities traditionally provided by an
   operator services switch. Market and/or regulatory factors in some
   jurisdictions dictate that some subset of Operator Services continue
   to be provided going forward. Some examples of such services include
   collect calls, third party billed calls, and busy line verification.

   Operator and Information Services providers are planning to migrate
   to SIP based platforms, which will enable such advanced services,
   while continuing to support traditional DA services.

   Implementing Operator and Information Services with SIP will require
   the exchange of certain information, and possibly the use of
   specialized capabilities which are not normally required for other
   types of calls. This document aims to identify such information, and
   stimulate discussion about how this information could be exchanged.
   Existing mechanisms will be used where appropriate, and currently
   existing proposals will be favored over new extensions.

   Some of the services discussed in this document are based on
   Operator Services offered in North America. Also, many of the
   signaling issues described are based on North American PSTN
   signaling. However, the ideas in this document are not intended to
   be exclusive to North America, and are intended to be useful in
   other environments as well.

   For Operator Services, the intention is to describe how current
   operator services can continue to be provided to PSTN based


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   subscribers via a SIP based operator services architecture. It also
   looks at how current operator services might be provided to SIP
   based subscribers via such an architecture, but does not consider
   the larger question of the need for or usefulness or suitability of
   each of these services in such an environment. Specifically, many of
   the constraints and assumptions regarding access to wireline
   services via a copper loop, under which services such as Busy Line
   Verification, Interrupt, and services where the operator controls
   the "line" make sense, do not have natural parallels in a SIP based
   environment. Some of these services are treated here for
   completeness.

   A basic architecture utilizing an application server as the primary
   controller, performing third party call control to route incoming
   calls among media servers, operator workstations, etc. is described.
   Interface to the PSTN is described using PSTN gateways which
   interwork between ISUP or MF signaling and SIP.

   Operator services in the North American PSTN often utilize MF
   trunks. As there is currently no specific specification for MF/SIP
   interworking, we assume that the PSTN gateway performs an internal
   MF to ISUP translation.

   The use of existing SIP mechanisms is described where possible. Some
   of the main mechanisms described include third party call control,
   the REFER method with several extensions (e.g. Replaces), the Join
   header, Netann, and some of the ongoing work in the MEDIACTRL
   working group.

   It is assumed that appropriate business relationships are in place
   between involved providers, and that the providers involved have
   trust relationships as described in [RFC3325]. In other words, this
   document does not assume general operation on the open internet, but
   rather between sets of providers with appropriate business and trust
   relationships. Individual providers may decide to provide handling
   for other requests, but this is beyond the scope of this document.



2. Protocol Gaps

As indicated above, one of the purposes of this document is to identify
gaps in existing protocols, with respect to implementing Directory
Assistance and Operator Services in SIP. Several gaps have been
identified, and these are listed in this section of the document for
convenience to the reader. These include:



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   o  Originating Line Information/ANI II Digits

   o  Charge Number

   o  Coin Deposit Tones

   o  Carrier Information: ISUP TNS, CIP, and CSI parameters, and
      "cic", "dai" tel URI parameters



3. Terminology

   This section defines terms that will be used to discuss Information
   and Operator Services.

   "0-" ("zero minus") Dialing - Invocation of Operator Services by
   dialing "0" with no further digits.

   "0+" ("Zero Plus") Dialing - Invocation of Operator Services by
   dialing "0" followed by a phone number.

   Application Server (AS) - An Application Server is a server
   providing value added services. It controls SIP sessions on behalf
   of the services supported by the service provider's network.

   Back End Automation - Back End Automation refers to automation of
   the function that provides listing information to the caller. This
   includes playing a verbal announcement with the listing information,
   and may also include prompting the user for additional service
   requests (e.g., call completion service).

   Branding - Branding is a service where customized announcements are
   provided to the caller to identify the service provider. For
   example, if the service is provided to a Home Provider's subscribers
   by a third party provider, branded service might include a message
   thanking them for using that Home Provider. Thus the user experience
   is that the service is provided by their Home Provider rather than
   some third party. Branding can be influenced by a number of factors,
   including but not limited to the identity of the caller's Home
   Provider, or of other providers involved in the call.

   Call Completion - Call Completion is a service where a call is
   initiated by the provider on behalf of the user. For example, in the
   DA service, once the DA provider has identified the requested
   listing, it may offer to complete the call for the caller, usually



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   for some additional fee. This relieves the user from having to
   remember the number and then dial it.

   DA Provider - The DA provider is the provider of DA services to end
   users. Since DA services are a subset of IS services, a DA provider
   is also an IS provider, and the definition of IS provider holds true
   for DA provider, except that the scope of services is limited to DA
   services.

   Front End Automation - Front End Automation refers to automation of
   the initial customer contact, whereby a branded announcement may be
   played, a prompt is played to the user, and the user's spoken
   request is recorded. Speech recognition and querying for the listing
   information are performed as part of front end automation.

   Home Provider - The service provider who is responsible for
   providing voice services to the calling customer. This is the
   service provider that has the business relationship with the calling
   customer. The identity of the home provider influences call
   processing treatment, such as branding and operator queue selection.

   Home Subscriber Server (HSS) - The Home Subscriber Server is an IMS
   network element similar to a Home Location Register. It is a
   database containing information about the subscriber, user
   equipment, filter criteria for call processing triggers, etc.

   Information Services (IS) Provider - The IS provider is the provider
   of Information Services to end users. The Information Services
   provider provides retail services directly to end users, and
   provides wholesale services to other service providers.

   Intermediate Provider - In the context of this document, an
   Intermediate Provider is a provider which has agreements with home
   providers to handle OIS requests, and with OISPs which actually
   provide the requested services. Note that some home providers will
   have direct relationships with OISPs, rather than using an
   Intermediate Provider. Intermediate Providers are the targets of SIP
   requests from home providers since they are involved when a home
   provider does not have a direct relationship with an OISP.
   Intermediate Providers perform retargeting of received SIP requests
   toward the OISP. Intermediate providers make service level
   decisions, such as receiving requests for a service (such as DA
   calls) from other networks, deciding which provider will actually
   provide the service, and forwarding the request to that provider,
   retargeting the Request-URI as necessary.




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   Layer 3 connectivity - This refers to IP connectivity, for example
   as provided by an Internet Service Provider or Managed IP service
   provider. If one entity has Layer 3 connectivity to another entity,
   then it can route packets to that entity. This does not imply
   anything about any physical path between the entities. Nor does it
   imply any application layer connectivity between the entities.

   Media Server - A Media Server is a general-purpose platform for
   executing real-time media processing tasks. Examples of typical
   functions performed by media servers include playing announcements,
   collecting speech and/or DTMF digits, and performing conferencing
   functions.

   Operator and Information Services Provider (OISP) - In this
   document, this term refers to an Information Services Provider,
   Directory Assistance Provider, or Operator Services Provider,
   depending on the context. This term is used for brevity. We are also
   defining this to be an adjective, thus "OISP services" is a
   convenient, intuitive way to say "Operator and Information
   Services".

   Operator Services - Traditional PSTN services which often involve
   providing human or automated assistance to a caller, and often
   require the specialized capabilities traditionally provided by an
   operator services switch. Some examples of such services include
   collect calls, third party billed calls, and busy line verification.

   Retail OIS service - A retail OIS service is one which is provided
   to a user by the user's Home Provider.

   SIP Layer connectivity - When two SIP service providers interconnect
   for the purpose of exchanging SIP sessions or calls, they are said
   to have SIP layer connectivity to one another.

   Time Division Multiplexed (TDM) Local Exchange Carriers (LECs) -
   ATDM LEC provides local exchange service to end users utilizing TDM-
   based switching systems.

   Transit Provider - In the context of this document, a transit
   provider simply "moves calls", and has no concept of OIS services.
   It may perform SIP rerouting of the request, but does not perform
   SIP retargeting. Such a provider is used when a provider cannot
   directly route calls to another provider. For example, an
   Intermediate Provider might use a Transit Provider if for some
   reason (e.g. error condition) it cannot route a call directly to an
   OISP. This is in contrast to an Intermediate Provider (see
   definition earlier in this section).


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   Whisper - During front end automation, the OIS-MS will record and
   may time compress the caller's perhaps meandering speech into what
   is known as the "Whisper". This is intended to be played into a
   human operator's ear, should the call be referred to an operator, to
   avoid the operator from having to prompt the caller again. The
   whisper is obtained during the front end automation, and saved as an
   audio file.

   Wholesale OIS service -A Wholesale OIS Service is one which is
   provided to a user by a Service Provider other than the user's Home
   Provider.

   Zero Minus ("0-") Dialing - Invocation of Operator Services by
   dialing "0" with no further digits.

   Zero Plus ("0+") Dialing - Invocation of Operator Services by
   dialing "0" followed by a phone number.



4. High Level Requirements

   In addition to all-IP scenarios, it must be possible to support
   interworking with existing PSTN and wireless based providers, via
   both SS7 and MF interconnections.

   It must be possible to support collection of usage information. This
   includes both online and offline usage information. It must be
   possible to perform usage collection for all actions associated with
   a particular call, and further to be able to correlate actions
   across multiple provider elements and across providers.

   It must be possible to support multiple Operator and Information
   Services Providers (OISPs) per originating provider. The choice as
   to which OISP to be used could be on a per subscriber basis, or on
   other criteria.

   It must be possible to support multiple OISP providers per call. For
   example, one provider might be used for front end automation, and
   another used for operator assistance.

   It must be possible to provide an automated announcement to the
   user, and prompt the user for the type of query and query
   information.

   It must be possible to pass a "whisper" to the operator workstation.



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   It must be possible to connect the user to a human operator.

   It must be possible to provide an automated announcement of the
   requested information.

   It must be possible to prompt the user for call completion.

   It must be possible to perform call completion.

   It must be possible to support the case where OIS services are
   provided by the caller's Home Provider. This scenario is known in
   the OIS industry as the Retail scenario. In this case, the caller's
   Home Provider is also an OISP, and provides OIS service to its own
   subscribers. This is illustrated in the following figure:

   +--------+    +--------------------+
   | Caller |----| Home      +------+ |
   |        |    | Provider  | OISP | |
   |        |    |           +------+ |
   +--------+    +--------------------+

                Figure 1 Services Provider by Home Provider



   It must be possible to support the case where OIS services are
   provided by a direct third party provider. In this scenario, the
   OISP is a third party service provider, and there is direct SIP
   layer connectivity as well as business relationships between the
   calling user's provider and the OISP. This is illustrated in the
   following figure:

   +--------+    +----------+   +------+
   | Caller |----| Home     |---| OISP |
   |        |    | Provider |   |      |
   +--------+    +----------+   +------|


        Figure 2 Services Provider by a Direct Third Party Provider



   It must be possible to support the case where services are provided
   by an indirect third party provider. In this scenario, the OISP is a
   third party provider, but the caller's Home Provider does not have
   direct SIP connectivity to the OISP. Further, it's possible that it
   has no business relationship with the OISP. The caller's provider


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   routes the call to a provider with whom it does have a relationship,
   referred to in this document as an "intermediate provider", and this
   intermediate provider in turn routes either to the OISP, with which
   it has a relationship, or there could be multiple intermediate
   providers. This is illustrated in the following figure:

   +--------+    +--------+   +---------+   +------+
   | Caller |    |Home    |   | Inter-  |   | OISP |
   |        |----|Provider|---| mediate |---|      |
   |        |    |        |   | Provider|   |      |
   |        |    |  (A)   |   |   (B)   |   |  (C) |
   +--------+    +--------+   +---------+   +------+

      Figure 3 Services Provided by an Indirect Third Party Provider



   It must be possible to support the case where transit providers are
   included between any other providers involved in the call. The
   transit provider only "moves calls" between other providers, and is
   involved in no other way with OIS services. I.e., it simply forwards
   the call towards the destination, without making any service level
   decisions, in contrast to an Intermediate provider as described
   previously. This is illustrated in the following figure:

   +--------+    +--------+   +--------+   +---------+   +------+
   | Caller |    |Home    |   |Transit |   | Inter-  |   | OISP |
   |        |----|Provider|---|Provider|---| mediate |---|      |
   |        |    |        |   |        |   | Provider|   |      |
   |        |    |  (A)   |   |  (B)   |   |   (C)   |   |  (D) |
   +--------+    +--------+   +--------+   +---------+   +------+

                Figure 4 Involvement of a Transit Provider



   It must be possible to support both Information Services as well as
   Operator Services. Examples of Operator services include Operator
   Intercept, Busy Line Verification, Call Restrictions, etc.



4.1. Potential Future Requirements

   The following are potential future requirements.




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   Operation via the general internet, not specific to any particular
   SDO's architecture, and not depending on any protocol extensions
   specific to those architectures, should be supported.

   It must be possible to support non voice initiated Information
   Services requests. Possible examples include chat (IM), email, Web
   (HTTP) or SMS initiated requests. In the case that the subscriber
   makes a purchase via some online auction service, that subscriber
   can via IM or email request the assistance of an operator.

   It must be possible to provide an application interface to other
   types of systems. An example could be a web based API, so that once
   some online search engine has located some business listing, the
   services of the Information Services provider could be invoked by
   the user from the web page.

   It must be possible to support IPTV interactive services. As
   multiple services such as IM and telephony are integrated with IPTV,
   it must be possible to initiate Information Services requests in
   this context as well.



5. Information Services

   Information Services (IS) are services whereby information is
   provided in response to user requests. This may include involvement
   of a human or automated agent. Usually, the user accesses the
   Information Service by placing a voice call to the automated
   Information Service and verbally requests the information, such as
   phone number, movie listings, weather, etc. Frequently, a live
   operator is attached to recognize the user's verbal request.
   Sometimes, the user can utilize other access methods, such as SMS,
   IM, or HTTP-initiated requests. These additional methods are not
   currently covered in this document.

   Information Services are often provided on a wholesale basis to Home
   Providers, and include features such as branded announcements.

   Directory Assistance (DA) is a specific type of Information Service
   whereby end users request a telephone number for an entity.

   Purchase services and Concierge services facilitate the Information
   Services operator providing assistance to the caller after the
   listing has been announced and perhaps call completion performed.
   The call is routed to an Information Services operator who interacts
   with the customer, offering to help make a purchase. Concierge


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   service is similar; the Information Services operator offers to make
   e.g. restaurant reservations for the caller.

   The following represents a list of representative steps taken during
   the course of a typical DA request and identifies a set of required
   high level capabilities.

   1. Initial recognition of an OIS call. At some point, the call needs
   to be identified as an OIS call, and appropriate routing or other
   logic must be invoked in order to fulfill the request. This could be
   based on any number of criteria, including but not limited to
   analysis of the "address information" - e.g. the digits or Request-
   URI emitted by the caller's UA. This could occur at any number of
   places - e.g. in the caller's UA, in a proxy in the home provider,
   or in some downstream element.

   2. Identification of the requested service. There are many possible
   OIS services, and the number of these is only expected to increase
   as providers respond to customer needs. At some point during call
   processing it is necessary to identify exactly which service is
   desired. For example "directory assistance with call completion" is
   a service where after the listing information is provided to the
   caller, the option is provided for the call to be placed
   automatically, so the customer need not hang up, remember the
   digits, and dial the number. Another example is "directory
   assistance only", where call completion is not offered. There are
   multiple factors which could affect the service which is to be
   offered, and the logic deciding this could be located anywhere along
   the path to the OIS provider. Some of the information required to
   make such decisions could include:

     o   The digits dialed by the caller.

     o   The Request-URI emitted by the caller's UA.

     o   The identity of the calling party, for instance the calling
        party number.

     o   The charge number associated with the caller's account.

     o   The identity of the calling party's home provider.

     o   The identity of the provider which directly hands off the call
        to the OISP.

     o   The identity of other provider which the request might
        traverse


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     o   The Originating Station Type, in case the call was originated
        in the PSTN.

     o   Trunk group information, in case the call was originated in
        the PSTN.

     o   Capabilities and characteristics of the caller's user
        equipment.



   3. Routing of the OIS call. The call must be routed towards an
   entity which can provide the requested service. Each entity or
   network handling the call routes it based on the logic located in
   that provider, and the information currently available. For
   instance, the home provider may know very little about OIS services,
   having farmed that service out to another provider. Consequently it
   might simply route all such calls towards the OIS provider, which
   decides which service is to be offered.

   4. Authentication. When one provider passes a call to another
   provider, there is a need for the providers involved to be sure of
   each other's identity. This might be through explicit security
   mechanisms such as mutual TLS or security gateways using IPSec
   tunnel mode, it might be through reliance on a closed set of trusted
   interconnected providers, or some other policy set by the providers
   involved.

   5. Receipt of the OIS call. The OIS provider needs to be able to
   receive such calls.

   6. Querying upstream providers for information. The OISP, or an
   intermediate provider may require information from an upstream
   provider. For instance, the capabilities and characteristics of the
   caller's equipment may be needed in order to influence call
   processing.

   7. Selection of automated voice platform. When it has been
   determined that the call must be routed to an automated voice
   platform, there are a number of factors to be taken into account to
   determine an appropriate, available platform for the call. It must
   be possible to determine an appropriate, available automated voice
   platform to which the call should be routed.

   8. Connection of caller to automated voice platform. The OISP must
   be able to connect the caller to an appropriate automated voice
   platform.


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   9. Provision of branded announcements. The OISP must be capable of
   providing custom announcements to the caller based on a number of
   criteria. For example, it might greet the caller, thanking them for
   using their Home Provider's service. Though the service is actually
   provided by the OISP, business arrangements would dictate such
   branded announcements.

   10. Query the caller. The OISP must be capable of playing a voice
   request to the customer asking them for the listing. For example
   "Name and city, please."

   11. Recording a spoken request. The OISP must be capable of
   recording the caller's spoken request. This both for speech
   recognition, and also for playing back the "whisper" to a human
   operator should one be required, to prevent having to ask the
   customer to repeat the request.

   12. Speech recognition. The OISP must be able to pass the caller's
   spoken request to speech recognition system, suitable for querying a
   listing database.

   13. Listing database query. The OISP must be capable of querying one
   or more listings databases using the request.

   14. Decide to use human operator if listing query fails. If the
   listing query fails, or the speech recognition fails, the OISP must
   be able to decide to send the call to a human operator.

   15. Selection of appropriate operator. When it has been determined
   that the call must be routed to a human operator, there are a number
   of factors to be taken into account to determine the appropriate
   operator for the call. It must be possible to determine an
   available, appropriate human operator to which the call should be
   routed.

   16. Routing of call to operator workstation. Once the appropriate
   operator has been identified, the call must be routed to that
   operator's workstation.

   17. Whisper. Once the operator answers the call, the previously
   recorded request should be played to the operator as a "whisper",
   prior to connecting the caller to the operator.

   18. Connection of caller to operator. Once the operator has heard
   the whisper, the caller can be connected to the human operator. The
   operator queries the caller for the request, and initiates a query
   to the listing database.


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   19. Playing listing information. Once the listing information is
   returned from the database, the caller must be connected to a media
   resource which speaks the listing information to the caller.

   20. Prompting for call completion. If the identified service
   includes call completion, the caller should be prompted for this
   service, for example by pressing some DTMF key. In such a case, the
   AS would instruct the MS to prompt the user, and collect any DTMF
   stimulus from the user. The MS would do so, and would report back to
   the AS whether the DTMF stimulus was received.

   21. Call completion. If the caller requests call completion, the
   call should be automatically initiated for the caller.



6. Operator Services

   Operator Services are traditional PSTN services which often involve
   providing human or automated assistance to a caller, and often
   require the specialized capabilities traditionally provided by an
   operator services switch. Market and/or regulatory factors in some
   jurisdictions dictate that some subset of Operator Services continue
   to be provided going forward.

   This document assumes an architecture with SIP based OISPs, SIP
   based home providers, and SIP based end users. Since it is necessary
   to maintain backward compatibility with traditional TDM based
   providers and end users, these are also considered. It may not be
   necessary, desirable, or technically feasible to support every
   existing Operator Service using SIP, or to support both SIP and TDM
   based end users for all Operator Services. This is the subject of
   ongoing investigation, and the current iteration of this document
   assumes that both SIP and TDM based home providers and end users are
   in scope for these services, unless specifically indicated to the
   contrary. A future revision may update this assumption based on the
   findings of the investigation.

   With respect to Operator Services, this iteration of this document
   intends to provide an introduction to and descriptions of some of
   these services, as well as provide some high level requirements. It
   is intended that the subsequent iteration will build upon this,
   providing more detailed requirements, suggested SIP mechanisms, and
   more call flows.





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   Operator Services are typically provided by the requesting party's
   OISP. In some cases, such as Busy Line Verification, the target or
   called party's OISP may be involved as well.

   Next, several traditional Operator Services will be described. As
   indicated above, the current iteration of this document is silent
   regarding which of these may or may not be candidates for
   implementation with SIP, or towards SIP end users. Note that unless
   specifically indicated, most of these services are traditionally
   provided by the caller's OISP.

   Operator Assistance. This allows the caller to perform either "zero
   minus" or "zero plus" dialing to be connected to a human or
   automated system for assistance with the call.

   Collect calls. This allows the caller to request that the called
   party accept the charges for the call. Typically an OISP utilizes a
   human operator or automated system to provide this service.

   Rate Quotes. This allows the caller to request a quote for the cost
   or rate for specific calls.

   Third party billed calls. This allows the caller to request that a
   third party (different than the calling or called party) be
   contacted and requested to accept charges for the call (although in
   some limited cases, contacting the third party is not necessary).

   Busy Line Verification and Interrupt. This allows a caller to have
   the OISP determine whether a target line is in use, and if so, to
   "barge in" to the conversation and request whether the target party
   is willing to accept a call from the caller. This service is
   initially handled by the caller's OISP, which then contacts the
   target party's OISP, which is able to perform the verification and
   interrupt on the target party.

   Coin Calls. Operator services systems must be able to control TDM-
   based network controlled coin stations (payphones). This includes
   monitoring of coin deposit tones (to verify payment) sent from the
   coin station, as well as sending supervision (control) signals to
   the coin station. Network controlled coin stations are connected to
   TDM based end offices via specialized phone lines which support the
   required signaling. These end offices, in turn, connect to TDM based
   OISPs using specialized trunks capable of conveying the coin
   signaling. The OISP monitors and controls the coin station via these
   trunks. "Smart" coin stations perform coin detection locally and do
   not require network control, and are not discussed here. This
   service is provided by the OISP associated with the coin station.


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   Emergency Calls. Sometimes a caller dials "0" instead of the
   standard emergency dialstring, resulting in placement of an
   emergency call to the OISP. The OISP must properly route such a call
   toward the PSAP. This service is provided by the caller's OISP.

   Calling Card Billing Service. This enables a calling party to bill a
   call to a calling card number.

   Commercial Credit Card Billing Service. This enables a calling party
   to bill a call to a commercial credit card.

   Directory Assistance (DA). In some contexts, DA is considered as an
   Operator Service. Within the context of this document, we consider
   DA as an Information Service, which is related to but distinct from
   Operator Services.

   The following sections describe an initial set of basic high level
   capabilities required for supporting Operator Services. The
   capabilities for Information Services generally apply for Operator
   Services as well. This work is currently under study, and a complete
   set of required capabilities is expected to be identified in the
   near future. Similarly to the required capabilities for Information
   Services, the use of existing SIP mechanisms will be investigated
   for providing these capabilities.



6.1. Inter Provider Capabilities

   Ability to accept requests from other providers. This is the ability
   to accept incoming OIS requests from other providers, including home
   providers, intermediate providers, and transit providers.

   Ability to terminate calls to other providers. This applies to call
   completion services, as well as other services such as third party
   billing.



6.2. Inter OISP Capabilities

   These are capabilities between OISPs.

   Inward connection. This is a call from one OISP to another, e.g. so
   that the originating OISP may request services from the terminating
   OISP. One example of this is Busy Line Verification, where the
   caller calls their own OISP, and this OISP places an "inward" call


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   to the target party's OISP, which would have the capability to
   perform the verification of the target party.

   Transfer between OISPs. In this case, one OISP transfers the call to
   another OISP, to be handled by that OISP, so that the first OISP is
   no longer in the signaling path.

   Moving connection from one OISP to another. An example of this case
   is where one OISP farms out a specific service to another OISP. The
   first OISP performs initial handling of the call, to determine the
   desired service. The call is sent to a different OISP with which the
   first has a relationship. The first OISP remains in the signaling
   path, and when the provided service is complete, the first OISP
   determines what if any additional processing may be necessary. This
   is similar to a third party call control type arrangement.



6.3. Intra OISP Capabilities

   Note that some of the following capabilities may be required for
   inter OISP scenarios as well; this is the subject of ongoing
   analysis and is not covered in the current iteration of this
   document.

   Placing a caller on hold, possibly with announcements. This is used
   in many services, including Information Services.

   Exchanging information between Application Server and Operator
   Workstations/Automated Platforms. This capability is required
   whenever an operator workstation or automated platform is used.
   Because an Operator Workstation interacts with a human user, it is
   expected that additional information, beyond that which an automated
   system would exchange with an application server, will be required.
   Further, several modes of application server control are currently
   under investigation. The first is where the workstation or automated
   platform is more or less autonomous, and is capable of initiating
   calls and directly impacting call processing. The other is more of a
   master-slave relationship, where the AS is in complete control. The
   master-slave model requires that more information be exchanged with
   the AS than does the autonomous model. Other models may be possible.

   Queuing and call distribution. Resources including human operators
   and automated platforms need to be tracked and managed, and the
   appropriate resource of the appropriate type needs to be selected on
   a per invocation basis. What is needed is that for a particular
   call, that a set of criteria be provided and the best match resource


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   be selected. This is the job of the ACD server. Some means is needed
   to communicate the selection criteria for human operators and
   automated platforms to the ACD server.

   Operator Registration and Location. Human operators may not be
   interchangeable, and have specific attributes such as skillsets
   which can be used to identify the best human operator to service a
   particular call. Operators log in at workstations at the beginning
   of a shift, and log out during breaks and at the end of a shift. It
   is important to associate each available operator with the
   workstation at which they are logged in, so that requests can be
   sent to the appropriate human operator. This is needed because the
   selection process described above identifies a particular human
   operator; it is then necessary to identify the workstation at which
   that operator can be reached.

   Bridging and removal of operator or automated system. Many operator
   services require that either a human operator or automated system be
   "bridged" onto a call, and to be removed at some point.



6.4. Capabilities Required for Specific Services

   Connection Hold and Ringback. This capability involves having the
   OISP "hold" the connection, such that the originating caller remains
   connected, even if they attempt to hang up. This is mainly used in
   relation to emergency services. Ringback is the ability for the OISP
   to call back the calling party after they have hung up. This too is
   often used in conjunction with emergency calls. Note that these are
   only discussed in this document in the context of controlling a PSTN
   based endpoint, as this capability does not carry over directly to
   SIP based endpoints.

   Coin Station Control. This is the ability of the OISP to determine
   the coinage deposited into a TDM based network controlled coin
   station (as opposed to an "intelligent" coin station which performs
   such functions locally). This involves interpretation of the coin
   control signals sent via specialized trunks from the end office to
   which the TDM based coin station is connected via a specialized
   phone line. Additionally, the need to signal toward the coin station
   needs to be supported as well, for example to instruct the station
   to return coins to the caller. This capability is intended to
   interact with the specialized coin trunk.

   Network Service Recall. After a call resulting from Operator
   Services is completed, the caller may signal the desire to return


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   back to the OISP, without placing another call. In the traditional
   PSTN, this is typically accomplished by the user signaling a hook
   flash or other distinctive stimulus.

   Verification and Interrupt. This is used in the Busy Line
   Verification and Interrupt service, and allows the OISP to determine
   if the target number is in use, to listen to a scrambled
   representation of the conversation, and to interrupt the target
   party's conversation to ask if they would accept a call from the
   caller.

   Transfer of emergency services call to selective router. Sometimes a
   caller places an emergency call using a dial string which invokes
   operator assistance (such as "0" in North America), rather than an
   emergency call dial string. In such cases, the OISP must be able to
   pass the emergency call to the appropriate PSAP. Handling of these
   types of calls is outside the scope of this document. Standards for
   emergency calling with SIP are still in development.



7. OISP Internal Architecture

   This section describes an initial view of the elements internal to
   the OISP architecture.

   The following types of elements may be present within the OISP
   infrastructure:

   Automatic Call Distributor (ACD) server - The ACD provides queuing
   and call distribution functions for human operators. Specifically,
   it is the component that tracks the availability of the human
   operators and selects an available operator utilizing complex
   algorithms based on operator skills, type of call, type of request,
   calling party information, etc. Similar functionality is required
   with respect to automated platforms. The ACD server is modeled as an
   Application Server. Two different models of ACD include a "query"
   model, where the ACD accepts a request and returns a response (such
   as a SIP redirection response) identifying the selected resource,
   and an "inline" model, where the ACD server accepts a request and
   inserts itself into the signaling path, making its selection and
   sending requests to that resource. There is currently work in the
   MEDIACTL working group regarding Media Resource Brokers (MRBs) which
   may be relevant to this.





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   The ACD server may also contain functionality for tracking and
   maintaining statistics about resource utilization; this is sometimes
   referred to as force management.

   Customer Profile Database - The Customer Profile Database is a per
   subscriber database maintained by an OISP about its customers. Some
   of this information might be statically provisioned, other
   information such as customer preferences or session information
   might be populated dynamically as a result of customer interactions.

   Messaging Gateways - Messaging Gateways provide access and data via
   E-mail, SMS, MMS, WAP.

   Operator and Information Services Application Server (OIS-AS) - The
   OIS-AS contains AS functions specifically for directory assistance
   and information services as well as other Operator Services. This
   may coordinate multiple call legs, connecting the caller in sequence
   to one or more OIS-MS and/or operator workstations according to the
   logic contained within. The OIS-AS may need to communicate with
   elements of other providers, for instance to query information about
   the capabilities and characteristics of the caller's equipment, or
   to access another provider's operator resources.

   Operator and Information Services Media Server (OIS-MS) - The OIS-MS
   provides the media resources for playing announcements, performing
   voice recognition, performing listing database queries, generating
   whisper from the user's verbal request, etc.

   Operator Workstations - Operator Workstations provide an interface
   to the human operator. They may receive the customer's recorded
   request (e.g. name and city of requested listing), information from
   listing or other databases, and also terminate a multimedia session
   with the customer. Operator workstations are specialized SIP
   endpoints, and may be modeled in various ways, such as UAs or media
   servers.

   PSTN Gateways - OISPs need to interface with the PSTN. Thus,
   gateways are needed to interface between the OISP and both signaling
   and bearer. The bearer is handled by trunk gateways, which interface
   RTP streams on the OISP side to TDM trunks on the PSTN side. The
   signaling may be handled by signaling gateways which interface SS7
   on the PSTN side and SIP on the OISP side. Currently in North
   America, inband signaling on MF trunks is common for interfacing to
   OISPs, and trunk gateways need to be able to interpret and report as
   well as generate the appropriate MF signaling.




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   Service Databases - Service Databases store service specific
   information (e.g. listing information such as name, address, and
   phone number, etc.) These may be located in the OISP's network
   and/or in other networks, and more than one may be used.

   SIP Proxy - One or more SIP proxies may be present in the OISP
   network, to facilitate SIP communications with other providers as
   well as to perform call processing functions between OISP
   components.

   The following figure shows a simplified view of an OISP internal
   architecture. The lines show logical connectivity; elements
   communicate via the proxy. A single OIS-AS is shown, along with up
   to "k" OIS-MS and up to "m" Operator Work Stations, and an ACD
   server. Communications between elements are assumed to traverse a
   proxy, which has been omitted from the figure for brevity.


                +--------+   +---------+   +---------+
                | OIS-AS |-+-| OIS-MS1 |...| OIS-MSk |
                +--+-----+ | +---------+   +---------+
                   |
                   |       | +---------+   +---------+
                   |       +-| OWS1    |...| OWSk    |
                +--+--+    | +---------+   +---------+
                | ACD |    |
                +-----+    | +--+---+
                           +-|PSTNGW|
                             +------+

          Figure 5 Simplified view of OISP Internal Architecture



8. General Approach

   This section describes one possible way to implement DA using SIP.
   Other ways may be possible.

   The general approach involves having the OIS-AS host most of the
   processing logic, and to control the call in general. The OIS-AS
   implements a third party call control (3PCC) functionality, as
   described in [RFC3725]. It terminates the signaling dialog from the
   caller, and originates dialogs towards other components as
   necessary. There may be multiple sequential sessions set up during
   the course of a DA call.



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   For example, the OIS-AS would initiate a new dialog towards a MS for
   front-end automation. When it gets the 200 OK from the MS with SDP,
   it passes that SDP back toward the caller. When the front end
   automation has completed, the OIS-MS sends a BYE containing message
   bodies conveying the success of the operation (i.e., was it able to
   obtain the listing) as well as any data related to the operation. In
   case of success, the body might carry the listing information, or a
   URI pointing to it. In case of failure, it might carry a URI
   pointing to the whisper file.

   In case of failure, the OIS-AS would determine that the call needs
   to be routed to a human operator. The OIS-AS first needs to identify
   a suitable operator to handle this request. The ACD server has this
   responsibility, and could be implemented as a redirect server facing
   the OIS-AS, redirecting towards the best suited available operator.
   Facing the operator workstations, the ACD server could be
   implemented as a presence server, maintaining availability of each
   operator, as well as the associated information for each (e.g.
   languages, skill level, cost, etc).

   The OIS-AS would then send an INVITE toward the identified operator
   workstation. This INVITE includes the caller's SDP as well as a URI
   pointing to the whisper file. The workstation could play the whisper
   to the operator as the call is answered. The operator workstation's
   SDP would be passed back to the caller via a re-INVITE or UPDATE
   request.

   If the operator is successful in locating the desired listing, the
   workstation would send a BYE containing message bodies with an
   indication of success, and either the listing information of a
   pointer to the same.

   The OIS-AS would then initiate a call leg towards an OIS-MS for back
   end automation. The INVITE would include the same body with the
   listing information that was sent by the operator workstation. The
   OIS-MS returns its SDP, which the OIS-AS would propagate back over
   the originating leg via a re-INVITE or UPDATE request. The back end
   automation process includes audibly playing out the listing
   information, and possibly offering call completion service. The OIS-
   MS sends a BYE with a message body indicating whether call
   completion is desired.

   If call completion is desired, the OIS-AS sends a REFER back over
   the originating call leg to the caller, and clears the call.

   These examples describe simple voice scenarios. Other media types
   may be possible. For example, it may be desirable to send the


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   listing information via text message to the caller's terminal, or to
   show a video clip. Such features require knowledge of the calling
   terminal's capabilities and characteristics. The mechanism described
   in [RFC3840] Indicating User Agent Capabilities in the Session
   Initiation Protocol (SIP) can be used for this. The capabilities
   might have been signaled in the initial INVITE request. Otherwise,
   the OIS-AS can query for capabilities using an OPTIONS request.
   Additionally, some non SIP mechanism might be used, such as querying
   a database (e.g. IMS HSS) in the caller's network.

   References to a whisper file can be passed using the mechanism
   described in [RFC4483].

   Other information signaled via message bodies includes the success
   or failure status of operations (such as identifying the requested
   listing), or other data (such as the listing information).

   Context information may be maintained on a per call basis. It could
   include such information as the caller's preferred language, etc. A
   URI pointing to the context information could be passed between
   elements in the OISP infrastructure.

   Note that the IETF MEDIACTRL working group is currently developing
   mechanisms for control of SIP based MSs by ASs; this work may be
   applicable for OIS as well.



9. Signaling Mechanisms

   This section discusses the signaling mechanisms required to provide
   OIS services.

9.1. PSTN Protocol Interworking

   Operator Services will need to interoperate with the existing PSTN.
   This includes both receiving incoming call requests from the PSTN as
   well as initiating calls towards the PSTN. There are several issues
   which are specific to PSTN interworking.

   Current Operator Services systems use both SS7 ISUP and MF
   signaling. PSTN gateways interwork between the PSTN signaling and
   SIP signaling, and between the PSTN's circuit switched bearer
   channels and RTP. [RFC3398] defines ISUP-SIP interworking
   procedures. . ATIS, which is responsible for defining North American
   specific telecommunications standards, provides North American
   procedures in [T1679]. There is currently no standard for MF-SIP


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   interworking. Since ISUP descended from MF, it's reasonable to
   assume a gateway model whereby MF signaling is logically mapped to
   ISUP, then ISUP-SIP interworking procedures are applied.

   ISUP interworking involves two mechanisms; parameter mapping and
   encapsulation. Some concepts exist natively in both PSTN and SIP
   signaling, and thus both PSTN signaling and SIP define protocol
   mechanisms for conveying such information. Mapping between these is
   specified in interworking standards such as [RFC3398] and [T1679].
   Other ISUP parameters have no direct equivalent in SIP, but are
   needed in SIP headers so that proxies and other SIP entities can
   route calls; extensions have defined SIP headers and parameters for
   this purpose. In order to convey those parameters which have no
   mapping to SIP headers, encapsulation of ISUP messages is used,
   whereby the ISUP message content is encoded in a MIME body which is
   carried in SIP messages. [T1679] specifies that the entire ISUP
   message be encapsulated in a MIME body of type "application/ISUP",
   as registered with IANA and defined in [RFC3204]. [NSS] defines a
   MIME type "application/NSS"; this standard specifies that the only
   parameters which do not have mappings to SIP be included in the NSS
   body, along with identification of the ISUP version and ISUP message
   type, rather than encapsulating the entire ISUP message. [T1679] is
   the ATIS standard for North American networks.

   Thus, PSTN gateways send SIP messages containing SIP headers and
   parameters mapped from ISUP parameters where specified, and carrying
   an "application/ISUP" MIME body containing an entire encapsulated
   ISUP messages.



9.2. Conveying Application Specific Information

   Some information carried by PSTN signaling, such as the ISUP Called
   Party Number is required for routing calls. Other information, such
   as Charge Number, is for use by applications such as operator
   services, and is not needed for routing the call.

   With SIP, information needed for routing requests, or which
   otherwise needs to be available to proxies, should be present in
   message headers. Note that proxies may add headers and modify header
   content.

   Message bodies can be carried in SIP requests and responses. Such
   bodies are generated by and consumed by endpoints, and are expected
   to be passed transparently by proxies. Additional headers such as
   Content-type and Content-disposition describe the MIME type of the


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   message body as well as how the receiving endpoint is to handle
   unsupported MIME types. Messages can contain more than one body, as
   described in [RFC2045].

   Moreover, much of the information delivered to an operator services
   system is expected to be provided by trusted equipment in the
   caller's home provider, rather than by the caller's user equipment.

   Architectures such as IMS include application servers which have the
   ability to act as Back to Back User Agents (B2BUAs). Whereas proxies
   cannot insert message bodies, B2BUAs can in fact do so, because they
   act as SIP endpoints.

   Not all information passed in PSTN signaling can be conveyed
   natively in SIP, but operator services systems expect this
   information. One option for doing this is to have an application
   server in the caller's home provider, acting as a B2BUA, populate a
   MIME body in the INVITE sent to the operator services provider, for
   consumption by an OIS AS. There is at the time of this writing no
   agreement on a MIME type to use for this purpose.

   Some ISUP information for which SIP mappings are not currently
   defined is also expected to be relevant for calls initiated using
   SIP. Charge Number is business related information, and is expected
   to apply regardless of whether a caller is using a SIP or PSTN
   device. The same is true for Originating Line Information. Again,
   the use of a MIME body is potential option. Mechanisms for some of
   this information in SIP header fields and parameters are described
   in several Internet-Drafts at the time of this writing, and are
   described in this document where applicable.

9.3. Calling Party's Identity

   In many cases, downstream providers may need to know the calling
   party's identity. This might be needed to influence call processing,
   or for usage collection purposes. Also, the calling party's identity
   in the form of a SIP URI might be needed so that the identity of the
   home provider can be determined.

   The calling party's equipment populates the From header in SIP
   messages. This is not trusted. There are several methods for
   providing "network-asserted identities", which under the appropriate
   conditions can be trusted.

   The SIP Identity mechanism defined in [RFC4474] provides a
   standardized, architecture agnostic SIP mechanism for
   cryptographically assuring the user's identity.


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   The P-Asserted-Identity header [RFC3325] is a private extension to
   SIP that enables a network of trusted SIP servers to assert the
   identity of authenticated users.

   Note that some networks may allow their users to hide their
   identity. In the current North American PSTN, for such cases the
   caller id information is often transported through the network,
   marked with a privacy indication such that it will not be presented
   to the called party. In SIP, the Privacy header field defined in
   [RFC3323] is used.

   Bilateral agreements between VOIP providers determine whether
   providers are within the same "trust domain" as defined in
   [RFC3324], and what information, including network-asserted
   identities, may be exchanged between providers. Depending on such
   agreements, it is possible that the caller identity information is
   obscured or completely absent. As indicated in [RFC3325], "Masking
   identity information at the originating user agent will prevent
   certain services, e.g., call trace, from working in the Public
   Switched Telephone Network (PSTN) or being performed at
   intermediaries not privy to the authenticated identity of the user."

   When an OIS provider is not privy based on bilateral agreement to
   network asserted identity information from the calling network when
   the caller has requested privacy, it may be unable to implement any
   call processing logic based on such information.

   If the OISP desires to reject anonymous calls, [RFC5079] defines a
   new SIP response code 433 (Anonymity Disallowed) for this purpose.

   The following shows an example of an INVITE message contain a P-
   Asserted-Identity header.

















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   INVITE sip:da@provider-c.example SIP/2.0
   Via: SIP/2.0/UDP proxy-b.provider-b.example.com:5060
   ;branch=y9hG4bK74bf9
   Via: SIP/2.0/UDP proxy-a.provider-a.example.com:5060
   ;branch=x9hG4bK74bf9
   Via: SIP/2.0/UDP client.provider-a.example.com:5060
   ;branch=z9hG4bK74bf9
   From: <sip:7327581234@provider-a.example.com>;tag=1234567
   To: 411 <tel:+411>
   Contact: <sip:7327581234@provider-a.example.com>
   P-Asserted-Identity: "732758123" <sip:73237581234@provider-
   a.example.com>
   Content-Type: application/sdp
   Content-Length: ...
   [SDP not shown]




9.4. Provider Identification

   As discussed, in some deployment scenarios, the OISP makes use of
   the identities of other providers involved in the call. This section
   discusses how those identities can be conveyed using SIP.



9.4.1. Home Provider

   In many cases, the OISP needs to identify the caller's Home
   Provider. This may be needed for branding purposes as well as to
   potentially influence treatment in other ways.

   The basic mechanism for determining the home provider is to derive
   it from the right hand side (RHS) of the network asserted identity.

   In SIP, identities are expressed as URIs. These can be SIP (or SIPS)
   URIs, or "tel" URIs.

   [RFC3261] defines the SIP URI, which is used for identifying SIP
   resources. The RHS can be expressed as a DNS domain name or as an
   IPv4 or IPv6 address. The hostname format is most suitable for
   providing an identity to reach the calling party. For instance the
   mechanisms defined in [RFC3263] for locating SIP servers depends on
   the use of domain names for the various types of DNS lookups such as
   NAPTR, SRV, and A.



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   If a provider decides to provide network asserted identities
   expressed as SIP URIs using IP addresses instead of hostnames, it
   forfeits the use of such standardized mechanisms for reaching its
   users. It also becomes difficult to derive the home provider
   identity from the network asserted identity.

   [RFC3966] defines the "tel" URI, which is used for describing
   resources identified by phone numbers. The "tel" URI format does not
   include a domain. Thus, if the network asserted identity includes
   only a "tel" URI, no direct information about the home provider is
   provided.

   The SIP Identity mechanism is intended for use with SIP URIs. The
   PAI mechanism can use either a SIP URI, a "tel" URI, or both.

   This document depends on the home provider providing a network
   asserted identity containing a hostname. This includes the SIP
   identity where the SIP URI contains a hostname, or a PAI header
   containing at least a SIP URI with a hostname.

   Very simply, the RHS of the hostname in the SIP URI is extracted and
   used as the basis to influence call processing. In cases where the
   caller's identity is not available, as discussed in the "Calling
   Party's Identity" section, then the home provider's identity is
   consequently also not available, and call processing logic based on
   such information (such as branding) cannot take place.



9.4.2. Intermediate Provider

   In some cases, the OISP may need to know the identity of an
   intermediate provider which the call has traversed. Recall that for
   our purposes, we define "intermediate provider" as having a business
   relationship with both the home provider (to handle OIS requests)
   and with an OISP (which will actually provide the requested
   service.) This may be needed to influence treatment.

   The use of the SIP History-Info mechanism defined in [RFC4244], can
   be used for this. As the call moves from one provider to the next
   and is retargeted, corresponding entries are added to the SIP
   History-Info header. If the domain name format is used for the
   retargeted entities, then the History-Info header now includes a
   list of traversed SIP domains or providers, which can be consulted
   by the OISP.




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   According to [RFC4244], entries should be added to the History-Info
   header whenever the Request-URI is modified. Cases may exist where
   the call is sent to another provider but the URI is not modified. In
   such cases, the provider is not captured by the History-Info header.

   The following figure illustrates the use of the History-Info header
   for this purpose.



    Caller        Provider-A     Provider-B     Provider-C
      |              |              |              |
      |              |              |              |
      |              |              |              |
      |(1) INVITE tel:+411          |              |
      |------------->|              |              |
      |              |              |              |
      |              |              |              |
      |              |(2) INVITE sip:da@prov-b.example.com
      |              |------------->|              |
      |              |              |              |
      |              |              |              |
      |              |              |(3) INVITE sip:da@prov-
   c.example.com
      |              |              |------------->|
      |              |              |              |
      |              |              |              |

    Figure 6 Use of History-Info header to identity traversed providers




   1. The user dials "411", and the resulting INVITE to its home proxy
   is for "tel: +411". No History-Info header is included yet.

      INVITE tel:+411 SIP/2.0
      (other message content omitted)


   2. The home proxy retargets this to "sip:da@prov-b.example.com", and
   adds a History-Info header which includes the targeted-from URI:

      INVITE sip:DA@prov-b.example.com SIP/2.0
      History-Info: <tel: +411>; index=1
      (other message content omitted)



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   3. Proxy-B retargets this to "SIP: da@prov-c.example.com", and
   appends another entry to the History-Info header:

      INVITE sip:DA@prov-c.example.com SIP/2.0
      History-Info: <tel: +411>; index=1, <sip:da@prov-b.example.com>;
      index=2
      (other message content omitted)


   When this request arrives a Proxy-C in Provider C (OISP), it conveys
   the following:

     o  The Request-URI (SIP: da@prov-c.example.com) indicates this as
        a DA call

     o  The History-Info header conveys the history of the request:

     o  It started as a tel URI for digits "411"

     o  It was then targeted to provider B

     o  It is now targeted to provider C

   Please note that if a transit provider were encountered, the transit
   provider would simply route the request toward Provider C, and would
   not perform retargeting. It would not modify the Request-URI nor the
   SIP History-Info header contents.



9.5. Originating Line Information/ANI II Value

   In the current PSTN in North America, OIS providers have the ability
   to tailor treatment based on the type of originating station. For
   instance, calls from prison phones are restricted from accessing DA
   services. Example values include POTS, coin, hospital,
   prison/inmate, cellular, etc. In the PSTN in North America, this
   information is signaled for SS7 calls using the Originating Line
   Information (OLI) information element, and in MF calls using the ANI
   II digits. To support interworking with the PSTN, it must be
   possible to convey the Originating Station Type value. The ability
   to convey this information natively with SIP is currently lacking.

   It is also desirable to characterize certain types of originating
   SIP based callers using these same values, e.g. prison, police, etc.




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   There is currently no standardized mechanism for conveying OLI
   information in SIP. Current potential options include the "cpc" tel
   URI parameter, the "isup-oli" parameter, and use of a MIME body.

   [draft-mahy-iptel-cpc] proposes a "cpc" tel URI parameter, which is
   intended to interwork the ISUP Calling Party's Category (CPC)
   parameter. It is also intended to carry information from the ISUP
   OLI parameter or from MF ANI II digits.

   For interworking with the North American PSTN, there are at least
   two issues with using this parameter to convey OLI information.

   The ANSI ISUP used in the North American PSTN makes use of the CPC
   parameter. To meet the needs of this environment, it was necessary
   to define an additional, North American specific parameter, the OLI.
   The CPC and OLI are separate parameters, which allows both pieces of
   information to be signaled separately. Since the "cpc" tel URI
   parameter can be used to convey only CPC values or OLI values, it
   does not meet the need to signal this information separately.

   Additionally, the cpc tel URI parameter is intended to convey only a
   limited subset of OLI values, and any additional desired values
   require IANA registration. However, in the North American PSTN, the
   set of OLI values is not constrained in this way. Rather, OLI
   carries a 2 digit value, and excepting a few reserved values, any of
   these could potentially be encountered.

   The "isup-oli" parameter is not standardized, but is used to carry
   the OLI information.

   For PSTN interworking, [T1679] does not specify a SIP mapping for
   the OLI parameter. Thus, it is carried in an encapsulated ISUP
   message in a MIME body. The proposed "cpc" tel URI parameter as
   currently defined is not intended to carry the entire possible range
   of ANI II values.

   For SIP originated calls, there is no currently standardized way to
   carry this information. The isup-oli parameter would be useful to
   this end.



9.6. Trunk Group Identifier

   The incoming trunk group number provides information which could be
   used to influence call processing, thus this information is needed.
   Trunks are point to point circuits and as such, their remote


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   termination point is unambiguously known. As such, knowledge of the
   incoming trunk group conveys the identity of the provider offering
   the call.

   For PSTN interworking, the incoming trunk group identifier is a key
   piece of information and must be known. Thus, at a PSTN to IP
   interworking point, the trunk group information must be kept and
   signaled forward. This holds for OISP's accepting incoming calls
   from the PSTN as well as upstream providers accepting calls from the
   PSTN.

   [RFC4904], "Representing trunk groups in tel/sip Uniform Resource
   Identifiers (URIs)" defines a way to signal incoming and/or outgoing
   trunk group information as a parameter in SIP URIs and tel URIs.

   To represent incoming trunk groups, the trunk group parameter is
   included in the Contact header of the SIP message. The "trunk-
   context" parameter should also be included, to ensure that the trunk
   group is unambiguously identified, since trunk group numbers are not
   globally unique.

   At the time of this writing, [T1679], which specifies PSTN
   interworking for North American networks, does not include this
   mechanism, possibly because it predates [RFC4904]. However, gateways
   should include this information for operator services.

   The following example shows an INVITE containing a trunk group
   identification in the Contact header:

     INVITE sip:da@provider-c.example.com SIP/2.0
     Via: SIP/2.0/UDP proxy-b.provider-b.example.com:5060
     ;branch=y9hG4bK74bf9
     Via: SIP/2.0/UDP proxy-a.provider-a.example.com:5060
     ;branch=x9hG4bK74bf9
     Via: SIP/2.0/UDP client.provider-a.example.com:5060
     ;branch=z9hG4bK74bf9
     From: <sip:7327581234@provider-a.example.com>;tag=1234567
     To: 411 <tel:+411>
     Contact: < sip:7327581234@provider-b.example.com;tgrp=101; trunk-
     context=provider-b.example.com@proxy-b.provider-
     b.example.com;user=phone>
     P-Asserted-Identity: "7327581234" <sip:73237581234@provider-
     a.example.com>
     Content-Type: application/sdp
     Content-Length: ...




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9.7. Identification of PSTN Originated Calls

   Since calls arriving via PSTN trunks may require different
   processing from those received from SIP endpoints, it must be able
   to distinguish between these types of calls. For PSTN originated
   calls, the Contact header identifies the gateway, and also the
   presence of the "tgrp" parameter in that header indicates that the
   call was received via a PSTN trunk. Obviously the presence of an
   encapsulated ISUP message also identifies the call as such.

   In some cases, the identity of the home PSTN provider of the caller
   may be known (e.g., the call arrived via a dedicated trunk group
   from a PSTN end office). In such cases, the gateway may populate the
   host portion of the SIP URI in a P-Asserted-Identity header field
   with a value of local significance within the OISP identifying that
   PSTN home provider. Conveyance of such information beyond the OISP
   is outside the scope of this document.



9.8. Dialed Digits

   Currently in the North American PSTN, the OIS provider may take into
   account the digits dialed by the user. In that scenario the dialed
   digits are frequently forwarded to the OIS provider.

   Using SIP, the dialed digits would typically be sent by the user's
   equipment in the form of a tel URI or SIP URI in the Request-URI of
   a SIP INVITE. It is possible that retargeting could take place, in
   which case the dialed digits would be lost.

   The SIP History-Info mechanism defined in [RFC4244] provides a
   mechanism for solving exactly this type of problem. It defines a new
   optional SIP header, History-Info, to provide a standard mechanism
   for capturing the request history information. Whenever a node which
   supports this mechanism modifies the Request-URI of a request, it
   captures this in the History-Info header.

   The following example shows an INVITE containing a History-Info
   header, which conveys the original dialed digits, after having been
   retargeted.

      INVITE sip:DA@prov-b.example.com SIP/2.0
      (other message content omitted)
      History-Info: <tel: +411>; index=1, <sip:da@prov-b.example.com>;
      index=2



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   Please see the section titled "Arbitrary Involved Provider" for an
   example of a flow where the History-Info mechanism delivers the
   dialed digits to the OISP when retargeting has occurred.



9.9. Retargeting to Identify the Desired Service

   It is necessary to identify the service being requested. Such
   services might include directory assistance with or without call
   completion. The logic to determine this might reside in one or more
   points in the network. Additionally, the identification of the
   service might be refined as the request traverses potentially
   multiple networks, depending on the availability of additional
   information.

   It is proposed here to retarget the Request-URI of the SIP request
   to specify the desired service. While the initial Request-URI might
   specify "SIP:411@provider-a.example.com", a downstream element might
   invoke service logic and determine that this call should be sent to
   OISP C's network for directory assistance with call completion, and
   change the Request-URI to "SIP:da-with-call-completion@oisp-
   c.example.com".

   A similar approach is taken for identifying resources in [RFC4240].

   [CSI], a work in progress, discusses explicit service identifiers
   for using in IMS [IMS] based networks.



9.10. Charge Number

   In the current PSTN in North America, a Charge Number is signaled
   with call originations. The Charge Number identifies the customer or
   account with which the caller is associated. In many cases it is the
   same as the Calling Party Number, while in others it is different -
   e.g. the main number for a business which has many individual
   calling numbers. This might be needed for usage collection, but it
   also could influence call processing, especially when a particular
   type of service applies for any caller associated with a particular
   charge number.

   There is currently no IETF standardized mechanism to convey the
   Charge Number in SIP. The need to convey equivalent information for
   SIP based callers is also under investigation.



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   [PCI] proposes a "P-Charge-Info" SIP header for carrying charge
   information for a call. It is intended to facilitate carrying
   information equivalent to OLI for SIP originated calls. It is also
   intended to support PSTN interworking by carrying the ISUP Charge
   Number value.

   For PSTN interworking, [T1679] does not specify a SIP mapping for
   the Charge Number parameter. Thus, it is carried in an encapsulated
   ISUP message in a MIME body. The P-Charge-Info header, if
   standardized, would be useful in this role.

   For SIP originated calls, there is no currently standardized way to
   carry this information. The P-Charge-Info header, if standardized,
   would be useful in this role. The use of a MIME body populated by an
   application server in the home provider's network is another option.



9.11. Access Prefix

   In the current PSTN in North America, operator services calls are
   often originated by dialing a prefix such as "0". In ISUP signaling,
   the "0" is not carried in the Called Party Number parameter. Rather,
   it is stripped, and the ISUP Operator Services Information (OSI)
   parameter carries an indication of the original access prefix.

   For SIP originations, there are several options. First, the dialed
   digits, including any prefix, can be included in the Request-URI.
   Alternatively, an AS in the caller's home provider can retarget the
   request based on the digits, such that new Request-URI identifies
   the requested service. The original dialed digits can be carried in
   the retargeted-from Request-URI in a History-Info header. For
   example, a Request-URI containing a zero plus 10 digits might be
   retargeted at an AS to sip:operator-assistance@provider-
   b.example.com. Though not currently standardized, these options can
   also be used for PSTN interworking. I.e., the GW could choose to
   prepend a prefix to the digits in the Request-URI based on the
   received Operator Services Information parameter. Additionally, the
   GW could support building a Request-URI which specifies the
   requested service, based on analysis of the incoming ISUP signaling.

   For PSTN originations, the Request-URI can be formed as described
   above for SIP originations. Additionally, this information is also
   conveyed via the Operator Services Information parameter in the
   encapsulated ISUP.




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9.12. Signaling of Carrier Information

   In North America, the handling of PSTN calls utilizing Interexchange
   Carrier (IXC) networks are subject to specific regulatory
   requirements, resulting in specific signaling requirements which may
   differ from those in other regions. Reflecting this is the
   definition of ANSI ISUP parameters not defined in the ITU-T as well
   as specific usage for certain ISUP parameters. Interworking between
   ISUP and SIP signaling for such scenarios is documented in several
   specifications, but there are issues with these specifications. This
   section identifies the ISUP parameters involved in IXC signaling in
   North America, and provides an overview of some of the issues with
   current interworking specifications. Subsequent sections will
   specifically address each parameter. The relevant ANSI ISUP
   parameters include the Transit Network Selection (TNS) parameter,
   the Carrier Identification Parameter (CIP), and the Carrier
   Selection Information (CSI) parameter.

   The ISUP Transit Network Selection (TNS) parameter is used to route
   calls to a specific carrier. In North American networks, it is used
   on several different interfaces to request that a call be routed to
   a particular carrier. TNS is also used in ITU-T ISUP.

   Specialized switches called Access Tandems (ATs) provide IXC
   networks with access to Local Exchange Carrier (LEC) switches. When
   a LEC switch originates an IXC call through an AT, it uses the TNS
   to inform the AT of the IXC to which the call is to be routed.

   Based on business arrangements, IXCs may also provide access to
   other IXCs. Thus a LEC switch may need to route a call using IXC B,
   but might have connectivity to only IXC A. The LEC switch could,
   depending on arrangements, send the call to IXC A, with the TNS
   parameter specifying IXC B. This requests IXC A to hand the call to
   IXC B.

   Also in North America, carrier selection procedures allow a caller
   to presubscribe to a particular IXC, and further to casually dial on
   a per call basis yet a different IXC to be used. Based on business
   arrangements, the carrier which will actually carry the call may be
   different from the presubscribed or dialed carrier. In ANSI ISUP,
   the Carrier Identification Parameter (CIP) is used to convey the
   dialed or presubscribed carrier, and accordingly the value of the
   CIP parameter may differ from that of any included TNS parameter.
   The definition of a separate parameter for this in ANSI ISUP
   underscores the need to separately identify the dialed or
   presubscribed carrier from the carrier which actually routes the
   call.


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   Both [RFC3398] and [T1679] discuss interworking between the "cic"
   tel URI parameter and the ISUP TNS and/or CIP parameters. This
   document points out that there are issues with both these
   specifications, but does not attempt to resolve those issues here.

   [RFC3398] provides guidance on mapping between the "cic" tel URI
   parameter and the corresponding ISUP parameter. It essentially
   states that "cic" maps to TNS except for North American networks,
   where ANSI ISUP is used, where it maps to CIP, also allowing for
   application of local policy.

   Some information not discussed in [RFC3398] includes the fact that
   for North American networks it is not an either/or choice between
   inclusion of TNS and CIP, that both ISUP parameters may be present,
   that their values may differ, the nature of the relationship between
   these parameters, or what to do in the ISUP to SIP direction when
   both TNS and CIP are present. Also, for a given "cic" parameter
   received by the gateway, and depending on the outgoing PSTN
   interface type, a TNS value may also need to be determined and
   populated in the outgoing IAM, in addition to the CIP parameter.

   [T1679] specifies a mapping between the ISUP TNS parameter and the
   "cic" parameter in the Request-URI for North American networks. In
   doing so, it precludes the use of the "cic" parameter to convey the
   identity of the dialed or presubscribed carrier for PSTN
   interworking scenarios, as is suggested in [RFC4694], [DAI], and
   [RFC3398] for North American networks. Also, when the "cic"
   parameter is used to convey TNS for PSTN interworking scenarios,
   then if the "cic" parameter were also to be used to convey the
   dialed or presubscribed carrier for SIP originated calls, there is a
   potential for ambiguity regarding the meaning of a received "cic"
   parameter.

   The Carrier Selection Information (CSI) ISUP parameter indicates how
   the IXC identified in the CIP parameter was selected. For example,
   it may be the caller's presubscribed carrier, or may have been
   casually dialed, etc. The "dai" tel URI parameter described in [DAI]
   is intended to convey this information in SIP.

   The signaling of carrier selection information for non interworked,
   all-SIP calls in North American networks is for further study.








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9.13. Transit Network Selection

   As indicated above, the TNS identifies the IXC to which a call is to
   be routed. Note that it does not identify the network in which the
   call will actually terminate. The TNS is used in cases where it is
   necessary to specify the specific IXC through which the call should
   be routed. One example is when a call is handed off via an AT which
   provides access to multiple IXCs, in this case it is necessary to
   identify the desired IXC to the AT. Another example is when business
   arrangements dictate that the call be handed off to one IXC, which
   hands the call off to yet another specified IXC. For example, a call
   may be handed to IXC A with the TNS identifying IXC B; in this case
   the TNS instructs IXC A to hand off the call to Carrier B.

   The domain of a SIP URI in the Request-URI of a SIP INVITE can be
   seen to fill a role analogous to that of the TNS. If one provider
   needs to route a call to a specific provider, it would populate the
   domain in the Request-URI with the domain of that specific provider.
   When the call reaches that specific provider, it is typically
   (though not always) sent to a different provider to terminate the
   call. The analog to the example in the previous paragraph would be
   for a SIP provider to hand an INVITE to SIP Provider A with the
   domain in the Request-URI identifying SIP Provider B. As in the
   previous example, the signaling would reflect business arrangements.

   One potential mechanism for interworking for North America between
   the ISUP TNS and SIP is to map between TNS and a SIP domain
   representing the provider identified in the TNS. Mappings between
   TNS values and corresponding SIP domains would need to be pre-
   established and maintained at gateways implementing this mechanism.
   When such a gateway receives an ISUP IAM containing a TNS parameter,
   it would populate the domain of the Request-URI of the corresponding
   SIP INVITE with the appropriate domain mapped from the received TNS
   value. Conversely, when a gateway implementing this mechanism
   receives a SIP INVITE, the domain of the SIP URI would be consulted
   by the gateway and potentially mapped to any included TNS value.
   Note that the inclusion of a TNS value is dependent upon local
   policy, which may be determined from several factors including the
   provisioned characteristics of the trunk group via which the call is
   routed.

   Note that this mechanism precludes the use of tel URIs in the
   Request-URI for calls involving IXCs; such URIs, including their
   parameters, would need to be converted to SIP URIs as described in
   [RFC3966].




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   For SIP originated calls, the domain of the Request-URI is already
   used to identify the provider to which the request should be routed,
   thus there is no need to for additional SIP signaling to express
   such information.



9.14. Carrier Identification

   In the current PSTN in North America, callers can specify the IXC
   they want to use for a particular long distance call. Otherwise,
   their presubscribed IXC is used. In either case the carrier
   identification code (CIC) of the chosen carrier is signaled. In ANSI
   ISUP this is signaled in the Carrier Information Parameter (CIP).
   Per [RFC3398], for interworking from ANSI ISUP to SIP, the CIP is
   mapped to the "cic" tel URI parameter, and vice versa. Note that in
   North America, the CIP, which identifies the selected carrier, may
   have a different value than the TNS, and is not used for routing
   purposes.

   For SIP originated calls, the "cic" parameter can also be used to
   identify the selected carrier, as described in [RFC4694]. Note
   however that [RFC4694] describes a usage of "cic" where it is used
   for routing, which is more consistent with ITU-T ISUP than with ANSI
   ISUP, where it is not used for routing. As a result, some of the
   procedures in that document would require modification to be
   applicable to North American deployments.



9.15. Carrier Selection Information

   The ISUP Carrier Selection Information (CSI) parameter describes how
   the selected IXC was chosen; e.g. presubscribed, dialed, etc. One
   example of the utility of this information comes from Operator
   services calls that include call completion, whereby a call is
   initiated on behalf of the caller. In order to know which IXC to
   use, and how that IXC was chosen, the operator services provider
   needs to receive the CIP and Carrier Selection Information. In ANSI
   ISUP this describes the carrier identified in the CIP; while in ITU-
   T ISUP it describes the carrier identified in the TNS. Thus in both
   cases it describes the selection of the carrier identified in the
   "cic" tel URI parameter of the Request-URI.

   When interworking from ISUP to SIP, this information is included in
   the encapsulated ISUP. The "dai" parameter proposed in [DAI] can
   also be used to be carry this information. The "dai" parameter can


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   also be used for SIP originated calls. Thus, the dai information
   would be associated with the carrier identified in the ANSI CIP or
   the ITU-T TNS. That is, in the ANSI model, it is associated with the
   carrier information that is delivered to the interested
   application(s) rather than the information that is used for routing.



9.16. Passing Whisper

   During front end automation, the OIS-MS will record and may time
   compress the caller's perhaps meandering speech into what is known
   as the "whisper". This is intended to be played into a human
   operator's ear, should the call be referred to an operator, to avoid
   the operator from having to prompt the caller again. The whisper is
   obtained during the front end automation, and saved to an audio
   file.

   If the call needs to be transferred to a human operator, the whisper
   will need to be played to the operator at the same time or slightly
   prior to connecting the caller to the operator. Thus, the operator
   workstation needs to be able to access the whisper file.

   When the OIS-MS performs front end automation, it generates the
   whisper and saves it as an audio file. The location, storage type,
   and format are out of the scope of this document. What is needed is
   a way for the OIS-MS to convey the whisper information to the OIS-
   AS, so it could potentially be used for later processing, such as
   passing to a human operator.

   Due to size constraints, it may not be feasible or desirable to pass
   the actual audio file containing the whisper. This document will
   discuss the most general case of passing a pointer, in the form of a
   URI, to the audio content. What follows is a description of one
   possible way to implement this. The work of the recently formed IETF
   MEDIACTRL working group may provide alternatives.

   Since the whisper is an output of the front end automation process,
   it makes sense to return this upon completion of that process. The
   most reasonable time to do this is when the OIS-MS sends the BYE.

   Any SIP request, including BYE, can contain a message body.
   [RFC4483] defines an extension to the URL MIME External-Body Access-
   Type to satisfy the content indirection requirements for SIP. These
   extensions are aimed at allowing any MIME part in a SIP message to
   be referred to indirectly via a URI.



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   This is illustrated in the following figure. Note that the proxy has
   been omitted for clarity, as have some messages not crucial to
   illustrating the use of this mechanism. All SIP signaling traverses
   the proxy.

     AS             MS          Operator
      |              |              |
      |              |              |
      |              |              |
      |(1) INVITE    |              |
      |------------->|              |
      |              |              |
      |(2) 200 OK    |              |
      |<-------------|              |
      |(3) ACK       |              |
      |------------->|              |
      |              |              |
      |MS prompts user, collects whisper
      |              |              |
      |              |              |
      |(4) BYE, body w. status, whisper URI
      |<-------------|              |
      |              |              |
      |(5) 200 OK    |              |
      |------------->|              |
      |              |              |
      |(6) INVITE w. whisper URI    |
      |---------------------------->|
      |              |              |
      |(7) 200 OK SDP|              |
      |<----------------------------|
      |(8) ACK       |              |
      |---------------------------->|
      |              |              |
      |              |              |

            Figure 7 Call flow illustrating passing of whisper



   1. INVITE AS->MS
   INVITE sip:da@ms-1.oisp-c.example.com SIP/2.0
   [remainder of message omitted]






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   2. 200 OK MS->AS
   SIP/2.0 200 OK
   [remainder of message omitted]


   4. BYE MS->AS
   BYE sip:as-1@as-1.oisp-c.example.com SIP/2.0
   [non relevant portions of message omitted]
   Content-Type: message/external-body; access-type="URL";
       URL="http://ms1.oisp-c.example.com/whisper/20070206092700-
   0001.wav"
       expiration="Tues, 06 Feb 2007 09:30:00 GMT";
   <CRLF>
   Content-Type: audio/x-wav
   Content-Disposition: render
   <CRLF>



   5. 200 OK AS->MS
   SIP/2.0 200 OK
   [remainder of message omitted]


   6. INVITE AS->Operator Workstation
   INVITE sip:operator@operator-123.oisp-c.example.com SIP/2.0
   [non relevant portions of message omitted]
   Content-Type: message/external-body; access-type="URL";
       URL="http://ms1.oisp-c.example.com/whisper/20070206092700-
   0001.wav"
       expiration="Tues, 06 Feb 2007 09:30:00 GMT";
   <CRLF>
   Content-Type: audio/x-wav
   Content-Disposition: render
   <CRLF>


   7. 200 OK Operator->AS
   SIP/2.0 200 OK
   [remainder of message omitted]


   Note that this same mechanism also supports the case where front end
   automation is performed by one provider, and another provider
   provides the operator assistance. In this type of scenario,
   provisions need to made such that the second provider can access the
   resources referenced by the URI.


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9.17. Calling Equipment Capabilities and Characteristics

   It may be necessary for the OIS provider to learn the capabilities
   and characteristics of the caller's equipment. This would be useful
   when the OIS provider wishes to provide content to the caller other
   than that which was used on the call to the OISP. For example, the
   OIS provider might wish to send listing information via text
   message, or play a video clip about a particular venue about which
   he has requested information.

   [RFC3840] Indicating User Agent Capabilities in the Session
   Initiation Protocol (SIP), defines mechanisms by which a UA can
   convey its capabilities and characteristics to other user agents and
   to the registrar for its domain. This information is conveyed as
   parameters of the Contact header field.

   This information might be included in the incoming INVITE to the
   OISP, if the caller's UA supports this mechanism and is configured
   to do so. Otherwise, the OISP could query the caller's UA by sending
   a SIP OPTIONS request, and the UA, if it supports this mechanism,
   would include its capability feature tags in the response to the
   OISP.

   The following is an example of an INVITE containing capability
   feature tags, as it arrives at the OISP. In this case, the UA
   supports audio, video, and text. Other included tags provide
   additional information.




















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   INVITE sip:da@provider-c.example.com SIP/2.0
   Via: SIP/2.0/UDP proxy-b.provider-b.example.com:5060
   ;branch=y9hG4bK74bf9
   Via: SIP/2.0/UDP proxy-a.provider-a.example.com:5060
   ;branch=x9hG4bK74bf9
   Via: SIP/2.0/UDP client.provider-a.example.com:5060
   ;branch=z9hG4bK74bf9
   From: <sip:7327581234@provider-a.example.com>;tag=1234567
   To: 411 <tel:+411>
   Contact: <sip:7327581234@provider-a.example.com>;audio;video;text
        ;actor="principle";automata;mobility="fixed"
        ;methods="INVITE,BYE,OPTIONS,ACK,CANCEL"
   P-Asserted-Identity: "7327581234" <sip:73237581234@provider-
   a.example.com>
   P-Asserted-Identity: tel:+7327581234
   Content-Type: application/sdp
   Content-Length: ...
   [SDP not shown]


   If the OISP wishes to query the UA, it can send an OPTIONS request
   to the UA, and the UA, if it supports this mechanism, would include
   the feature capability tags in the Contact header, as show above, in
   the 200 OK response.



9.18. Media Server Returning Data to the Application Server

   The OIS-AS needs to know the outcome of the operations performed by
   the OIS-MS, e.g. success/failure of front end automation, etc. Some
   mechanism is needed to convey this information. This could be
   conveyed using non SIP mechanisms.

   Any SIP message, including BYE, can carry message bodies. The
   simplest way for a OIS-MS to return data to an OIS-AS is to
   encapsulate the data in a MIME body. This requires agreement between
   both sides on the format and semantics of these bodies.

   Another approach is to use the content indirection mechanism to
   point to the data, however this may be rather cumbersome if only a
   small amount of data is to be returned.

   Some OIS service may make use of VoiceXML, whereby the OIS-AS
   invokes VoiceXML scripts on the OIS-MS, and the OIS-MS returns data
   to the OIS-AS. [RFC5552] describes a SIP interface to VoiceXML media
   services, which is commonly employed between application servers and


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   media servers offering VoiceXML processing capabilities. This may be
   found useful for OIS services.

   The topic of application server control of media services is
   currently under study, and is the subject of the IETF MEDIACTRL
   working group's efforts.

   This information can also be conveyed using non SIP mechanisms.
   Describing such mechanisms is out of the scope of this document.



9.19. Control of Cut Through Direction for PSTN Interworking

   For PSTN interworking scenarios, it may be desirable to explicitly
   control the "duplex" of the PSTN circuit; whether it be a two way
   connection or one way in the forward direction. The rules about SDP
   offer/answer indicate that as soon as an entity sends an SDP, it
   should be prepared to receive media for that session. SDP provides a
   "mode" attribute with values such as "a=sendonly", "a=recvonly",
   "a=sendrecv" for explicit control of the directionality.

   This mode attribute can be included in the SDP sent toward the PSTN
   GW in order to signal what duplex and directionality is desired. If
   it's desired to have a talk path only in the backward direction,
   such that audio is sent toward the caller but not in the opposite
   direction, then SDP with "a=sendonly" can be sent to the GW. When
   it's desired to have both-way cut through, an updated SDP can be
   sent with "a=sendrecv". This should affect not only the duplex of
   the voice path but also the related PSTN signaling sent by the GW
   towards the PSTN switch. For example, with ISUP, the GW should send
   an ACM with the User Network Interaction bit set in the Optional
   Backward Call Indication. Existing standards on PSTN interworking do
   not address this aspect of gateway behaviour.



9.20. With Holding of Final Responses

   Currently in the PSTN, for operator services, signaling of Answer,
   whether this be an ISUP ANM or MF Answer Supervision, is often with
   held, leaving the call in an alerting state while the caller
   interacts with the operator services system. The motivation for this
   is that in the PSTN, billing normally starts when answer is
   signaled. For some calls answer may never be signaled; in others it
   may be signaled for instance when a call completion call is
   answered.


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   The equivalent of answer indication in SIP is the 200 OK final
   response. It is not an intrinsic property of SIP based systems that
   billing must start upon 200 OK. In cases where it's desired to
   emulate the PSTN behaviour, the 200 OK can be with held. When this
   is done, normal SIP procedures need to be followed to prevent the
   session from timing out. For example, the UAS can periodically
   retransmit non-100 provisional responses as described in Section
   13.3.1.1 of [RFC3261].



10. Example Call Flow - Directory Assistance

10.1. Basic Flow

   The following call flow provides examples of how a DA service could
   be implemented using the mechanisms described in this document. It
   is intended to illustrate the intended use of the proposed signaling
   mechanism. Some messages not crucial to this may be omitted for
   clarity.





























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   Caller    Proxy A   Proxy B   Proxy C   OIS-AS    OIS-MS1
      |         |         |         |         |         |
      |         |         |         |         |         |
      |         |         |         |         |         |
      |(1) INVITE tel:411 |         |         |         |
      |-------->|         |         |         |         |
      |         |         |         |         |         |
      |         |(2) INVITE sip:da@prov-b.example.com |         |
      |         |-------->|         |         |         |
      |         |         |         |         |         |
      |         |         |(3) INVITE sip:da@prov-c.example.com |
      |         |         |-------->|         |         |
      |         |         |         |         |         |
      |         |         |         |(4) INVITE sip:da-cc@prov-
   c.example.com
      |         |         |         |-------->|         |
      |         |         |         |         |         |
      |         |         |         |         |(5) INVITE prompt &
   collect
      |         |         |         |         |-------->|
      |         |         |         |         |         |
      |         |         |         |         |(6) 200 OK w.SDP
      |         |         |         |         |<--------|
      |         |         |         |         |(7) Ack  |
      |         |         |         |         |-------->|
      |         |         |         |         |         |
      |         |         |         |(8) 200 OK w.SDP   |
      |         |         |         |<--------|         |
      |         |         |         |(9) Ack  |         |
      |         |         |         |-------->|         |
      |         |         |         |         |         |
      |         |         |(10) 200 OK w.sdp  |         |
      |         |         |<--------|         |         |
      |         |         |(11) Ack |         |         |
      |         |         |-------->|         |         |
      |         |         |         |         |         |
      |         |(12) 200 OK w.sdp  |         |         |
      |         |<--------|         |         |         |
      |         |(13) Ack |         |         |         |
      |         |-------->|         |         |         |
      |         |         |         |         |         |
      |(14) 200 OK w.sdp  |         |         |         |
      |<--------|         |         |         |         |
      |(15) Ack |         |         |         |         |
      |-------->|         |         |         |         |


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      |         |         |         |         |         |
      |         |         |         |         |         |
      |         |         |         |         |         |


                       Figure 8 DA Call flow, part 1



   For brevity, only relevant SIP headers will be shown. The following
   test refers to Figure 8.

   The user, homed in provider A, initiates a request for an OIS
   service, for instance by dialing "411". The user's UA sends a SIP
   INVITE. It might contain a "tel" URI.

   1. INVITE UE -> Home Proxy

   INVITE tel:+411 SIP/2.0
   Via: SIP/2.0/UDP client.provider-a.example.com:5060
   ;branch=z9hG4bK74bf9
   From: <sip:7327581234@provider-a.example.com>;tag=1234567
   To: 411 <tel:+411>
   Contact: <sip:7327581234@provider-a.example.com>
   Content-Type: application/sdp
   Content-Length: ...


   The home provider knows nothing of OISP services, for instance it
   might be a rather small scale provider. It is essentially set up to
   forward all calls of this type to Provider B. It translates the
   Request-URI to a SIP URI and sends the call on to provider B.
   Because of this retargeting, it adds a History-Info header to
   capture the dialed digits.

   The caller's identity is verified in a manner consistent with this
   provider's policies, and the proxy adds two P-Asserted-Identity
   headers: one with a SIP URI, and another with a "tel" URI.











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   2. INVITE proxy-a -> proxy-b

   INVITE sip:411@provider-b.example.com SIP/2.0
   Via: SIP/2.0/UDP proxy-a.provider-a.example.com:5060
   ;branch=x9hG4bK74bf9
   Via: SIP/2.0/UDP client.provider-a.example.com:5060
   ;branch=z9hG4bK74bf9
   From: <sip:7327581234@provider-a.example.com>;tag=1234567
   To: 411 <tel:+411>
   Contact: <sip:7327581234@provider-a.example.com>
   P-Asserted-Identity: "7327581234" <sip:73237581234@provider-
   a.example.com>
   P-Asserted-Identity: tel:+7327581234
   History-Info: <tel: +411>; index=1
   Content-Type: application/sdp
   Content-Length: ...


   Proxy-b in provider-b's network receives the request. This is a
   larger network, and it has business relationships with several OIS
   providers, as well as with several providers which serve
   subscribers. This provider has logic which requires it to query the
   Home Provider's network to find some information related to the
   caller. This is not likely to be a SIP related function, and is thus
   out of scope for this document. The logic executes, taking the
   result of this query into account. It is determined that the call is
   for directory assistance, and that the call should be routed to
   provider C for handling.

   So, proxy-b retargets the Request-URI to reflect this, and routes
   the call to provider C (the OISP). It adds another entry to the
   History-Info header to capture this retargeting.

















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   3. INVITE proxy-b -> proxy-c

   INVITE sip:da@provider-c.example.com SIP/2.0
   Via: SIP/2.0/UDP proxy-b.provider-b.example.com:5060
   ;branch=y9hG4bK74bf9
   Via: SIP/2.0/UDP proxy-a.provider-a.example.com:5060
   ;branch=x9hG4bK74bf9
   Via: SIP/2.0/UDP client.provider-a.example.com:5060
   ;branch=z9hG4bK74bf9
   From: <sip:7327581234@provider-a.example.com>;tag=1234567
   To: 411 <tel:+411>
   Contact: <sip:7327581234@provider-a.example.com>
   P-Asserted-Identity: "732758123" <sip:73237581234@provider-
   a.example.com>
   P-Asserted-Identity: tel:+7327581234
   History-Info: <tel: +411>; index=1, <sip:da@provider-a.example.com>;
   index=2
   Content-Type: application/sdp
   Content-Length: ...


   Proxy-c in provider C's network receives the request. The source of
   the request is authenticated via mechanisms not described here. It
   needs to know how to bill this call, and thus needs to know which
   provider it came from. It looks at the topmost Via header, and sees
   that the call came from provider B.

   It examines the History-Info header, and is able to identify the
   dialed digits. It can also determine from the SIP URI which domains
   have been traversed, as long as each has retargeted and appended an
   entry in the header.

   The proxy determines that the call needs to go the OIS-AS for
   handling, so it retargets if necessary and forwards the INVITE.

   The OIS-AS performs 3PCC. It determines that the call needs a
   branded announcement based on the identity of the home provider,
   which it derives from the P-Asserted-Identity header. It initiates a
   new call leg toward OIS-MS1 for front end automation. Per [RFC4240],
   the "dialog" portion of the Request-URI indicates the "prompt &
   collect" service. The URI identifies the VoiceXML script to be
   executed. The SDP is the caller's SDP.







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   5. INVITE OIS-AS -> MS1

   INVITE sip:dialog@ois-as.prov-c.example.com; \
          voicexml=http://vxmlserver.example.net/cgi-bin/script.vxml \
   SIP/2.0
   Via: SIP/2.0/UDP ois-as.prov-c.example.com:5060
   ;branch=z9hG4bK74bf9
   From: <sip:ois-as@ois-as.prov-c.com>;tag=1234567
   To: sip:dialog@ois-as.prov-c.example.com; \
          voicexml=http://vxmlserver.example.net/cgi-bin/script.vxml
   Contact: <sip:ois-as@ois-as.prov-c.example.com>
   Content-Type: application/sdp
   Content-Length: ...

   The OIS-MS responds with a 200 OK, with its own SDP. The OIS-AS now
   sends a 200 OK response back toward the caller, with the MS's SDP.
   Note that the OIS-AS could first have sent non final response back
   toward the user.






























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   Caller    OIS-AS    OIS-MS1     ACD       OWS
      |         |         |         |         |
      |(16) RTP session   |         |         |
      |...................|         |         |
      |         |         |         |         |
      |         |(17) INFO w.URI, body        |
      |         |<--------|         |         |
      |         |         |         |         |
      |         |(18) INVITE        |         |
      |         |------------------>|         |
      |         |         |         |         |
      |         |(19) 182 Queued    |         |
      |         |<------------------|         |
      |         |         |         |         |
      |         |(20) 3xx Redirection         |
      |         |<------------------|         |
      |         |         |         |         |
      |         |(21) INVITE        |         |
      |         |---------------------------->|
      |         |         |         |         |
      |         |(22) 200 OK        |         |
      |         |<----------------------------|
      |         |(23) ACK |         |         |
      |         |---------------------------->|
      |         |         |         |         |
      |         |(24) BYE |         |         |
      |         |-------->|         |         |
      |         |(25) 200 OK        |         |
      |         |<--------|         |         |
      |         |         |         |         |
      |(26) re INVITE     |         |         |
      |<--------|         |         |         |
      |         |         |         |         |
      |(27) 200 OK        |         |         |
      |-------->|         |         |         |
      |(28) ACK |         |         |         |
      |<--------|         |         |         |
      |         |         |         |         |
      |(29) RTP session   |         |         |
      |.......................................|
      |         |         |         |         |
      |         |(30) BYE |         |         |
      |         |<----------------------------|
      |         |(31) 200 OK        |         |
      |         |---------------------------->|



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                       Figure 9 DA Call flow, part 2



   The following text refers to Figure 9.

   The user is now connected (16) to the MS, which plays a branded
   announcement, and prompts for the listing information. When the user
   speaks his request, the MS processes the audio to obtain a "whisper"
   file, or condensed version of the request. In this example, the MS
   is unable to successfully perform the query, so it sends an
   indication of this to the AS. In this example, the indication is
   sent using an as yet unspecified protocol message carried in a
   message body in a SIP INFO message, which also carries a URI which
   points to the whisper file. Other mechanisms, including non SIP
   mechanisms, could also be used to this end (this is the subject of
   further study). The AS allows the caller to remain connected to the
   MS while it sets up a call to an operator workstation (OWS),
   allowing for the possibility to play custom announcements to the
   caller.

   The OIS-AS decides based on the failure indication that it needs to
   route the call to a human operator. It sends an INVITE (18) to the
   ACD server. This INVITE carries information about the required
   characteristics, such as language and skill set, of the operator
   which should be selected for this call. The means by which this
   information is carried has yet to be defined. One possible way an
   ACD could be implemented is as a presence server, such that it keeps
   track of the availability of all the operators. The Media Resource
   Broker being discussed in the IETF MEDIACTRL working group also
   represents an approach to ACD.

   If the call needs to be queued due to lack of an immediately
   available resource, the ACD may send a 812 Queued response (19). In
   this example, the ACD server is implemented as a redirect server -
   it sends a 3XX response (20) which identifies the operator the OIS-
   AS should contact. Alternately, the ACD server could have proxied
   the request to the operator.

   The OIS-AS now sends an INVITE (21) containing the URI to the
   whisper, as well as the caller's SDP, to the indicated operator
   workstation. The operator workstation sends a 200 OK (22) with its
   SDP, which the OIS-AS sends toward the caller in a re-INVITE (26).
   Only when the workstation has sent a final response to the INVITE,
   the AS sends a BYE (24) to the MS.




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   The caller is now connected to the operator (29), and the operator
   helps the caller with the listing. The operator workstation launches
   a query, and a response is received. The operator signals a BYE (30)
   toward the OIS-AS, which may contain the listing information in a
   message body, a pointer (URI) to the listing information, or it may
   pass this information to the OIS-AS using some other, non SIP
   mechanism.


   Caller    OIS-AS    OIS-MS2
      |         |         |
      |         |         |
      |         |         |
      |         |(32) INVITE
      |         |-------->|
      |         |         |
      |         |(33) 200 OK
      |         |<--------|
      |         |(34) ACK |
      |         |-------->|
      |         |         |
      |(35) re INVITE     |
      |<--------|         |
      |         |         |
      |(36) 200 OK        |
      |-------->|         |
      |(37) ACK  |        |
      |<--------|         |
      |         |         |
      |(38) RTP session   |
      |...................|
      |         |         |
      |         |(39) BYE w.URI, body
      |         |<--------|
      |         |         |
      |         |(40) 200 OK
      |         |-------->|
      |         |         |
      |(41) REFER         |
      |<--------|         |
      |         |         |
      |         |         |


                      Figure 10 DA Call flow, part 3




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   The following text refers to Figure 10.

   The OIS-AS sends an INVITE (32) to another OIS-MS, MS2, for back end
   automation. (Note that though MS2 is shown as a separate element,
   the functionality it provides may or may not require a separate
   element.) When it receives MS2's SDP in the 200 OK (33), it sends a
   re-INVITE (35) toward the user to update the SDP. At this point an
   audio session is in place between the caller and the back end
   automation MS (38). The MS plays the listing information, and offers
   call completion service. The caller accepts, so OIS-MS2 sends a BYE
   (39) with a message body containing the result of the call
   completion offer. Since call completion was requested, the OIS-AS
   sends a REFER (41) to the caller, to cause it to place a call to the
   listed party. The OIS-AS may or may not care about subsequent
   NOTIFYs from the caller, and drops out of the call.


10.2. OISP Drops Out at Call Completion Setup

   The OISP may want to support different call flow options with
   respect to call completion. Reasons for this may include the desire
   to free up resources quickly, provide additional functionality, etc.
   When the OISP wants to provide the listing information and free
   resources as soon as possible, a simple flow based on REFER can be
   used, as illustrated below.

   In this flow, the caller is already connected to an OISP resource
   such as an MS, and requests call completion. In (2), the OISP sends
   a REFER to initiate the call completion call. The caller's UA
   indicates acceptance of the REFER by sending a 202 Accepted (3). It
   then sends a NOTIFY indicating that it is attempting to contact the
   indicated resource, by sending an INVITE (10). When the AS receives
   this notification, it understands that the caller is attempting the
   call completion call, so it drops the call by sending BYE in (6)and
   (8). The various notifications sent by the caller to the OISP can be
   used to monitor progress of the call, or may simply be ignored from
   an application standpoints (from a protocol standpoint they must be
   acknowledged).









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   Caller           AS             MS        Called Party
      |              |              |              |
      |              |              |              |
      |(1) Caller connected to e.g., MS            |
      |.............................|              |
      |              |              |              |
      |(2) REFER (Called)           |              |
      |<-------------|              |              |
      |(3) 202 Accepted             |              |
      |------------->|              |              |
      |              |              |              |
      |(4) NOTIFY (Trying)          |              |
      |------------->|              |              |
      |(5) 200 OK    |              |              |
      |<-------------|              |              |
      |              |              |              |
      |              |(6) BYE       |              |
      |              |------------->|              |
      |              |(7) 200 OK    |              |
      |              |<-------------|              |
      |              |              |              |
      |(8) BYE       |              |              |
      |<-------------|              |              |
      |(9) 200 OK    |              |              |
      |------------->|              |              |
      |              |              |              |
      |(10) INVITE   |              |              |
      |------------------------------------------->|
      |              |              |              |
      |(11) 200 OK   |              |              |
      |<-------------------------------------------|
      |(12) Ack      |              |              |
      |------------------------------------------->|
      |              |              |              |
      |(13) NOTIFY (200 OK)         |              |
      |------------->|              |              |
      |(14) 200 OK   |              |              |
      |<-------------|              |              |
      |              |              |              |
             Figure 11 OISP Drops Out at Call Completion Setup








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10.3. OISP Drops Out After Call Completion Call is Answered

   The OISP may need to remain in the signaling path until the call
   completion call is answered. One way to implement this is to use the
   REFER method with the Replaces header, as described in [RFC3891]. In
   this case, once the call completion call is answered (5), the OISP's
   AS sends a REFER (6) toward the caller with a Replaces header
   identifying the current dialog between the AS and called party, and
   Referred-by header identifying the AS. This causes an INVITE (10) to
   be sent toward the called party, also with Replaces and Referred-by
   headers. As described in [RFC3891], this causes a new session to be
   set up with the called party, replacing the existing sessions. As
   part of this, the original session is torn down (16). Thus, the
   OISP's resources are removed from the call.

































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   Caller           AS             MS        Called Party
     |              |              |              |
     |              |              |              |
     |              |              |              |
     |(1) Caller listening to announcements, etc  |
     |.............................|              |
     |              |              |              |
     |              |(2) INVITE    |              |
     |              |---------------------------->|
     |              |              |              |
     |              |(3) 183 Ringing              |
     |              |<----------------------------|
     |              |              |              |
     |              |(4) 200 OK    |              |
     |              |<----------------------------|
     |              |              |              |
     |              |(5) ACK       |              |
     |              |---------------------------->|
     |              |              |              |
     |[Called party has answered]  |              |
     |              |              |              |
     |(6) REFER (Called Party, Replaces:AS, Referred-by:AS)
     |<-------------|              |              |
     |              |              |              |
     |(7) 202 Accepted             |              |
     |------------->|              |              |
     |              |              |              |
     |(8) NOTIFY (100 Trying)      |              |
     |------------->|              |              |
     |              |              |              |
     |(9) 200 OK    |              |              |
     |<-------------|              |              |
     |              |              |              |
     |(10) INVITE (Replaces:AS, Referred-by:AS)   |
     |------------------------------------------->|
     |              |              |              |
     |(11) 200 OK   |              |              |
     |<-------------------------------------------|
     |              |              |              |
     |(12) ACK      |              |              |
     |------------------------------------------->|
     |              |              |              |
     |[Called Party replaces existing dialog from Step 2 with new one]
     |              |              |              |
     |              |              |              |
     |(13) RTP [Called and Calling Party are now connected ]


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     |............................................|
     |              |              |              |
     |              |              |              |
     |[ Remainder of steps cleanup dialogs between Caller-AS and AS-
   Called ]
     |              |              |              |
     |(14) NOTIFY (200 OK)         |              |
     |------------->|              |              |
     |              |              |              |
     |(15) 200 OK   |              |              |
     |<-------------|              |              |
     |              |              |              |
     |              |(16) BYE (as a result of receiving Replaces)
     |              |<----------------------------|
     |              |              |              |
     |              |(17) 200 OK   |              |
     |              |---------------------------->|
     |              |              |              |
     |(18) BYE      |              |              |
     |<-------------|              |              |
     |              |              |              |
     |(19) 200 OK   |              |              |
     |------------->|              |              |
     |              |              |              |
          Figure 12 OISP Drops After Call Completion is Answered



10.4. OISP Drops Out After Interaction with Called Party

   In this scenario, the OISP needs to interact with the called party,
   then desired to remove its resources from the call. Collect calls
   are one example where this might be used. This also uses REFER with
   Replaces. The OISP places a call to the called party, and
   interactions between OISP resources (automated or human) occur. The
   OISP then sends a REFER with Replaces and Referred-by to the calling
   party, which then sends an INVITE as described for the previous
   scenario.

   In this scenario, the OISP has one media session (1) with the caller
   and another (2) with the called party. After interactions have been
   completed, the OISP initiates the transfer by sending a REFER (3)
   with Replaces and Referred-by headers. This causes the caller's UA
   to send a corresponding INVITE (7) containing those headers. As with
   the previous scenario, this causes initiation of a new session
   replacing the existing session, as well as teardown (10) of the
   existing session.


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   Caller                AS                  MS                Called
     |                   |                   |                   |
     |                   |                   |                   |
     |                   |                   |                   |
     |[ Calling party has some RTP session with MS ]             |
     |                   |                   |                   |
     |                   |                   |                   |
     |(1) RTP            |                   |                   |
     |.......................................|                   |
     |                   |                   |                   |
     |[ Called party has different RTP session with MS ]         |
     |                   |                   |                   |
     |                   |                   |                   |
     |                   |                   |(2) RTP            |
     |                   |                   |...................|
     |                   |                   |                   |
     |[ AS initiates transfer with REFER ]   |                   |
     |                   |                   |                   |
     |                   |                   |                   |
     |(3) REFER (to called, Replaces:AS, Referred-by:AS)         |
     |<------------------|                   |                   |
     |                   |                   |                   |
     |                   |                   |                   |
     |(4) 202 Accepted   |                   |                   |
     |------------------>|                   |                   |
     |                   |                   |                   |
     |(5) NOTIFY (trying)|                   |                   |
     |------------------>|                   |                   |
     |                   |                   |                   |
     |(6) 200 OK         |                   |                   |
     |<------------------|                   |                   |
     |                   |                   |                   |
     |[ Replaces header causes Called to replace old call with new ]
     |                   |                   |                   |
     |                   |                   |                   |
     |(7) INVITE (Replaces:AS, Referred-by:AS)                   |
     |---------------------------------------------------------->|
     |                   |                   |                   |
     |                   |                   |                   |
     |(8) 200 OK (SDP-called)                |                   |
     |<----------------------------------------------------------|
     |                   |                   |                   |
     |(9) ACK            |                   |                   |
     |---------------------------------------------------------->|
     |                   |                   |                   |
     |[ Calling and Called are now talking directly ]            |


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     |                   |                   |                   |
     |                   |                   |                   |
     |                   |                   |                   |
   |[As a result of Replaces operation, called ends session with MS]
     |                   |                   |                   |
     |                   |(10) BYE (as a result of processing Replaces)
     |                   |<--------------------------------------|
     |                   |                   |                   |
     |                   |(11) 200 OK        |                   |
     |                   |-------------------------------------->|
     |                   |                   |                   |
     |[AS ends session with Calling]         |                   |
     |                   |                   |                   |
     |(12) BYE           |                   |                   |
     |<------------------|                   |                   |
     |(13) 200 OK        |                   |                   |
     |------------------>|                   |                   |
     |                   |                   |                   |
     |(14) NOTIFY (200 OK)                   |                   |
     |------------------>|                   |                   |
     |(15) 200 OK        |                   |                   |
     |<------------------|                   |                   |
     |                   |                   |                   |
       Figure 13 OISP Drops Out After Interaction With Called Party



10.5. OISP Remains in Path

   In some cases, the OISP desires to maintain its elements in the
   signaling path and possibly in the media path as well for the
   duration of the call completion call. One possible reason for doing
   this is so that the caller can request to be returned to the OISP
   for additional services after the call has completed.

   The figure below begins with the caller already connected to OISP
   resources. The AS initiates call completion in steps 2 through 5 by
   sending an INVITE toward the called party. The AS then sends a re-
   INVITE toward the caller to update the SDP, and step 9 shows the
   media session established between the caller and the called party,
   and in step 10 clears the previous session with the MS. When the
   called party hangs up in step 12, the AS responds. In step 14, the
   AS has the opportunity to redirect the caller to a MS or other
   resource to offer additional services, but in this case simply
   clears the dialog with the caller.




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   Caller           AS             MS        Called Party
      |              |              |              |
      |              |              |              |
      |              |              |              |
      |(1) Caller has media session with MS        |
      |.............................|              |
      |              |              |              |
      |AS initiates call completion |              |
      |              |              |              |
      |              |              |              |
      |              |(2) INVITE    |              |
      |              |---------------------------->|
      |              |              |              |
      |              |(3) 180 Ringing              |
      |              |<----------------------------|
      |              |              |              |
      |              |(4) 200 OK    |              |
      |              |<----------------------------|
      |              |              |              |
      |              |(5) ACK       |              |
      |              |---------------------------->|
      |              |              |              |
      |Called party has answered    |              |
      |              |              |              |
      |              |              |              |
      |(6) re-INVITE |              |              |
      |<-------------|              |              |
      |              |              |              |
      |(7) 200 OK    |              |              |
      |------------->|              |              |
      |              |              |              |
      |(8) ACK       |              |              |
      |<-------------|              |              |
      |              |              |              |
      |(9) Media Session            |              |
      |............................................|
      |              |              |              |
      |              |(10) BYE      |              |
      |              |------------->|              |
      |              |              |              |
      |              |(11) 200 OK   |              |
      |              |<-------------|              |
      |              |              |              |
      |Called party hangs up        |              |
      |              |              |              |
      |              |              |              |
      |              |(12) BYE      |              |


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      |              |<----------------------------|
      |              |              |              |
      |              |(13) 200 OK   |              |
      |              |---------------------------->|
      |              |              |              |
      |AS clears call back to Caller|              |
      |              |              |              |
      |              |              |              |
      |(14) BYE      |              |              |
      |<-------------|              |              |
      |              |              |              |
      |(15) 200 OK   |              |              |
      |------------->|              |              |
      |              |              |              |
      |              |              |              |
                 Figure 14 OISP Remains in Signaling Path


10.6. Return of Call to OISP

   In some cases, it is desirable that the caller be able to request,
   typically via keypad stimulus such as the octothorpe or pound sign,
   to be returned to the OISP operator (human or automated). One way
   this can be accomplished is for the OISP to use KPML [RFC4730] to
   subscribe to the desired keypress. The flow presented here assumes
   that the calling UA, or an intermediary acting on its behalf,
   supports this event package, and is able to detect the desired
   keypress. Examples of such intermediaries include back to back user
   agents (B2BUAs) and Session Border Controllers (SBCs). Another
   option is for the OISP to insert some element such as a MS into the
   media stream, which is capable of detecting and notifying the
   desired keypress.

   In (1) the caller has already been connected to called party via the
   AS. In (2), the AS subscribes to KPML events from the caller's UA.
   Note that in some environments, this could be intercepted and acted
   upon by intermediaries such as B2BUAs or SBCs. As long as this does
   not interfere with notification, this is transparent to the OISP.
   When the caller presses the specified keypress to request return to
   the OISP, a NOTIFY (6) is sent to the AS. At this time, the OISP can
   perform whatever actions are necessary, such as perhaps sending a
   re-INVITE or UPDATE to move the media session to an OISP resource.







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   Caller           AS             MS        Called Party
       |              |              |              |
       |(1) Caller connected to called via 3PCC     |
       |............................................|
       |              |              |              |
       |(2) SUBSCRIBE (KPML body specifying "#")    |
       |<-------------|              |              |
       |(3) 200 OK    |              |              |
       |------------->|              |              |
       |              |              |              |
       |(4) NOTIFY (result of subscription)         |
       |------------->|              |              |
       |(5) 200 OK    |              |              |
       |<-------------|              |              |
       |              |              |              |
       |[ Some time passes ]         |              |
       |              |              |              |
       |[ Caller wants back to OISP, hits "#" ]     |
       |              |              |              |
       |              |              |              |
       |(6) NOTIFY (KPML body specifying "#")       |
       |------------->|              |              |
       |(7) 200 OK    |              |              |
       |<-------------|              |              |
                     Figure 15 Return of Call to OISP



10.7. PSTN Origination

   The following example shows a call from a PSTN caller. In this case,
   the incoming IAM is translated at the PSTN gateway to a SIP INIVTE.
   Though not specifically shown, the INVITE contains the IAM
   encapsulated in a MIME body, and any ISUP parameters are mapped to
   SIP headers and/or parameters as described in [T1679]; additionally
   the mechanisms described in this document are also applied, such as
   encoding of the trunk group information in the Contact header per
   [RFC4904].











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   EO          GW          AS          MS1         MS2    Called Party
    |           |           |           |           |           |
    |           |           |           |           |           |
    |           |           |           |           |           |
    |Incoming ISUP Call     |           |           |           |
    |           |           |           |           |           |
    |(1) IAM    |           |           |           |           |
    |---------->|           |           |           |           |
    |           |(2) INVITE (GW SDP)    |           |           |
    |           |---------->|           |           |           |
    |           |           |(3) INVITE (GW SDP)    |           |
    |           |           |---------->|           |           |
    |           |           |(4) 200 OK (MS1 SDP)   |           |
    |           |           |<----------|           |           |
    |           |           |(5) ACK    |           |           |
    |           |           |---------->|           |           |
    |           |(6) 183 Session Progress (MS1 SDP) |           |
    |           |<----------|           |           |           |
    |(7) ACM    |           |           |           |           |
    |<----------|           |           |           |           |
    |           |(8) PRACK  |           |           |           |
    |           |---------->|           |           |           |
    |           |(9) 200 OK |           |           |           |
    |           |<----------|           |           |           |
    |           |(10) RTP Session       |           |           |
    |           |.......................|           |           |
    |E.g. Front End Announcements       |           |           |
    |           |           |           |           |           |
    |           |           |(11) BYE   |           |           |
    |           |           |<----------|           |           |
    |           |           |(12) 200 OK|           |           |
    |           |           |---------->|           |           |
    |           |           |           |           |           |
    |           |           |(13) INVITE (GW SDP)   |           |
    |           |           |---------------------->|           |
    |           |           |(14) 200 OK (MS2 SDP)  |           |
    |           |           |<----------------------|           |
    |           |           |(15) ACK   |           |           |
    |           |           |---------------------->|           |
    |           |(16) UPDATE (MS2 SDP)  |           |           |
    |           |<----------|           |           |           |
    |           |(17) 200 OK|           |           |           |
    |           |---------->|           |           |           |
    |           |(18) RTP Session       |           |           |
    |           |...................................|           |
    |           |           |(19) INVITE|           |           |
    |           |           |---------------------------------->|


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    |           |           |(20) 183 Session Progress          |
    |           |           |<----------------------------------|
    |           |           |(21) PRACK |           |           |
    |           |           |---------------------------------->|
    |           |           |(22) 200 OK|           |           |
    |           |           |<----------------------------------|
    |           |(23) UPDATE (Called SDP)           |           |
    |           |<----------|           |           |           |
    |           |(24) 200 OK|           |           |           |
    |           |---------->|           |           |           |
    |           |           |(25) BYE   |           |           |
    |           |           |<----------------------|           |
    |           |           |(26) 200 OK|           |           |
    |           |           |---------------------->|           |
    |           |(27) RTP Session       |           |           |
    |           |...............................................|
    |           |           |(28) 200 OK|           |           |
    |           |           |<----------------------------------|
    |           |           |(29) Ack   |           |           |
    |           |           |---------------------------------->|
    |           |(30) 200 OK|           |           |           |
    |           |<----------|           |           |           |
    |           |(31) ACK   |           |           |           |
    |           |---------->|           |           |           |
    |(32) ANM   |           |           |           |           |
    |<----------|           |           |           |           |
    |           |           |           |           |           |
                        Figure 16 PSTN Origination




10.8. PSTN Termination

   The following example shows a call which results in call completion
   to a destination on the PSTN. In Step 17 the AS sends an INVITE
   toward the PSTN gateway which results in an IAM being sent which
   initiates the PSTN call leg.











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   Calling Party    AS          MS1         MS2         GW          EO
         |           |           |           |           |           |
         |           |           |           |           |           |
         |           |           |           |           |           |
         |Incoming SIP call      |           |           |           |
         |           |           |           |           |           |
         |(1) INVITE (Caller SDP)|           |           |           |
         |---------->|           |           |           |           |
         |           |(2) INVITE (Caller SDP)|           |           |
         |           |---------->|           |           |           |
         |           |(3) 200 OK (MS1 SDP)   |           |           |
         |           |<----------|           |           |           |
         |           |(4) ACK    |           |           |           |
         |           |---------->|           |           |           |
         |(5) 183 Session Progress (MS1 SDP) |           |           |
         |<----------|           |           |           |           |
         |(6) PRACK  |           |           |           |           |
         |---------->|           |           |           |           |
         |(7) 200 OK |           |           |           |           |
         |<----------|           |           |           |           |
         |(8) RTP Session        |           |           |           |
         |.......................|           |           |           |
         |E.g. Front End Announcements       |           |           |
         |           |           |           |           |           |
         |           |(9) BYE    |           |           |           |
         |           |<----------|           |           |           |
         |           |(10) 200 OK|           |           |           |
         |           |---------->|           |           |           |
         |           |           |           |           |           |
         |           |(11) INVITE (Caller SDP)           |           |
         |           |---------------------->|           |           |
         |           |(12) 200 OK (MS2 SDP)  |           |           |
         |           |<----------------------|           |           |
         |           |(13) ACK   |           |           |           |
         |           |---------------------->|           |           |
         |(14) UPDATE (MS2 SDP)  |           |           |           |
         |<----------|           |           |           |           |
         |(15) 200 OK|           |           |           |           |
         |---------->|           |           |           |           |
         |(16) RTP Session       |           |           |           |
         |...................................|           |           |
         |           |(17) INVITE|           |           |           |
         |           |---------------------------------->|           |
         |           |           |           |           |(18) IAM   |
         |           |           |           |           |---------->|
         |           |           |           |           |(19) ACM   |
         |           |           |           |           |<----------|


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         |           |(20) 183 Session Progress          |           |
         |           |<----------------------------------|           |
         |           |(21) PRACK |           |           |           |
         |           |---------------------------------->|           |
         |           |(22) 200 OK|           |           |           |
         |           |<----------------------------------|           |
         |(23) UPDATE (GW SDP)   |           |           |           |
         |<----------|           |           |           |           |
         |(24) 200 OK|           |           |           |           |
         |---------->|           |           |           |           |
         |           |           |           |           |(25) ANM   |
         |           |           |           |           |<----------|
         |           |(26) 200 OK|           |           |           |
         |           |<----------------------------------|           |
         |           |(27) Ack   |           |           |           |
         |           |---------------------------------->|           |
         |(28) 200 OK(GW SDP)    |           |           |           |
         |<----------|           |           |           |           |
         |(29) ACK   |           |           |           |           |
         |---------->|           |           |           |           |
         |(30) RTP Session       |           |           |           |
         |...............................................|           |
         |           |           |           |           |(31) REL   |
         |           |           |           |           |<----------|
         |           |           |           |           |(32) RLC   |
         |           |           |           |           |---------->|
         |           |(33) BYE   |           |           |           |
         |           |<----------------------------------|           |
         |           |(34) 200 OK|           |           |           |
         |           |---------------------------------->|           |
         |(35) BYE   |           |           |           |           |
         |<----------|           |           |           |           |
         |(36) 200 OK|           |           |           |           |
         |---------->|           |           |           |           |
         |           |           |           |           |           |
                        Figure 17 PSTN Termination



10.9. Call Completion By Releasing Call Back to PSTN

   This example shows how when a call is received from the PSTN, call
   completion can be achieved by releasing the call back to the PSTN to
   have a PSTN switch initiate the call completion call. This allows
   call completion to occur in the PSTN, and completely drops the call
   from the OISP. The PSTN feature which supports this is called
   Release To Pivot; other implementations may also exist. The


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   gateway's connection to the PSTN needs to be specifically
   provisioned to support this feature. There is currently no standard
   describing the invocation of this feature using SIP; nor does this
   document intend to do this. Rather, it intends to illustrate one way
   in which it might be done. This flow appears as the equivalent of a
   blind transfer with the PSTN gateway as the originator; the key
   thing is that the PSTN gateway needs to understand this as a request
   for Release to Pivot or equivalent PSTN feature.









































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   EO             GW             AS             MS1           EO-2
    |              |              |              |              |
    |              |              |              |              |
    |              |              |              |              |
    |Incoming ISUP Call           |              |              |
    |              |              |              |              |
    |(1) IAM       |              |              |              |
    |------------->|              |              |              |
    |              |(2) INVITE (GW SDP)          |              |
    |              |------------->|              |              |
    |              |              |(3) INVITE (GW SDP)          |
    |              |              |------------->|              |
    |              |              |(4) 200 OK (MS1 SDP)         |
    |              |              |<-------------|              |
    |              |              |(5) ACK       |              |
    |              |              |------------->|              |
    |              |(6) 183 Session Progress (MS1 SDP)          |
    |              |<-------------|              |              |
    |(7) ACM       |              |              |              |
    |<-------------|              |              |              |
    |              |(8) PRACK     |              |              |
    |              |------------->|              |              |
    |              |(9) 200 OK    |              |              |
    |              |<-------------|              |              |
    |              |(10) RTP Session             |              |
    |              |.............................|              |
    |E.g. Front End Announcements |              |              |
    |              |              |              |              |
    |              |              |(11) BYE      |              |
    |              |              |<-------------|              |
    |              |              |(12) 200 OK   |              |
    |              |              |------------->|              |
    |              |(13) REFER (call completion number)         |
    |              |<-------------|              |              |
    |              |(14) 202 Accepted            |              |
    |              |------------->|              |              |
    |              |(15) NOTIFY(trying)          |              |
    |              |------------->|              |              |
    |              |(16) 200 OK   |              |              |
    |              |<-------------|              |              |
    |(17) REL      |              |              |              |
    |<-------------|              |              |              |
    |(18) RLC      |              |              |              |
    |------------->|              |              |              |
    |              |(19) NOTIFY(200 OK)          |              |
    |              |------------->|              |              |
    |              |(20) 200 OK   |              |              |


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    |              |<-------------|              |              |
    |(21) IAM, etc.|              |              |              |
    |---------------------------------------------------------->|
    |              |              |              |              |
    |              |              |              |              |
         Figure 18 Call Completion By Releasing Call Back to PSTN



11. Operator Services Example Call Flows

   The following call flows provide examples of how specific operator
   services could be implemented using the mechanisms described in this
   document. The purpose is to illustrate one way to implement these
   services using the proposed signaling mechanisms.

11.1. Network Controlled Coin Calls

   This flow depicts a SIP based OISP handling calls from a network
   controlled coin station. The OISP needs to determine the coinage
   deposited by the station. Note that "smart" coin stations do not
   require interaction with the OISP. This discussion only addresses
   control of TDM based network controlled coin stations.

   The configuration is as follows. Network controlled coin stations
   are connected to TDM based end offices (EOs) using special access
   lines, the characteristics of which are not important to this
   discussion. The EO exchanges signaling with the station over this
   access line, but does not perform the coin control. Operator
   Services switches historically provide the control for these types
   of calls, and the EO connects to the Operator Switch via special
   coin control trunks. The EO translates between coin access and coin
   trunk signaling.

   The signaling includes coin station control and coin deposit
   indications. The OISP uses coin station control signaling to
   instruct the station to collect coins, return coins, etc. The coin
   deposit signaling indicates the coinage inserted by the user.

   Coin deposit signaling is sent as tones on the access line and on
   the trunk. The values of these tones are described elsewhere. In
   order to convey these tones, either a new event package would need
   to be defined, or extensions to an existing event package, such as
   KPML [RFC4730].

   Coin trunks can be SS7 or MF trunks. Both of these have native
   signaling formats for conveying coin control events. PSTN gateways


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   interwork between PSTN and SIP signaling. Other than PSTN
   interworking mechanisms, there is no currently defined mechanism for
   conveying coin control events using SIP.

   One potential way to address this would be to standardize a new
   event package (or extend an existing package), so that SIP
   notification mechanisms can be used. This is subject to the level of
   IETF community interest and support.

   Since coin deposit events are conveyed over the trunk as inband tone
   bursts, this would not be covered by current PSTN interworking
   mechanisms. There is no existing protocol mechanism which can
   currently be used to convey coin deposit tones. KPML [RFC4730] is a
   potential candidate for extension; this is for further study.

   The main idea of the scheme presented here is that the OIS AS
   exchanges coin control signaling with the coin station via the PSTN
   GW, which speaks either MF or ISUP toward the end office serving the
   coin station, and speaks SIP to the AS. The PSTN GW and AS exchange
   encapsulated ISUP in SIP message bodies, which includes the ISUP SAP
   parameter, and the PSTN GW uses either ISUP or MF to communicate
   with the end office. The coin deposit signals are detected on the
   voice path by the PSTN GW, and conveyed to the AS using either
   extensions to KPML or a new SIP event package.

   Note that the only reason for exchanging encapsulated ISUP here is
   to exchange the SAP parameter. This also includes having the AS
   generate encapsulated ISUP simply so that it can convey the SAP
   information. An alternative option would be to define a MIME type
   and carry this as a body in the SIP messages instead of encapsulated
   ISUP. Generation of full ISUP messages when only the SAP parameter
   is needed requires support of a full ISUP protocol stack at the AS,
   which is otherwise unnecessary. One potential MIME media type which
   might be used to this end is the "application/nss" MIME media type
   defined in [NSS].

   In the following flow, the EO is the end office service the coin
   station, the PSTN GW is the GW terminating the voice trunks and
   signaling from the EO, the AS is the OIS AS, the MS is a media
   server in the OIS provider, and the called party is self
   explanatory.

   In step 1, the coin station (not shown) has signaled a call request
   to the EO, which in turn selects a coin trunk toward the OISP PSTN
   GW, and initiates the corresponding signaling. In steps 2 through 4,
   the PSTN GW sends an INVITE to the AS, which accepts the call.



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   In steps 5 through 7, the AS sends a SIP INFO message containing
   encapsulated ISUP, which contains an ISUP SAP parameter with the
   Feature Code Indicator (FCI) indicating "Network Service Attached",
   which is an instruction to the coin station that an Operator
   Services System has been connected. The GW sends the corresponding
   PSTN signaling back toward the coin station.

   In steps 8 through 10, the AS using the same procedures sends
   encapsulated ISUP with a SAP parameter with the FCI indicating "Coin
   Collect" which instructs the coin station to collect and report on
   coin deposits.

   The coin deposits will be signaled as tones over the trunk, so the
   AS in steps 11 through 14 subscribes to these events at the GW. This
   example assumes an extension to KPML to support these tones, but the
   mechanism is the same even if a new event package were defined.

   In 15, the user deposits coins into the station, and these events
   are signaled by the EO to the GW. In step 16, the GW sends SIP
   NOTIFY messages to the AS for each such event.

   When the AS determines that adequate payment has been collected, it
   routes the call, as depicted in steps 18 through 24.

   In this example, the caller exceeds his credit, and hangs up the
   phone. This is represented by steps 25 through 27.

   Using similar signaling, the OISP sends an Operator Hold and
   Ringback request toward the station, to "keep the line open" and to
   ring the station so that the user can be prompted to pay the
   exceeded credit. This is represented in steps 28 through 36. In this
   case, the honest user inserts the required coins, and this is
   signaled to the OISP in steps 39 through 41. From steps 42 on, the
   line is "released".















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            EO        GW        AS        MS   Called Party
             |         |         |         |         |
             |         |         |         |         |
             |         |         |         |         |
             |(1) Call Request Indication  |         |
             |-------->|         |         |         |
             |         |         |         |         |
             |         |(2) INVITE         |         |
             |         |-------->|         |         |
             |         |         |         |         |
             |         |(3) 200 OK         |         |
             |         |<--------|         |         |
             |         |         |         |         |
             |         |(4) ACK  |         |         |
             |         |-------->|         |         |
             |         |         |         |         |
             |         |(5) INFO (ISUP),SAP FCI=Network Service Attach)
             |         |<--------|         |         |
             |         |         |         |         |
             |         |(6) 200 OK         |         |
             |         |-------->|         |         |
             |         |         |         |         |
             |(7) corresponding MF or ISUP signaling |
             |<--------|         |         |         |
             |         |         |         |         |
             |         |(8) INFO (ISUP,SAP FCI=Coin Collect)
             |         |<--------|         |         |
             |         |         |         |         |
             |         |(9) 200 OK         |         |
             |         |-------->|         |         |
             |         |         |         |         |
             |(10) corresponding MF or ISUP signaling|
             |<--------|         |         |         |
             |         |         |         |         |
             |(11) SUBSCRIBE (KPML body specifying coin deposit tones)
             |<------------------|         |         |
             |         |         |         |         |
             |(12) 200 OK        |         |         |
             |------------------>|         |         |
             |         |         |         |         |
             |(13) NOTIFY (result of subscription)   |
             |------------------>|         |         |
             |         |         |         |         |
             |(14) 200 OK        |         |         |
             |<------------------|         |         |
             |         |         |         |         |
             |[ User inserts coins ]       |         |


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             |         |         |         |         |
             |         |         |         |         |
             |(15) Coin deposit signals    |         |
             |-------->|         |         |         |
             |         |         |         |         |
             |         |(16) NOTIFY (KPML body specifying coin deposit
   tones)
             |         |-------->|         |         |
             |         |         |         |         |
             |         |(17) 200 OK        |         |
             |         |<--------|         |         |
             |         |         |         |         |
             |[ AS determines adequate coinage, routes call ]
             |         |         |         |         |
             |         |         |         |         |
             |         |         |(18) INVITE        |
             |         |         |------------------>|
             |         |         |         |         |
             |         |         |(19) 180 Ringing   |
             |         |         |<------------------|
             |         |         |         |         |
             |         |         |(20) 200 OK        |
             |         |         |<------------------|
             |         |         |         |         |
             |         |         |(21) ACK |         |
             |         |         |------------------>|
             |         |         |         |         |
             |         |(22) re-INVITE (Called SDP)  |
             |         |<--------|         |         |
             |         |         |         |         |
             |         |(23) 200 OK        |         |
             |         |-------->|         |         |
             |         |         |         |         |
             |         |(24) RTP |         |         |
             |         |.............................|
             |         |         |         |         |
             |[ Conversation, exceeds credit ]       |
             |         |         |         |         |
             |         |         |         |         |
             |[ Caller hangs up, tries to run ]      |
             |         |         |         |         |
             |         |         |         |         |
             |(25) Disconnect Request      |         |
             |-------->|         |         |         |
             |         |         |         |         |
             |         |(26) INFO (ISUP,SAP FCI=Disconnect Request)
             |         |-------->|         |         |


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             |         |         |         |         |
             |         |(27) 200 OK        |         |
             |         |<--------|         |         |
             |         |         |         |         |
             |[ AS requests Connection Hold and Ringback ]
             |         |         |         |         |
             |         |         |         |         |
             |         |(28) INFO (ISUP,SAP FCI=Hold Request)
             |         |<--------|         |         |
             |         |         |         |         |
             |         |(29) 200 OK        |         |
             |         |-------->|         |         |
             |         |         |         |         |
             |(30) corresponding MF or ISUP signaling|
             |<--------|         |         |         |
             |         |         |         |         |
             |(31) Hold Acknowledge        |         |
             |-------->|         |         |         |
             |         |         |         |         |
             |         |(32) INFO (ISUP,SAP FCI=Hold Acknowledge)
             |         |-------->|         |         |
             |         |         |         |         |
             |         |(33) 200 OK        |         |
             |         |<--------|         |         |
             |         |         |         |         |
             |         |(34) INFO (ISUP,SAP FCI=Ringback Request)
             |         |<--------|         |         |
             |         |         |         |         |
             |         |(35) 200 OK        |         |
             |         |-------->|         |         |
             |         |         |         |         |
             |(36) corresponding MF or ISUP signaling|
             |<--------|         |         |         |
             |         |         |         |         |
             |[ User inserts coins ]       |         |
             |         |         |         |         |
             |         |         |         |         |
             |(37) NOTIFY (KPML body specifying coin deposit tones)
             |------------------>|         |         |
             |         |         |         |         |
             |(38) 200 OK        |         |         |
             |<------------------|         |         |
             |         |         |         |         |
             |[ Billing satisfied ]        |         |
             |         |         |         |         |
             |         |         |         |         |
             |         |(39) INFO (ISUP,SAP FCI=Hold Release Request)


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             |         |<--------|         |         |
             |         |         |         |         |
             |         |(40) 200 OK        |         |
             |         |-------->|         |         |
             |         |         |         |         |
             |(41) corresponding MF or ISUP signaling|
             |<--------|         |         |         |
             |         |         |         |         |
             |[ User hangs up ]  |         |         |
             |         |         |         |         |
             |         |         |         |         |
             |(42) Disconnect Request      |         |
             |-------->|         |         |         |
             |         |         |         |         |
             |         |(43) INFO (ISUP,SAP FCI=Disconnect Request)
             |         |-------->|         |         |
             |         |         |         |         |
             |         |(44) 200 OK        |         |
             |         |<--------|         |         |
             |         |         |         |         |
             |         |(45) BYE |         |         |
             |         |<--------|         |         |
             |         |         |         |         |
             |         |(46) 200 OK        |         |
             |         |-------->|         |         |
             |         |         |         |         |
             |(47) corresponding MF or ISUP signaling|
             |<--------|         |         |         |
             |         |         |         |         |
             |         |         |(48) BYE |         |
             |         |         |------------------>|
             |         |         |         |         |
             |         |         |(49) 200 OK        |
             |         |         |<------------------|
             |         |         |         |         |
             |         |         |         |         |
             |         |         |         |         |
                  Figure 19 Network Controlled Coin Call





11.2. Busy Line Verification and Interrupt

   An existing PTSN service is Busy Line Verification and Interrupt. In
   the Busy Line Verification (BLV) Service, a customer obtains


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   operator assistance to determine if a called line is in use. In
   Operator Interrupt Service, the operator provides a BLV Service and,
   if requested by the caller, interrupts a conversation in progress
   and relays a message. If the interrupted party is willing to hang
   up, the call can be reoriginated by the caller to the called party.
   At the caller's request, the connection between the caller and the
   called party can be reinitiated and handled by the operator as a
   Call Completion Service.

11.2.1. PSTN Target

   Currently, BLV/I is handled by the Operator Services System placing
   calls via special BLV/I trunk toward the target. Use of this type of
   trunk results in the Operator Services System being able to monitor
   a scrambled version of the target's conversation, and being able to
   barge in to speak to the target. In this document, the focus of
   BLV/I toward a PSTN target is on having the OIS components such as
   OWS and AS be able to communicate with the EO via BLV/I trunks. For
   IP targets, SIP capabilities are used.

   The following figure depicts a BLV/I call to a PSTN target. In steps
   (1) through (8) the caller is routed to an AS which performs 3PCC to
   connect this caller to an operator workstation.

   The operator determines the user's request, and initiates (9) a call
   toward the target via a BLV/I trunk. Ensuring that the call is
   routed via the correct type of trunk can be handled the same using
   SIP as in the PSTN; that is, by prepending specified routing digits
   to the target number. The operator is bridged by the EO onto the
   target's line, during which time no voice is sent toward the caller.
   A one way connection can be explicitly signaled, or the operator
   workstation can simply not send RTP at this time. The operator
   workstation or GW implements a scrambler so that only the presence
   or absence of speech can be determined, and the operator then
   reports to the caller on the status. If there is speech, then the
   operator reports that the line is busy, and may offer to interrupt
   the caller.

   If this is desired, the operator removes the scrambler, and
   indicates to the target of the caller's desire to call them, and
   drops off. The operator informs the caller of the result, and drops
   the caller, who may then re attempt the call. The option where the
   OISP offers the call as a call completion service is not shown here,
   but this poses no unique requirements with respect to call
   completion.




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          Caller      AS        WS        GW
             |[ Caller dials 0+ or 0- ]    |
             |(1) INVITE         |         |
             |-------->|         |         |
             |(2) 180 Ringing    |         |
             |<--------|         |         |
             |         |(3) INVITE         |
             |         |-------->|         |
             |         |(4) 200 OK         |
             |         |<--------|         |
             |         |(5) ACK  |         |
             |         |-------->|         |
             |(6) 200 OK         |         |
             |<--------|         |         |
             |(7) ACK  |         |         |
             |-------->|         |         |
             |(8) RTP  |         |         |
             |...................|         |
             |[ Caller is now connected to operator ]
             |         |         |(9) INVITE
             |         |         |-------->|
             |         |         |(10) 200 OK
             |         |         |<--------|
             |         |         |(11) ACK |
             |         |         |-------->|
             |         |         |(12) RTP |
             |         |         |.........|
             |[ Operator is now connected to BLV trunk ]
             |         |         |(13) BYE |
             |         |         |-------->|
             |         |         |(14) 200 OK
             |         |         |<--------|
             |[ Operator drops caller ]
             |(15) BYE |         |         |
             |<------------------|         |
             |(16) 200 OK        |         |
             |------------------>|         |
             |[ Caller may or may not place call, OISP uninvolved ]


                      Figure 20 BLV/I to PSTN Target







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11.2.2. SIP Target

   The following depicts a BLV/I call to a SIP target. Note that this
   is included mainly for completeness. The characteristics of POTS
   based subscribers support such a service, but many of those
   characteristics may not be applicable to SIP based endpoints. POTS
   access can carry only a single call at a time; as a packet switched
   technology SIP does not share this inherent restriction. There is
   typically a strong association between a physical POTS line and the
   address (phone number) used to reach it, while a SIP address of
   record is a logical address which can be registered with various
   endpoints, even simultaneously. Also, attempts towards such a set of
   devices can be tried in sequence or in parallel; thus the same
   concept of "busy" does not carry directly from POTS access to SIP.
   The ambiguity of "busy" may also have impacts on the "interrupt"
   aspect of this service.

   The approach detailed here is based on that described in the
   PacketCable Residential SIP Telephony Feature Specification, [RST].
   The main aspects of this approach include using the Event dialog
   package [RFC4235] to determine whether the device has an active
   call, and using the Join header in order to bridge onto the current
   conversation for monitoring and interrupting the user. Additional
   aspects include the operator workstation performing the scrambling
   function, and the use of a preconfigured network asserted
   workstation identity from which the user device must accept and
   process the BLV/I related requests.

   Steps 1 through 8 represent an incoming call to the OISP being
   connected to an operator workstation. The operator interacts with
   the caller and determines the BLV/I request.

   In steps 9 through 12, the operator workstation subscribes to the
   Dialog event package at the target party's UA, and receives a NOTIFY
   identifying any active dialogs.

   In 13 through 16, the workstation sends an INVITE with a Join header
   [RFC3911] to bridge onto the active call. The INVITE includes a P-
   Asserted-Identity value corresponding to the value prearranged
   between the OISP and the target's home provider. The user devices
   are configured to accept SUBSCRIBEs for Dialog event package and
   INVITEs with the Join header when the P-Asserted-Identity contains
   this value. Thus, the user device accepts the Join header.
   Initially, the workstation acts in a receive only mode, and further,
   implements an audio scrambler such that speech is distinguishable as
   such, but is non intelligible. Thus the operator can determine
   whether the person at the target device is in active conversation.


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   During this time, the workstation does not exchange media with the
   caller, who may be put on hold (not show here).

   The operator can then report the status to the caller, and offer the
   Interrupt service. If accepted, the scrambling function is removed
   from the voice path between operator and target, and the operator
   "barges in" on the conversation, informs the target party of the
   caller's request, and asks whether the target would like to accept
   the call. The operator can then drop the session with the target and
   inform the caller about the target's response. There is of course no
   guarantee of the target's or caller's subsequent actions.






































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          Caller      AS        WS      Target
             |[ Caller dials 0+ or 0- ]    |
             |(1) INVITE         |         |
             |-------->|         |         |
             |(2) 180 Ringing    |         |
             |<--------|         |         |
             |[ Simplified flow for brevity - straight to WS ]
             |         |(3) INVITE         |
             |         |-------->|         |
             |         |(4) 200 OK         |
             |         |<--------|         |
             |         |(5) ACK  |         |
             |         |-------->|         |
             |(6) 200 OK         |         |
             |<--------|         |         |
             |(7) ACK  |         |         |
             |-------->|         |         |
             |(8) RTP  |         |         |
             |...................|         |
             |[ Caller is now connected to operator ]
             |         |         |(9) SUBSCRIBE (Dialog)
             |         |         |-------->|
             |         |         |(10) 200 OK
             |         |         |<--------|
             |         |         |(11) NOTIFY (Dialog state)
             |         |         |<--------|
             |         |         |(12) 200 OK
             |         |         |-------->|
             |         |         |(13) INVITE (Join, dialog id)
             |         |         |-------->|
             |         |         |(14) 200 OK
             |         |         |<--------|
             |         |         |(15) ACK |
             |         |         |-------->|
             |         |         |(16) RTP |
             |         |         |.........|
             |         |         |(17) BYE |
             |         |         |-------->|
             |         |         |(18) 200 OK
             |         |         |<--------|
             |[ Operator informs caller of target's disposition ]
             |(19) BYE |         |         |
             |<------------------|         |
             |(20) 200 OK        |         |
             |------------------>|         |
                       Figure 21 BLV/I to SIP Target


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11.3. Inward Calls

   Typically, operator services are provided by the OISP serving a
   user's originating provider. In some cases, another OISP must be
   involved. One example is BLV/I, where an OISP can only invoke BLV/I
   for targets served by providers that the OISP serves. In the case of
   a caller desiring to invoke BLV/I to a target served by a different
   provider, the caller's request would be routed to the same OISP as
   usual. That OISP would identify the OISP serving the target, and
   initiate an "inward" call to an operator in that OISP, and request
   that operator to perform the BLV/I. For this feature, the initiating
   OISP acts as the caller to the OISP serving the target. Currently,
   Inward calls are originated by operators at operator workstations,
   and terminated to operators at operator workstations.

   Inward calls need to be distinguishable from calls from subscribers
   that are routed to operators. Further, inward calls should be
   accepted only from other OISPs, never from subscribers, and only
   from those OISPs with appropriate business relationships.

   The request should be screened based on the identity of originator.
   Since the From header can easily be spoofed, a network-asserted
   identity should be used for this. Within trust domains that use the
   P-Asserted-Identity [RFC3325] header as a network asserted identity,
   this header should be used for this purpose. Alternatively, the SIP
   Identity mechanism [RFC4474] can be used in domains where this is
   used for network asserted identity. Rather than maintain lists of
   every possible URI for which Inward requests are allowed, the
   decision could be based on the domain in the SIP URI. Requests from
   domains corresponding only to OISPs which are authorized to make
   Inward requests would be accepted.

   In the current North American PSTN, the digits dialed by the
   operator placing Inward call can be used to identify the type of
   service being requested, so that the destination OISP can properly
   handle the request. These digits are known as Operator Special
   Dialed Code (OSDC) digits. Thus, the Request-URI should include the
   OSDC digits, and the AS should populate the Request-URI as a SIP URI
   which includes the SIP domain of the destination OISP as well as the
   OSDC code.





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   For Inward calls to PSTN based OISPs, the call should be placed via
   a PSTN gateway, and should appear to the destination OISP the same
   as any other Inward call.



11.4. Intercept

   Intercept service provides the capability for a customer to be
   informed that a working number is no longer in service or why a
   working number is no longer in service. Basically, it provides
   announcements to the caller, which may be fixed or dynamic.
   Currently in the North American PSTN, Intercept may be handled by
   individual end offices, or may be sent to Operator Services Systems,
   which have specialized resources for handling such requests. When a
   call reaches a PSTN switch for a number which requires Intercept
   treatment, that switch, known as the "intercepted switch", initiates
   an Intercept request for that "intercepted number". The request to
   an OISP specifies the intercepted number, and an "intercept type",
   which provides an indication of the general reason for intercept.
   Often, the OISP needs to consult an "intercept database" to
   determine specific processing for a particular intercepted number.

   Currently, with MF, dedicated Intercept trunk groups are typically
   used, so the call is implicitly identified as such. The ANI digits
   identify the intercepted number, and the II digits identify the
   intercept type. For ISUP, dedicated trunk groups may or may not be
   used, but the SAP parameter identifies the intercept type, and the
   Called Party Number parameter identifies the intercepted number. In
   both cases, the key information conveyed include identification of
   the request as intercept, intercept type, and intercepted number.

11.4.1. Intercept Request Via SIP

   Intercept requests to a SIP based OISP need to convey the same
   information currently conveyed. Such requests can be treated as a
   call forwarded to an Intercept service. Thus, the Request-URI should
   identify the request as Intercept, as well as conveying the
   intercept type. The currently defined values for intercept type
   include regular, blank, and trouble. Prepending these with
   "intercept-" in the left hand side of the Request-URI unambiguously
   identifies the request as intercept and conveys the intercept type.
   Treating this as a redirection, the SIP History-Info header can be
   used to convey the intercepted number. An example of such an INVITE
   (relevant fields only) follows:




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   INVITE sip:intercept-trouble@oisp-c.example.com SIP/2.0
   From: <sip:7327581111@provider-a.example.com>;tag=1234567
   To: <sip:7327582222@provider-b.example.com>
   History-Info: <sip:7327582222@provider-b.example.com>; index=1
   Content-Type: application/sdp
   Content-Length: ...


   Upon receiving such a request, the AS would typically perform any
   required processing, including database lookups, and generate a
   request to a MS to play the specified announcement. The conventions
   described in [RFC4240] can be used for this.

   An example high level message flow follows:



































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     Intercepted domain    AS             MS
             |              |              |
             |              |              |
             |              |              |
   [ Receives a call requiring Intercept service ]
             |              |              |
             |              |              |
             |(1) INVITE ( r-URI->intercept type, Hist-
                           Info=intercepted number )
             |------------->|              |
             |              |              |
             |              |(2) INVITE (r-URI->RFC 4240 annc)
             |              |------------->|
             |              |              |
             |              |(3) 200 OK    |
             |              |<-------------|
             |              |              |
             |              |(4) ACK       |
             |              |------------->|
             |              |              |
             |(5) 183 Session Progress     |
             |<-------------|              |
             |              |              |
             |(6) RTP (announcements)      |
             |.............................|
             |              |              |
             |Caller hangs up              |
             |              |              |
             |              |              |
             |(7) BYE       |              |
             |------------->|              |
             |              |              |
             |(8) 200 OK    |              |
             |<-------------|              |
             |              |              |
             |              |(9) BYE       |
             |              |------------->|
             |              |              |
             |              |(10) 200 OK   |
             |              |<-------------|
             |              |              |
             |              |              |
                    Figure 22 Intercept Request Via SIP






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11.4.2. Intercept Request Via PSTN

   When intercept requests are received from PSTN interfaces, the PSTN
   gateway needs to translate the incoming signaling to SIP. The
   preferred approach is to have the PSTN gateway construct an INVITE
   request of the form described above for requests received via SIP.
   This method requires additional functionality on the part of the
   gateway, but the AS only needs to recognize one type of INVITE
   request for Intercept.

   Alternatively, the gateway could construct an INVITE containing
   encapsulated ISUP, in which the Called Party Number and SAP fields
   are most significant. Also, the Request-URI should contain the
   Called Party Number. With this method, the PSTN gateway treats the
   INVITE the same as other INVITEs, but requires the AS to recognize
   this as an Intercept request by examining the encapsulated ISUP body
   contents.
































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   Intercepted
    Switch         PSTN GW          AS             MS
      |              |              |              |
      |              |              |              |
      |              |              |              |
      |[ Receives a call requiring Intercept service ]
      |              |              |              |
      |              |              |              |
      |(1) IAM ( CdPN digits=intcptd number, CdPN NOA=op req,
                 SAP=intcpt type )
      |------------->|              |              |
      |              |              |              |
      |              |(2) INVITE (see above)
      |              |------------->|              |
      |              |              |              |
      |              |              |(3) INVITE (r-URI->RFC 4240 annc)
      |              |              |------------->|
      |              |              |              |
      |              |              |(4) 200 OK    |
      |              |              |<-------------|
      |              |              |              |
      |              |              |(5) ACK       |
      |              |              |------------->|
      |              |              |              |
      |              |(6) 183 Session Progress     |
      |              |<-------------|              |
      |              |              |              |
      |(7) ACM       |              |              |
      |<-------------|              |              |
      |              |              |              |
      |              |(8) RTP (announcements)      |
      |              |.............................|
      |              |              |              |
      |(9) TDM (announcements)      |              |
      |..............|              |              |
      |              |              |              |
      |Caller hangs up              |              |
      |              |              |              |
      |              |              |              |
      |(10) REL      |              |              |
      |------------->|              |              |
      |              |              |              |
      |              |(11) BYE      |              |
      |              |------------->|              |
      |              |              |              |
      |              |(12) 200 OK   |              |
      |              |<-------------|              |


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      |              |              |              |
      |(13) RLC      |              |              |
      |<-------------|              |              |
      |              |              |              |
      |              |              |(14) BYE      |
      |              |              |------------->|
      |              |              |              |
      |              |              |(15) 200 OK   |
      |              |              |<-------------|
      |              |              |              |
                   Figure 23 Intercept Request Via PSTN





11.5. Operator Assisted Collect Call

   The following call flow provides examples of how a specific operator
   service, Operator Assisted Collect Call, could be implemented using
   the mechanisms described in this document. The purpose is to
   illustrate one way to implement this service using the proposed
   signaling mechanisms. In practice, this particular service could be
   implemented in an automated fashion without human intervention.

























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   Caller     Proxy       AS        WS      Called      MS        ACD
      |         |         |         |         |         |         |
      |         |         |         |         |         |         |
      |         |         |         |         |         |         |
      |[ Caller dials 0+ or 0- ]    |         |         |         |
      |         |         |         |         |         |         |
      |         |         |         |         |         |         |
      |(1) INVITE         |         |         |         |         |
      |------------------>|         |         |         |         |
      |         |         |         |         |         |         |
      |(2) 100 Trying     |         |         |         |         |
      |<------------------|         |         |         |         |
      |         |         |         |         |         |         |
      |[ AS determines operator is needed, performs 3PCC ]        |
      |         |         |         |         |         |         |
      |         |         |         |         |         |         |
      |         |         |(3) INVITE         |         |         |
      |         |         |-------------------------------------->|
      |         |         |         |         |         |         |
      |         |         |(4) 3xx redirect to WS where selected
   operator registered
      |         |         |<--------------------------------------|
      |         |         |         |         |         |         |
      |         |         |(5) INVITE         |         |         |
      |         |         |-------->|         |         |         |
      |         |         |         |         |         |         |
      |         |         |(6) 200 OK         |         |         |
      |         |         |<--------|         |         |         |
      |         |         |         |         |         |         |
      |         |         |(7) ACK  |         |         |         |
      |         |         |-------->|         |         |         |
      |         |         |         |         |         |         |
      |(8) 200 OK         |         |         |         |         |
      |<------------------|         |         |         |         |
      |         |         |         |         |         |         |
      |(9) ACK  |         |         |         |         |         |
      |------------------>|         |         |         |         |
      |         |         |         |         |         |         |
      |[ Caller is now connected to operator ]|         |         |
      |         |         |         |         |         |         |
      |         |         |         |         |         |         |
      |(10) RTP |         |         |         |         |         |
      |.............................|         |         |         |
      |         |         |         |         |         |         |
      |[ Operator determines calling's request and places on hold]|
      |         |         |         |         |         |         |


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      |         |         |         |         |         |         |
      |         |         |(11) re-INVITE (HOLD)        |         |
      |         |         |<--------|         |         |         |
      |         |         |         |         |         |         |
      |         |         |(12) 200 OK        |         |         |
      |         |         |-------->|         |         |         |
      |         |         |         |         |         |         |
      |         |         |(13) ACK |         |         |         |
      |         |         |<--------|         |         |         |
      |         |         |         |         |         |         |
      |[ AS logic determines announcements should be played instead ]
      |         |         |         |         |         |         |
      |         |         |         |         |         |         |
      |         |         |(14) INVITE (play announcements)       |
      |         |         |---------------------------->|         |
      |         |         |         |         |         |         |
      |         |         |(15) 200 OK (SDP-MS)         |         |
      |         |         |<----------------------------|         |
      |         |         |         |         |         |         |
      |         |         |(16) ACK |         |         |         |
      |         |         |---------------------------->|         |
      |         |         |         |         |         |         |
      |(17) reINVITE (SDP-MS)       |         |         |         |
      |<------------------|         |         |         |         |
      |         |         |         |         |         |         |
      |(18) 200 OK (SDP-calling)    |         |         |         |
      |------------------>|         |         |         |         |
      |         |         |         |         |         |         |
      |(19) ACK |         |         |         |         |         |
      |<------------------|         |         |         |         |
      |         |         |         |         |         |         |
      |(20) RTP (MS plays announcements to calling)     |         |
      |.................................................|         |
      |         |         |         |         |         |         |
      |[ Operator calls called party ]        |         |         |
      |         |         |         |         |         |         |
      |         |         |         |         |         |         |
      |         |         |         |(21) INVITE        |         |
      |         |         |         |-------->|         |         |
      |         |         |         |         |         |         |
      |         |         |         |(22) 200 OK        |         |
      |         |         |         |<--------|         |         |
      |         |         |         |         |         |         |
      |         |         |         |(23) ACK |         |         |
      |         |         |         |-------->|         |         |
      |         |         |         |         |         |         |
      |         |         |         |(24) RTP |         |         |


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      |         |         |         |.........|         |         |
      |         |         |         |         |         |         |
      |[ Called agrees to accept charges ]    |         |         |
      |         |         |         |         |         |         |
      |         |         |         |         |         |         |
      |[ Operator takes Calling off hold ]    |         |         |
      |         |         |         |         |         |         |
      |         |         |         |         |         |         |
      |         |         |(25) re-INVITE (un-HOLD)     |         |
      |         |         |<--------|         |         |         |
      |         |         |         |         |         |         |
      |[ AS logic directs Calling from MS back to WS ]  |         |
      |         |         |         |         |         |         |
      |         |         |         |         |         |         |
      |(26) re-INVITE (SDP-ws)      |         |         |         |
      |<------------------|         |         |         |         |
      |         |         |         |         |         |         |
      |(27) 200 OK        |         |         |         |         |
      |------------------>|         |         |         |         |
      |         |         |         |         |         |         |
      |         |         |(28) 200 OK        |         |         |
      |         |         |-------->|         |         |         |
      |         |         |         |         |         |         |
      |         |         |(29) ACK |         |         |         |
      |         |         |<--------|         |         |         |
      |         |         |         |         |         |         |
      |(30) ACK |         |         |         |         |         |
      |<------------------|         |         |         |         |
      |         |         |         |         |         |         |
      |(31) RTP |         |         |         |         |         |
      |.............................|         |         |         |
      |         |         |         |         |         |         |
      |[ AS releases MS ] |         |         |         |         |
      |         |         |         |         |         |         |
      |         |         |         |         |         |         |
      |         |         |(32) BYE |         |         |         |
      |         |         |---------------------------->|         |
      |         |         |         |         |         |         |
      |         |         |(33) 200 OK        |         |         |
      |         |         |<----------------------------|         |
      |         |         |         |         |         |         |
      |[ Calling and Called both have RTP session with WS ]       |
      |         |         |         |         |         |         |
      |         |         |         |         |         |         |
      |[ WS bridges conversations together internally ] |         |
      |         |         |         |         |         |         |
      |         |         |         |         |         |         |


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      |[ After brief interlude WS transfers Calling directly to Called
   ]
      |         |         |         |         |         |         |
      |         |         |         |         |         |         |
      |[ then drops out ] |         |         |         |         |
      |         |         |         |         |         |         |
      |         |         |         |         |         |         |
      |         |         |(34) REFER (to called)       |         |
      |         |         |<--------|         |         |         |
      |         |         |         |         |         |         |
      |         |         |(35) 202 Accepted  |         |         |
      |         |         |-------->|         |         |         |
      |         |         |         |         |         |         |
      |         |         |(36) NOTIFY (trying)         |         |
      |         |         |-------->|         |         |         |
      |         |         |         |         |         |         |
      |         |         |(37) 200 OK        |         |         |
      |         |         |<--------|         |         |         |
      |         |         |         |         |         |         |
      |[ Replaces header causes Called to replace old call with new ]
      |         |         |         |         |         |         |
      |         |         |         |         |         |         |
      |         |         |(38) INVITE (replaces: WS )  |         |
      |         |         |------------------>|         |         |
      |         |         |         |         |         |         |
      |         |         |(39) 200 OK (SDP-called)     |         |
      |         |         |<------------------|         |         |
      |         |         |         |         |         |         |
      |         |         |(40) ACK |         |         |         |
      |         |         |------------------>|         |         |
      |         |         |         |         |         |         |
      |         |         |         |(41) BYE |         |         |
      |         |         |         |<--------|         |         |
      |         |         |         |         |         |         |
      |         |         |         |(42) 200 OK        |         |
      |         |         |         |-------->|         |         |
      |         |         |         |         |         |         |
      |[ The following interactions synch up SDP - optimization
   possible ]
      |         |         |         |         |         |         |
      |         |         |         |         |         |         |
      |(43) re-INVITE (SDP-called)  |         |         |         |
      |<------------------|         |         |         |         |
      |         |         |         |         |         |         |
      |(44) 200 OK (SDP-calling)    |         |         |         |
      |------------------>|         |         |         |         |
      |         |         |         |         |         |         |


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      |(45) ACK |         |         |         |         |         |
      |<------------------|         |         |         |         |
      |         |         |         |         |         |         |
      |         |         |(46) re-INVITE (SDP-calling) |         |
      |         |         |------------------>|         |         |
      |         |         |         |         |         |         |
      |         |         |(47) 200 OK        |         |         |
      |         |         |<------------------|         |         |
      |         |         |         |         |         |         |
      |         |         |(48) ACK |         |         |         |
      |         |         |------------------>|         |         |
      |         |         |         |         |         |         |
      |(49) RTP |         |         |         |         |         |
      |.......................................|         |         |
      |         |         |         |         |         |         |
      |[ Calling and Called are now talking directly ]  |         |
      |         |         |         |         |         |         |
      |         |         |         |         |         |         |
      |         |         |(50) NOTIFY (Call completed) |         |
      |         |         |-------->|         |         |         |
      |         |         |         |         |         |         |
      |         |         |(51) 200 OK        |         |         |
      |         |         |<--------|         |         |         |
      |         |         |         |         |         |         |
      |[ Operator now drops out ]   |         |         |         |
      |         |         |         |         |         |         |
      |         |         |         |         |         |         |
      |         |         |         |(52) BYE |         |         |
      |         |         |         |-------->|         |         |
      |         |         |         |         |         |         |
      |         |         |         |(53) 200 OK        |         |
      |         |         |         |<--------|         |         |
      |         |         |         |         |         |         |
      |[ AS remains in signaling path until call ends ] |         |
      |         |         |         |         |         |         |
      |         |         |         |         |         |         |
      |(54) BYE |         |         |         |         |         |
      |------------------>|         |         |         |         |
      |         |         |         |         |         |         |
      |         |         |(55) BYE |         |         |         |
      |         |         |------------------>|         |         |
      |         |         |         |         |         |         |
      |         |         |(56) 200 OK        |         |         |
      |         |         |<------------------|         |         |
      |         |         |         |         |         |         |
      |(57) 200 OK        |         |         |         |         |
      |<------------------|         |         |         |         |


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      |         |         |         |         |         |         |
      |         |         |         |         |         |         |
      |         |         |         |         |         |         |


                Figure 24   Operator Assisted Collect Call



   The caller initiates the call by dialing 0+ or 0-.

   The call is routed to the AS. The AS examines the calling party
   number and calling party's home provider, which are derived from the
   P-Asserted-Identity header. The charge number is also needed, in
   case the caller's service is determined by agreements with another
   party, such as the caller's employer. The employer may have a large
   number of calling identities representing its employees, which are
   covered under its agreement with the OISP. Rather than provision
   every possible calling number/identity with the OISP (and this may
   be constantly changing), the ability to pass a charge number would
   allow the OISP to determine whether this charge number has any
   associated treatment on a per charge number basis.

   In any case, in our example, the AS examines the request and
   determines that the call is for an operator assisted collect call.
   Typically a MS could be initially connected to prompt the user for
   the type of call. This step is omitted in this example.

   The AS performs third party call control (3PCC). It sends a 18x
   response towards the caller. It needs to initiate a call leg to an
   operator workstation. It populates the selection criteria in an
   INVITE message (the exact mechanism for this is under study) which
   it sends to the ACD server in (3). The ACD server identifies the
   best match available operator and returns the contact information
   for the workstation where that operator is currently registered in a
   3xx redirection response.

   In (5) the AS sets up a call to the workstation identified by the
   ACD server, and using 3PCC connects the caller to the WS, resulting
   in an RTP session in (10).

   The operator determines the caller's requested number, and sends an
   INVITE toward the AS to put the caller on hold. The logic in the AS
   determines that instead the caller should be connected to custom
   announcements, and in (14) through (20) creates a session between
   the caller and a MS.



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   Meanwhile, in (21) the WS places a call to the called party, and
   asks whether the called party would accept the charges for a collect
   call. In this example, the called party agrees to the request.

   In (25), the operator takes the caller off hold (recall that it
   believes it has placed the caller on hold). The AS, in (26) through
   (33), performs 3PCC, and removes the caller from the MS which is
   playing custom announcements, and reconnects the caller back to the
   WS. The WS uses its own internal bridging functionality to
   conference the operator, calling, and called parties.

   After a brief interlude, the operator initiates a transfer of the
   calling and called parties directly together using a REFER in (34)
   through (37). The AS, performing 3PCC, utilizes the SIP Replaces
   mechanism beginning in (38) to complete the transfer. When the
   transfer is complete, the operator drops out completely. Note that
   the AS, performing 3PCC, remains in the signaling path until the
   call is torn down in (54) through (57).



11.6. Operator Assisted Third Party Billing

   The Operator Assisted Third Party Billing service allows a caller to
   request billing of a call to a third party. In such a service, the
   caller calls the operator, who places a call to the billed party to
   obtain authorization for billing. If authorized, the OISP places the
   call to the called party, and bills it to the billed party. This
   document focuses on the call flow and SIP signaling, and does not
   discuss the billing mechanisms.

   In 1 through 8 below, the caller is connected to the operator. In 9
   through 14, the operator places the caller on hold, and in 15
   through 18 the operator calls the billed party to ask for
   authorization. In 21, the operator un-holds the caller and informs
   of the authorization. In 18 the operator initiates a call to the
   called party via the AS by sending a REFER to the AS.












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   Caller     CSCF       AS        WS      Billed    Called
      |         |         |         |         |         |
      |         |         |         |         |         |
      |         |         |         |         |         |
      |[ Caller dials 0+ or 0- ]    |         |         |
      |         |         |         |         |         |
      |         |         |         |         |         |
      |(1) INVITE         |         |         |         |
      |------------------>|         |         |         |
      |(2) 100 Trying     |         |         |         |
      |<------------------|         |         |         |
      |         |         |         |         |         |
      |[ AS determines operator is needed, performs 3PCC ]
      |         |         |         |         |         |
      |         |         |         |         |         |
      |         |         |(3) INVITE         |         |
      |         |         |-------->|         |         |
      |         |         |(4) 200 OK         |         |
      |         |         |<--------|         |         |
      |         |         |(5) ACK  |         |         |
      |         |         |-------->|         |         |
      |         |         |         |         |         |
      |(6) 200 OK         |         |         |         |
      |<------------------|         |         |         |
      |(7) ACK  |         |         |         |         |
      |------------------>|         |         |         |
      |         |         |         |         |         |
      |[ Caller is now connected to operator ]|         |
      |         |         |         |         |         |
      |         |         |         |         |         |
      |(8) RTP  |         |         |         |         |
      |.............................|         |         |
      |         |         |         |         |         |
      |[ Operator determines caller's request and places on hold]
      |         |         |         |         |         |
      |         |         |         |         |         |
      |         |         |(9) re-INVITE (HOLD)         |
      |         |         |<--------|         |         |
      |         |         |(10) 200 OK        |         |
      |         |         |-------->|         |         |
      |         |         |(11) ACK |         |         |
      |         |         |<--------|         |         |
      |         |         |         |         |         |
      |[ AS could optionally send caller to advertisements vs hold ]
      |         |         |         |         |         |
      |         |         |         |         |         |


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      |(12) re-INVITE (HOLD)        |         |         |
      |<------------------|         |         |         |
      |(13) 200 OK        |         |         |         |
      |------------------>|         |         |         |
      |(14) ACK |         |         |         |         |
      |<------------------|         |         |         |
      |         |         |         |         |         |
      |[ Operator calls billed party ]        |         |
      |         |         |         |         |         |
      |         |         |         |         |         |
      |         |         |         |(15) INVITE        |
      |         |         |         |-------->|         |
      |         |         |         |(16) 200 OK        |
      |         |         |         |<--------|         |
      |         |         |         |(17) ACK |         |
      |         |         |         |-------->|         |
      |         |         |         |         |         |
      |         |         |         |(18) RTP |         |
      |         |         |         |.........|         |
      |         |         |         |         |         |
      |[ Charges OK, operator disconnects billed party ]|
      |         |         |         |         |         |
      |         |         |         |         |         |
      |         |         |         |         |         |
      |         |         |         |(19) BYE |         |
      |         |         |         |-------->|         |
      |         |         |         |(20) 200 OK        |
      |         |         |         |<--------|         |
      |         |         |         |         |         |
      |[ Operator informs AS of result, un-HOLDs caller ]
      |         |         |         |         |         |
      |         |         |         |         |         |
      |         |         |(21) re-INVITE(result, un-HOLD)
      |         |         |<--------|         |         |
      |         |         |         |         |         |
      |(22) re-INVITE(un-HOLD)      |         |         |
      |<------------------|         |         |         |
      |(23) 200 OK        |         |         |         |
      |------------------>|         |         |         |
      |(24) ACK |         |         |         |         |
      |<------------------|         |         |         |
      |         |         |         |         |         |
      |         |         |(25) 200 OK        |         |
      |         |         |-------->|         |         |
      |         |         |(26) ACK |         |         |
      |         |         |<--------|         |         |
      |         |         |         |         |         |


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      |(27) RTP |         |         |         |         |
      |.............................|         |         |
      |         |         |         |         |         |
      |[ Operator informs caller, transfers AS to initiate call ]
      |         |         |         |         |         |
      |         |         |         |         |         |
      |         |         |(28) REFER         |         |
      |         |         |<--------|         |         |
      |         |         |(29) 202 Accepted  |         |
      |         |         |-------->|         |         |
      |         |         |         |         |         |
      |         |         |(30) NOTIFY (trying)         |
      |         |         |-------->|         |         |
      |         |         |(31) 200 OK        |         |
      |         |         |<--------|         |         |
      |         |         |         |         |         |
      |[ AS places call to called party, notifies WS on success ]
      |         |         |         |         |         |
      |         |         |         |         |         |
      |         |         |(32) INVITE        |         |
      |         |         |---------------------------->|
      |         |         |(33) 180 |         |         |
      |         |         |<----------------------------|
      |         |         |(34) 200 OK        |         |
      |         |         |<----------------------------|
      |         |         |(35) ACK |         |         |
      |         |         |---------------------------->|
      |         |         |         |         |         |
      |(36) re-INVITE     |         |         |         |
      |<------------------|         |         |         |
      |(37) 200 OK        |         |         |         |
      |------------------>|         |         |         |
      |(38) ACK |         |         |         |         |
      |<------------------|         |         |         |
      |         |         |         |         |         |
      |         |         |(39) NOTIFY (Call completed) |
      |         |         |-------->|         |         |
      |         |         |(40) 200 OK        |         |
      |         |         |<--------|         |         |
      |         |         |         |         |         |
      |[ Operator drops]  |         |         |         |
      |         |         |         |         |         |
      |         |         |         |         |         |
      |         |         |(41) BYE |         |         |
      |         |         |<--------|         |         |
      |         |         |(42) 200 OK        |         |
      |         |         |-------->|         |         |


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      |         |         |         |         |         |




            Figure 25 Operator Assisted Third Party Billed Call



12. Summary and Conclusions

The intent of this document is to explain how Directory Assistance and
Operator Services work, and explore how they could be implemented with
SIP. This includes both SIP originated requests as well as interworking
with requests from the PSTN.

A basic architecture utilizing an application server as the primary
controller, performing third party call control to route incoming calls
among media servers, operator workstations, etc. is described.
Interface to the PSTN is described using PSTN gateways which interwork
between ISUP or MF signaling and SIP.

Operator services in the North American PSTN often utilize MF trunks.
As there is currently no specific specification for MF/SIP
interworking, we assume that the PSTN gateway performs an internal MF
to ISUP translation.

The use of existing SIP mechanisms is described where possible. Some of
the main mechanisms described include third party call control, the
REFER method with several extensions (e.g. Replaces), the Join header,
Netann, and some of the ongoing work in the MEDIACTRL working group.

Several protocol gaps and issues were identified. These include:

Originating Line Information/ANI II Digits

Charge Number

Coin Deposit Tones

Carrier Information: ISUP TNS, CIP, and CSI parameters, and "cic",
"dai" tel URI parameters/

For conveyance of coin deposit tones, the document suggests that
extensions to KPML are one potential option, and shows how KPML could
be used to this end. Definition of an operator services SIP event
package is mentioned as another alternative.


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The desired next steps include soliciting feedback from the IETF
community on the choices and intended usages of the proposed
mechanisms.



13. Security Considerations

This document does not introduce any new security considerations. It
describes the use of protocol mechanisms which may have security
implications; the Security Considerations sections of the documents
defining these mechanisms should be consulted.



14. IANA Considerations

This revision of this document does not address IANA considerations. It
is not anticipated that this document will define any new protocol
extensions or other values requiring action of IANA.



15. Acknowledgements

The authors would like to thank Martin Dolly, Gary Munson, Spencer
Dawkins, and Cullen Jennings for their review, comments, and advice
with this document.





















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16. References



16.1. Normative References



   [RFC3261] Rosenberg, et al, J., "SIP: Session Initiation Protocol",
             RFC 3261, June 2002.

   [RFC4474] Peterson, Jennings, "Enhancements for Authenticated
             Identity Management in the Session Initiation Protocol
             (SIP)", RFC 4474, August 2006.

   [RFC3325]   Jennings, et al, "Private Extensions to the Session
             Initiation Protocol (SIP) for Asserted Identity within
             Trusted Networks", RFC 3325, November 2002.



16.2. Informative References



   [CSI]    Loreto, Terril, "Input 3rd-Generation Partnership Project
             (3GPP) Communications Service Identifiers Requirements on
             the Session Initiation Protocol (SIP)", draft-loreto-
             sipping-3gpp-ics-requirements-00.txt, June 2006. (work in
             progress)

   [RFC3324] Watson, "Short Term Requirements for Network Asserted
             Identity", RFC 3324, November 2004.

   [RFC3263] Rosenberg, Schulzrinne, "Session Initiation Protocol
             (SIP): Locating SIP Servers", RFC 3263, June 2002.

   [RFC4240] Burger, et al, "Basic Network Media Services with SIP",
             RFC 4240, December 2005.

   [RFC3725]   Rosenberg, et al, "Best Current Practices for Third
             Party Call Control (3pcc) in the Session Initiation
             Protocol (SIP)", RFC 3725, April 2004.






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   [IMS] 3GPP TS 23.228 V7.4.0 (2006-06) - 3rd Generation Partnership
             Project; Technical Specification Group Services and System
             Aspects; IP Multimedia Subsystem (IMS); Stage 2 (Release
             7)

   [NSS] American National Standards Institute, Inc., "ANSI Extensions
             to the Narrowband Signaling Syntax (NSS) - Syntax
             Definition", ATIS-1000008.2006, January 2006.

   [RFC4904] Gurbani, et al, "Representing Trunk Groups in tel/sip
             Uniform Resource Identifiers (URIs)", RFC 4904, June 2007.

   [RFC4730] Burger, Dolly, "A Session Initiation Protocol (SIP) Event
             Package for Key Press Stimulus (KPML)", RFC 4730, November
             2006.

   [RST]     PacketCable, " Residential SIP Telephony Feature
             Specification", PKT-SP-RSTF-I01-060927, September 2006.

   [RFC4235] Rosenberg, et al, "An INVITE-Initiated Dialog Event
             Package for the Session Initiation Protocol (SIP)", RFC
             4235, November 2005.

   [RFC3911] Mahy, et al, "The Session Initiation Protocol (SIP) "Join"
             Header", RFC 3911, October 2004.

   [RFC3398] Camarillo, et al, "Integrated Services Digital Network
             (ISDN) User Part (ISUP) to Session Initiation Protocol
             (SIP) Mapping", RFC 3398, December 2002.

   [RFC3840] Rosenberg, et al, "Indicating User Agent Capabilities in
             the Session Initiation Protocol (SIP)", RFC 3840, August
             2004.

   [RFC4483] Burger, et al, "A Mechanism for Content Indirection in
             Session Initiation Protocol (SIP) Messages", RFC 4483, May
             2006.

   [RFC2045] Freed, et al, "Multipurpose Internet Mail Extensions
             (MIME) Part One: Format of Internet Message Bodies", RFC
             2045, November 1996.

   [RFC3204] Zimmerer, et al, "MIME media types for ISUP and QSIG
             Objects", RFC 3204, November 2001.





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   [RFC3325] Jennings, et al, "Private Extensions to the Session
             Initiation Protocol (SIP) for Asserted Identity within
             Trusted Networks", RFC 3325, November 2002.

   [RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers", RFC
             3966, December 2004.

   [RFC4244] Barnes, et al, "An Extension to the Session Initiation
             Protocol (SIP) for Request History Information", RFC 4244,
             November 2005.

   [RFC4694] Yu, J., "Number Portability Parameters for the "tel" URI",
             RFC 4694, October 2006.

   [RFC5552] Burke, D. and Scott, M., "SIP Interface to VoiceXML Media
             Services", RFC 5552, May 2009.

   [DAI] Yu, et al, "DAI Parameter for the tel URI", draft-yu-tel-dai-
             07, July 2009. (work in progress)

   [T1679] Alliance for Telecommunications Industry Solutions (ATIS)
             Committee T1, "American National Standard for
             Telecommunications - Interworking between Session
             Initiation Protocol (SIP) and Bearer Independent Call
             Control or ISDN User Part", ATIS T1.679-2004, June 2004.

   [PCI] York, et al, "P-Charge-Info: A Private Header (P-Header)
             Extension to the Session Initiation Protocol (SIP)",
             draft-york-sipping-p-charge-info-07, August 2009. (work in
             progress)

   [RFC3323] Peterson, J., "A Privacy Mechanism for the Session
             Initiation Protocol (SIP)", RFC 3323, November 2002.

   [draft-mahy-iptel-cpc] Mahy, R., "The Calling Party's Category tel
             URI Parameter (SIP)", draft-mahy-iptel-cpc-06.txt, March
             2007.

   [RFC3891] Mahy, R. et al., "The Session Initiation Protocol (SIP)
             "Replaces" Header", RFC 3891, September 2004.

   [RFC5079] Rosenberg, J., "Rejecting Anonymous Requests in the
             Session Initiation Protocol (SIP)", RFC 5079, December
             2007.





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Author's Addresses

      John Haluska
      Telcordia Technologies, Inc.
      331 Newman Springs Road
      Room 2Z-323
      Red Bank, NJ  07701-5699
      USA

      Phone: +1 732 758 5735
      Email: jhaluska@telcordia.com


      Renee Berkowitz
      Telcordia Technologies, Inc.
      One Telcordia Drive
      Piscataway, NJ  08854-4157
      USA

      Phone: +1 732 699 4784
      Email: rberkowi@telcordia.com


      Paul Roder
      Telcordia Technologies, Inc.
      One Telcordia Drive
      Room RRC-4A619
      Piscataway, NJ  08854-4157
      USA

      Phone: +1 732 699 6191
      Email: proder2@telcordia.com

      Wesley Downum
      Telcordia Technologies, Inc.
      One Telcordia Drive
      Piscataway, NJ  08854-4157
      USA

      Phone: +1 732 699 6201
      Email: wdownum@telcordia.com


      Richard Ahern
      AT&T Customer Information Services
      1876 Data Drive
      Room 314


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      Hoover, AL  35244
      USA

      Email: Richard.Ahern@bellsouth.com


      Paul Lum Lung
      Qwest Communications International
      1801 California Street
      Suite 1210
      Denver, CO  80202
      USA

      Email: paul.lumlung@qwest.com


     Nicholas S. Costantino
     Soleo Communications, Inc.
     300 Willowbrook Drive
     Fairport, NY 14450

     Email: ncostantino@soleocommunications.com


     Chris Blackwell
     Verizon
     1000 Century Tel Dr
     Room 115
     Wentzville, MO 63385

     Email: chris.blackwell@verizon.com



     D. E. Scott
     VoltDelta
     2401 N. Glassell St.
     Orange, CA  92865-2705

     Email: dscott@voltdelta.com









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