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<rfc category="bcp" ipr="trust200902">
  <front>
    <title abbrev="Emergency Call Phone BCP">Best Current Practice for
    Communications Services in support of Emergency Calling</title>

    <author fullname="Brian Rosen" initials="B.R" surname="Rosen">
      <organization>NeuStar</organization>

      <address>
        <postal>
          <street>470 Conrad Dr.</street>

          <city>Mars</city>

          <region>PA</region>

          <code>16046</code>

          <country>USA</country>
        </postal>

        <phone>+1 724 382 1051</phone>

        <email>br@brianrosen.net</email>
      </address>
    </author>

    <author fullname="James Polk" initials="J.P." surname="Polk">
      <organization>Cisco Systems</organization>

      <address>
        <postal>
          <street>3913 Treemont Circle</street>

          <city>Colleyville</city>

          <region>TX</region>

          <code>76034</code>

          <country>USA</country>
        </postal>

        <phone>+1-817-271-3552</phone>

        <email>jmpolk@cisco.com</email>
      </address>
    </author>

    <date year="2011" />

    <area>rai</area>

    <workgroup>ecrit</workgroup>
<abstract>
<t>The IETF and other standards organization have efforts targeted at standardizing various aspects of placing emergency 
calls on IP networks. This memo describes best current practice on how devices, networks and services using IETF protocols should use 
such standards to make emergency calls.</t>
</abstract></front><middle>
<section title="Terminology">
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", 
"RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in <xref 
target="RFC2119"></xref>.</t>
<t>This document uses terms from <xref target="RFC3261"></xref>, <xref target="RFC5012"></xref> and 
<xref target="I-D.ietf-ecrit-framework"></xref>.</t>
</section><section title="Introduction">
<t>This document describes how access networks, Session Initiation Protocol <xref target="RFC3261"/> user agents, proxy servers and Public Safety Access Points (PSAPs) support emergency calling, as 
outlined in <xref target="I-D.ietf-ecrit-framework"></xref>, which is designed to complement the 
present document in section headings, numbering and content. Understanding <xref target="I-D.ietf-ecrit-framework"></xref> is necessary to understand this document.  This BCP succinctly describes the 
requirements of end devices and applications (requirements prefaced by "ED-"), access networks (including enterprise access networks)
(requirements prefaced by "AN-"), service providers (requirements prefaced by "SP-") and PSAPs to 
achieve globally interoperable emergency calling on the Internet. </t>
<t>This document also defines requirements for "Intermediate" devices
which exist between end devices or applications and the access network.  For example, a home router is
an "Intermediate" device.  Reporting location on an emergency call (see <xref target="Location"></xref>) 
may depend on the ability of such intermediate devices to meet the requirements prefaced by "INT-".</t>
<t>The access network requirements apply to those networks which may be used to place emergency calls using IETF protocols.  Local regulations may impact the need to support this document's access network requirements.</t>
<t>Other organizations, such as the North American Emergency Number Association (NENA), define the PSAP interface.  NENA's documents reference this document.</t>
</section><section title="Overview of how emergency calls are placed">
<t>An emergency call can be distinguished (<xref target="Identifying"></xref>) from any other call 
by a unique Service URN <xref target="RFC5031"></xref>, which is placed in the 
call set-up signaling when a home or visited emergency dial string is detected. Because emergency 
services are local to specific geographic regions, a caller must obtain his location (<xref 
target="Location"></xref>) prior to making emergency calls. To get this location, either a form of 
measuring (e.g., GPS) (<xref target="EndSystemMeasuredLocation"></xref>) device location in 
the endpoint is deployed, or the endpoint is configured (<xref 
target="LocationConfiguration"></xref>) with its location from the access network's Location
Information Server (LIS). The location is conveyed (<xref target="Conveyance"></xref>) in the SIP 
signaling with the call. The call is routed (<xref target="Routing"></xref>) based on location 
using the Location-to-Service Translation (LoST) protocol <xref target="RFC5222"></xref>, which maps a location to 
a set of PSAP URIs. Each URI 
resolves to a PSAP or an Emergency Services Routing Proxy (ESRP), which serves a group of PSAPs. The 
call arrives at the PSAP with the location included in the SIP INVITE request. </t>
</section><section anchor="WhichDevices" title="Which devices and services should support emergency calls">
<t>ED-1 A device or application that implements SIP calling SHOULD
   support emergency calling. Some jurisdictions have regulations
   governing which devices need to support emergency calling and
   developers are encouraged to ensure that devices they develop
   meet relevant regulatory requirements. Unfortunately, the
   natural variation in those regulations also makes it impossible
   to accurately describe the cases when developers do or do not have
   to support emergency calling.</t>
<t>SP-1 If a device or application expects to be able to place a call for help, the service provider that 
supports it MUST facilitate emergency calling.  Some jurisdictions have regulations governing
this.</t>
<t>ED-2 Devices that create media sessions and exchange real-time audio, video and/or text, have the 
capability to establish sessions to a wide variety of addresses, and communicate over private IP 
networks or the Internet, SHOULD support emergency calls.  Some jurisdictions have regulations governing
this.</t>
</section><section anchor="Identifying" title="Identifying an emergency call">
<t>ED-3 Endpoints SHOULD recognize dial strings of emergency calls.  If the service provider
always knows the location of the device (the correct dial string depends on which country you are in), the service provider may recognize them, see SP-2.</t>
<t>SP-2 Proxy servers SHOULD recognize emergency dial strings if for some 
reason the endpoint does not recognize them. </t>
<t>ED-4/SP-3 Emergency calls MUST be marked with a Service URN in the Request-URI of the 
INVITE.</t>
<t>ED-5/SP-4 Geographically local dial strings MUST be recognized.</t>
<t>ED-6/SP-5 Devices MUST be able to be configured with the home country from which the home dial string(s)
can be determined.</t>
<t>ED-7/SP-6 Emergency dial strings SHOULD be determined from LoST 
<xref target="RFC5222"></xref>.  Dial Strings MAY be configured directly into the device.</t>
<t>AN-1 LoST servers MUST return dial strings for emergency services.</t>
<t>ED-8 Endpoints which do not recognize emergency dial strings SHOULD send dial strings as per 
<xref target="RFC4967"></xref>.</t>
<t>SP-7 If a proxy server recognizes dial strings on behalf of its clients, it MUST recognize emergency dial strings represented by <xref 
target="RFC4967"></xref> and SHOULD recognize the emergency dial strings represented by a tel URI <xref 
target="RFC3966"></xref>.</t>
<t>ED-9 Endpoints SHOULD be able to have home dial strings provisioned.</t>
<t>SP-8 Service providers MAY provision home dial strings in devices.</t>
<t>ED-10 Devices SHOULD NOT have one button emergency calling initiation.</t>
<t>ED-11/SP-9 All sub-services for the 'sos' service specified in <xref target="RFC5031"></xref>. 
MUST be recognized.</t> 
</section><section anchor="Location" title="Location and its role in an emergency call">
<t>Handling location for emergency calling usually involves several steps to process and multiple entities are involved. In 
Internet emergency calling, where the endpoint is located is "determined" using a variety of 
measurement or wiretracing methods. Endpoints can be "configured" with their own location by the 
access network. In some circumstances, a proxy server can insert location into the signaling on 
behalf of the endpoint. The location is "mapped" to the URI to send the call to, and the location 
is "conveyed" to the PSAP (and other entities) in the signaling. Likewise, we employ Location 
Configuration Protocols (LCPs), the Location-to-Service Mapping Protocol, and Location Conveyance Protocols for these 
functions. The Location-to-Service Translation protocol 
<xref target="RFC5222"></xref> is the Location Mapping Protocol defined by the 
IETF.</t>
<section anchor="LocationTypes" title="Types of location information">
<t>There are several forms of location. All IETF location configuration and location conveyance protocols support both civic and geospatial (geo) 
forms. The civic forms include both postal and jurisdictional fields. A cell 
tower/sector can be represented as a point (geo or civic) or polygon. 
Endpoints, Intermediate Devices and Service  Providers receiving 
  other forms of location representation MUST map them into either 
  a geo or civic for use in emergency calls.
</t>
<t>ED-12/INT-1/SP-10 Endpoints, Intermediate Devices and Service Providers MUST be prepared to handle 
location represented in either civic or geo form.</t>
<t>ED-13/INT-2/SP-11/AN-2 Entities MUST NOT convert (civic to geo or geo to civic) from the form of 
location the determination mechanism (see Section <xref target="LocationDetermination"/>) supplied prior to receipt by the PSAP.</t>
</section><section anchor="LocationDetermination" title="Location Determination">
<t>ED-14/INT-3/AN-3 Any location determination mechanism MAY be used, provided the accuracy of the location meets local requirements.</t>
<section anchor="UserLocation" title="User-entered location information">
<t>ED-15/INT-4/AN-4 Devices, intermediate Devices and/or access networks SHOULD support a manual method to override the 
location the access network determines. When the override location is supplied in civic form, it MUST be possible for the resultant Presence Information Data Format - Location Object (PIDF-LO) received at the PSAP to contain any of the elements specified in <xref target="RFC4119"></xref> and <xref target="RFC5139"></xref>.</t>
</section><section anchor="WireDatabase" title='Access network "wire database" location
information'>
<t>AN-5 Access networks supporting copper, fiber or other hard wired IP packet service SHOULD 
support location configuration. If the network does not support location configuration, it MUST 
require every device or intermediate device that connects to the network to support end system measured location.</t>
<t>AN-6/INT-5 Access networks and intermediate devices providing wire database location information SHOULD provide interior 
location data (building, floor, room, cubicle) where possible. It is RECOMMENDED that interior location be provided when spaces 
exceed approximately 650 square meters.  See <xref target="I-D.ietf-ecrit-framework"/> Section 6.2.2 for a discussion of how this value was determined.</t>
<t>AN-7/INT-6 Access networks and intermediate devices (including enterprise networks) which support intermediate range wireless 
connections (typically 100m or less of range) and which do not support a more accurate location 
determination mechanism such as triangulation, MUST support location configuration where
the location of the access point is reflected as the location of the clients of that access point. </t> 
<t>AN-8/INT-7 Where the
access network provides location configuration, intermediate devices MUST either be transparent to it,
or provide an interconnected client for the supported configuration mechanism and a server for a
configuration protocol supported by end devices downstream of the intermediate device such that the location provided by the access network is available to clients as if the intermediate device was not in the path.</t>
</section><section anchor="EndSystemMeasuredLocation" title="End-system measured location information">
<t>ED-16/INT-8 Devices MAY support end-system measured location. See <xref target="I-D.ietf-ecrit-framework"/> Section 6 for a discussion of accuracy of location.</t>
<t>ED-17/INT-9/AN-9 Devices that support endpoint measuring of location MUST have at least a coarse 
location capability (typically &lt;1km accuracy) for routing of calls. 
The location mechanism MAY be a service provided by the access network.</t>
</section><section anchor="NetworkMeasuredLocation" title="Network-measured location information">
<t>AN-10 Access networks MAY provide network-measured location determination. Wireless access 
networks that do not supply network measured location MUST require every device or intermediate device connected to the 
network to support end-system measured location. Uncertainty and confidence may be specified by local regulation.  Where not specified, uncertainty of less than 100 meters with 95% confidence is RECOMMENDED for dispatch location.</t>
<t>AN-11 Access networks that provide network measured location MUST have at least a coarse location 
(typically &lt;1km when not location hiding) capability at all times for routing of calls.</t>
<t>AN-12 Access networks with range of &lt;10 meters (e.g. personal area networks such as Bluetooth 
MUST provide a location to mobile devices connected 
to them. The location provided SHOULD be that reported by the upstream access network unless a more accurate mechanism 
is available.</t>
</section></section><section anchor="WhoAddsLocation" title="Who adds location, endpoint or proxy">
<t>ED-18/INT-10 Endpoints SHOULD attempt to configure their own location using the Location Configuration Protocols (LCPs) listed in ED-21.</t>
<t>SP-12 Proxies MAY provide location on behalf of devices if:
<list style="symbols">
<t>The proxy has a relationship with all access networks the device could connect to, and the 
relationship allows it to obtain location.</t>
<t>The proxy has an identifier, such as an IP address, that can be used by the access network to determine the location of the 
endpoint, even in the presence of NAT and VPN tunnels that may obscure the identifier between the access 
network and the service provider.</t>
</list></t>
<t>ED-19/INT-11/SP-13 Where proxies provide location on behalf of endpoints, the service provider MUST 
ensure that either the end device is provided with the local dial strings for its current location 
(where the end device recognizes dial strings), or the service provider proxy MUST detect the appropriate 
local dial strings at the time of the call.</t>
</section><section anchor="LocationReference" title="Location and references to location">
<t>ED-20/INT-12 Devices SHOULD be able to accept and forward location by value or by reference. An end 
device that receives location by reference (and does not also get the corresponding value) MUST be 
able to perform a dereference operation to obtain a value.</t>
</section><section anchor="LocationConfiguration" title="End system location configuration">
<t>Obtaining location from the access network may be preferable even if the device can measure its own location, especially indoors where most measurement mechanisms are not accurate enough.  This sections requirements do not apply to devices that can accurately measure their own location.</t>
<t>ED-21/INT-13 Devices MUST support both the Dynamic Host Configuration Protocol (DHCP) location options <xref target="RFC4776"></xref>, 
<xref target="RFC6225"></xref> and HTTP Enabled Location Delivery (HELD) <xref target="RFC5985"></xref>.
When devices deploy a specific access network interface for which location 
configuration mechanisms such as Link Layer Discovery Protocol - Media Endpoint Discovery (LLDP-MED) <xref target="LLDP-MED"/> or 802.11v are specified, the device SHOULD support the additional respective access network 
specific location configuration mechanism.</t>
<t>AN-13/INT-14 The access network MUST support either DHCP location
   options or HELD.  The access network SHOULD support other location
   configuration technologies that are specific to the type of access
   network.</t>
<t>AN-14/INT-15 Where a router is employed between a LAN and WAN in a small (less than approximately 
650 square meters) area, the router MUST be transparent to the location provided by the WAN to the LAN.  This may
mean the router must obtain location as a client from the WAN, and supply an LCP server to the LAN with
the location it obtains.  Where the area is larger, the LAN MUST have a location configuration mechanism 
satisfying the requirements of this document.</t>
<t>ED-22/INT-16 Endpoints SHOULD try all LCPs supported by the device in any order or in parallel. The 
first one that succeeds in supplying location MUST be used.</t>
<t>AN-15/INT-17 Access networks that support more than one LCP MUST reply with the same location
information (within the limits of the data format for the specific LCP) for all LCPs it 
supports.</t>
<t>ED-23/INT-18/SP-14 When HELD is the LCP, the request MUST specify a value of "emergencyRouting" for 
the "responseTime" parameter and use the resulting location for routing.  If a value for dispatch location 
will be sent, another request with the "responseTime" parameter set to "emergencyDispatch" must be 
completed, with the result sent for dispatch purposes.</t>
<t>ED-24  Where the operating system supporting application programs which need location for emergency calls
does not allow access to Layer 2 and Layer 3 functions necessary for a client application to use DHCP location
options and/or other location technologies that are specific to the type of 
access network, the operating system MUST provide a published API conforming to ED-12 through 
ED-23 and ED-25 through ED-32.  It is RECOMMENDED that all operating systems provide such an API.</t> 
</section><section anchor="WhenConfigure" title="When location should be configured">
<t>If an endpoint is manually configured, the requirements in this section are not applicable.</t>
<t>ED-25/INT-19 Endpoints SHOULD obtain location immediately after obtaining local network configuration 
information.</t>
<t>ED-26/INT-20 If the device is configured to use DHCP for bootstrapping, and does not use it MUST include both options 
for location acquisition (civic and geodetic), the option for LIS discovery, and the option for LoST discovery 
as defined in <xref target="RFC4776"></xref>, <xref target="RFC6225"></xref>,
<xref target="RFC5986"></xref> and 
<xref target="RFC5223"></xref>.</t> 
<t>ED-27/INT-21 If the device sends a DHCPINFORM message, it MUST include both options 
for location acquisition (civic and geodetic), the option for LIS discovery, and the option for LoST discovery 
as defined in <xref target="RFC4776"></xref>, <xref target="RFC6225"></xref>, 
<xref target="RFC5986"></xref> and 
<xref target="RFC5223"></xref>.</t> 
<t>ED-28/INT-22 To minimize the effects of VPNs that do not allow packets to be sent via the native hardware interface
rather than via the VPN tunnel, location configuration SHOULD be attempted 
before such tunnels are established.</t>
<t>ED-29/INT-23 Software which uses LCPs SHOULD locate and use the actual hardware network interface rather
than a VPN tunnel interface to direct LCP requests to the LIS in the actual access network.</t>
<t>AN-16 Network administrators MUST take care in assigning IP addresses such that VPN address 
assignments can be distinguished from local devices (by subnet choice, for example), and LISs 
SHOULD NOT attempt to provide location to addresses that arrive via VPN connections unless it can
accurately determine the location for such addresses. </t>
<t>AN-17 Placement of NAT devices where an LCP uses IP address for an identifier SHOULD 
consider the effect of the NAT on the LCP. The address used to query the LIS MUST be able to correctly
identify the record in the LIS representing the location of the querying device</t>
<t>ED-30/INT-24 For devices which are not expected to change location, refreshing location on the order of once per day is 
RECOMMENDED.</t>
<t>ED-31/INT-25 For devices which roam, refresh of location information SHOULD be more frequent, with the frequency 
related to the mobility of the device and the ability of the access network to support the refresh 
operation. If the device detects a link state change that might indicate having moved, for example when it 
changes access points, the device SHOULD refresh its location.</t>
<t>ED-32/INT-26/AN-18 It is RECOMMENDED that location determination not take longer than 250 ms to obtain 
routing location and systems SHOULD be designed such that the typical response is under 100 ms. 
However, as much as 3 seconds to obtain routing location MAY be tolerated if location accuracy can 
be substantially improved over what can be obtained in 250 ms.</t>
</section><section anchor="Conveyance" title="Conveying location">
<t>ED-33/SP-15 Location sent between SIP entities MUST be conveyed using 
<xref target="I-D.ietf-sipcore-location-conveyance"></xref>.</t>
</section><section anchor="LocationUpdate" title="Location updates">
<t>ED-34/AN-19 Where the absolute location or the accuracy of location of the endpoint may change 
between the time the call is received at the PSAP and the time dispatch is completed, location 
update mechanisms MUST be implemented and used.</t>
<t>ED-35/AN-20 Mobile devices MUST be provided with a mechanism to get repeated location updates to 
track the motion of the device during the complete processing of the call.</t>
<t>ED-36/AN-21 The LIS SHOULD provide a location reference which permits a subscription with 
appropriate filtering.</t>
<t>ED-37/AN-22 For calls sent with location-by-reference, with a SIP or SIPS scheme, the server 
resolving the reference MUST support a SUBSCRIBE <xref target="RFC3265"></xref> to the presence 
event <xref target="RFC3856"></xref>. For other location-by-reference schemes that do not support subscription, the PSAP will have to
repeatedly dereference the URI to determine if the device moved. </t>
<t>ED-38 If location was sent by value, and the endpoint gets updated location, it MUST send the 
updated location to the PSAP via a SIP re-INVITE or UPDATE request. Such updates SHOULD be limited to no more than 
one update every 10 seconds, a value selected to keep the load on a large PSAP manageable, and yet provide sufficient indication to the PSAP of motion.</t>
</section><section anchor="MultipleLocations" title="Multiple locations">
<t>ED-39/SP-16 If the LIS has more than one location for an endpoint it MUST conform to the rules in Section 3 of 
<xref target="RFC5491"></xref></t>
<t>ED-40 If an endpoint has more than one location available to it, it MUST choose one location to 
route the call towards the PSAP.  If multiple locations are in a single Presence Information Data Format (PIDF), the procedures in
<xref target="RFC5491"></xref> MUST be followed.  If the endpoint has
multiple PIDFs, and has no reasonable basis to choose from among them, a random choice is acceptable.</t>
<t>SP-17 If a proxy inserts location on behalf of an endpoint, and it has multiple locations 
available for the endpoint it MUST choose one location to use to route the call towards the PSAP. 
If multiple locations are in a single PIDF, the procedures in
<xref target="RFC5491"></xref> MUST be followed.  If the proxy has
multiple PIDFs, and has no reasonable basis to choose from among them, a random choice is acceptable.</t>
<t>SP-18 If a proxy is attempting to insert location but the endpoint conveyed a location to it, the 
proxy MUST use the endpoint's location for routing in the initial INVITE and MUST convey that location towards the PSAP. It MAY 
also include what it believes the location to be in a separate Geolocation header.</t>
<t>SP-19 All location objects received by a proxy MUST be delivered to the PSAP.</t>
<t>ED-41/SP-20 Location objects MUST be created with information about the method by which the location was 
determined, such as GPS, manually entered, or based on access network topology included in a PIDF-
LO "method" element. In addition, the source of the location information MUST be included in a 
PIDF-LO "provided-by" element.</t>
<t>ED-42/SP-21 A location with a method of "derived" MUST NOT be used unless no other location is
available.</t>
</section><section anchor="Validation" title="Location validation">
<t>AN-23 A LIS SHOULD perform location validation of civic locations via LoST before 
entering a location in its database.</t>
<t>ED-44 Endpoints SHOULD validate civic locations when they receive them from their LCP. 
Validation SHOULD be performed in conjunction with the LoST route query to minimize load on the 
LoST server.</t>
</section><section anchor="DefaultLocation" title="Default location">
<t>AN-24 When the access network cannot determine the actual location of the caller, it MUST supply 
a default location. The default SHOULD be chosen to be as close to the probable location of the 
device as the network can determine.  See <xref target="I-D.ietf-ecrit-framework"></xref></t>
<t>SP-22 Proxies handling emergency calls MUST insert a default location in the INVITE if the incoming INVITE does not 
contain a location and the proxy does not have a method for obtaining a better location.</t>
<t>AN-25/SP-23 Default locations MUST be marked with method=Default and the proxy MUST be identified
in provided-by element of the PIDF-LO.</t>
</section><section anchor="OtherLocation" title="Other location considerations">
<t>ED-45 If the LCP does not return location in the form of a PIDF-LO <xref 
target="RFC4119"></xref>, the endpoint MUST map the location information it receives from the 
configuration protocol to a PIDF-LO.</t>
<t>ED-46/AN-26 To prevent against spoofing of the DHCP server, entities implementing DHCP for 
location configuration SHOULD use <xref target="RFC3118"></xref>, although the difficulty in providing
appropriate credentials is significant.</t>
<t>ED-47 If S/MIME <xref target="RFC5751"/> is used, the INVITE message MUST provide enough information unencrypted for intermediate proxies to route the call based on the location information included.  This would include the Geolocation header, and any bodies containing location information.  Use of S/MIME with emergency calls is NOT RECOMMENDED for this reason.</t>
<t>ED-48/SP-24 TLS
<xref target="RFC5746"></xref> MUST be used to protect location (but see <xref target="TLS"></xref>).  All implementations MUST support TLS. </t>
</section>
</section><section title="LIS and LoST Discovery">
<t>ED-49  Endpoints MUST support one or more mechanisms that allow them to determine 
their public IP address, for example, STUN <xref target="RFC5389"></xref>.</t>
<t>ED-50  Endpoints MUST support LIS discovery as described in <xref target="RFC5986"></xref>, and 
the LoST discovery as described in <xref target="RFC5223"></xref>. </t>
<t>ED-51  The device MUST have a configurable default LoST server parameter. 
</t>
<t>ED-52 DHCP LoST discovery MUST be used, if available, in preference to configured LoST servers.
That is, the endpoint MUST send queries to this LoST server first, using 
other LoST servers only if these queries fail.</t>
<t>AN-27 Access networks which support DHCP MUST implement the LIS and LoST discovery options in their DHCP servers and return suitable server addresses as appropriate.</t>

</section><section anchor="Routing" title="Routing the call to the PSAP">
<t>ED-53 Endpoints who obtain their own location SHOULD perform LoST mapping to the PSAP URI.</t>
<t>ED-54 Mapping SHOULD be performed at boot time and whenever location changes beyond the service 
boundary obtained from a prior LoST mapping operation or the time-to-live value of that response 
has expired.  The value MUST be cached for possible later use.</t>
<t>ED-55 The endpoint MUST attempt to update its location at the time of an emergency call. If it 
cannot obtain a new location quickly (see <xref target="Location"></xref>), it MUST use the cached 
value.</t>
<t>ED-56 The endpoint SHOULD attempt to update the LoST mapping at the time of an emergency call. 
If it cannot obtain a new mapping quickly, it MUST use the cached value.  If the device cannot update
the LoST mapping and does not have a cached value, it MUST signal an emergency call without a Route header
containing a PSAP URI.</t>
<t>SP-25 Networks MUST be designed so that at least one proxy in the outbound path will recognize emergency calls with a Request URI of 
the service URN in the "sos" tree. An endpoint places a service URN in the Request URI to indicate 
that the endpoint understood the call was an emergency call. A proxy that processes such a call 
looks for the presence of a SIP Route header field with a URI of a PSAP. Absence of such a Route header 
indicates the endpoint was unable to invoke LoST and the proxy MUST perform the LoST mapping and insert 
a Route header field with the URI obtained.</t>
<t>SP-26 To deal with old user agents that predate this specification and with endpoints that do not have 
access to their own location data, a proxy that recognizes a call as an emergency call that is not 
marked as such (see <xref target="Identifying"></xref>) MUST also perform this mapping, with the 
best location it has available for the endpoint. The resulting PSAP URI would be placed in a Route
header with the service URN in the Request URI.</t>
<t>SP-27 Proxy servers performing mapping SHOULD use location obtained from the access network for 
the mapping. If no location is available, a default location (see <xref 
target="DefaultLocation"></xref>) MUST be supplied.</t>
<t>SP-28 A proxy server which attempts mapping and fails to get a mapping MUST provide a default 
mapping. A suitable default mapping would be the mapping obtained previously for the default 
location appropriate for the caller.</t>
<t>ED-57/SP-29 <xref target="RFC3261"></xref> and <xref target="RFC3263"></xref> procedures MUST be 
used to route an emergency call towards the PSAP's URI.</t>
</section><section anchor="Signaling" title="Signaling of emergency calls">
<section anchor="TLS" title="Use of TLS">
<t>ED-58/SP-30 TLS is the primary mechanism used to secure the signaling for emergency calls.  IPsec <xref target="RFC4301"/> MAY be used instead of TLS for any hop.  Either TLS or IPSEC MUST be used when attempting to signal an emergency call.
</t>
<t>ED-59/SP-31 If TLS session establishment is not available, or fails, the call MUST be retried without TLS.</t>
<t>ED-60/SP-32 <xref target="RFC5626"></xref> is RECOMMENDED to maintain persistent 
TLS connections between entities when one of the entity is an endpoint.  Persistent TLS connection between proxies is RECOMMENDED using any suitable mechanism.</t>
<t>ED-61/AN-28 TLS SHOULD be used when attempting to retrieve location (configuration or 
dereferencing) with HELD.  The use of <xref target="RFC5077"></xref> is RECOMMENDED to minimize
the time to establish TLS sessions without keeping server-side state.  IPsec MAY be used instead of TLS.</t>
<t>ED-62/AN-29 When TLS session establishment fails, the location retrieval MUST be retried without TLS.</t>
</section><section anchor="UAsignaling" title="SIP signaling requirements for User Agents">
<t>ED-63 The initial SIP signaling method is an INVITE request:
<list style="numbers">
<t>The Request URI SHOULD be the service URN in the "sos" tree. If the device does not interpret local dial strings, the Request-URI MUST be a dial string URI <xref 
target="RFC4967"></xref> with the dialed digits.</t>
<t>The To header field SHOULD be a service URN in the "sos" tree. If the device 
does not interpret local dial strings, the To: MUST be a dial string URI with the dialed 
digits.</t>
<t>The From header field SHOULD contain the AoR of the caller.</t>
<t>A Route header field SHOULD be present with a PSAP URI obtained from LoST (see <xref 
target="Routing"></xref>). If the device does not interpret dial plans, 
or was unable to obtain a route from a LoST server, no 
such Route header field will be present.</t>
<t>A Contact header field MUST be globally routable, for example a GRUU <xref 
target="RFC5627"></xref>, and be valid for several minutes following the termination of the call, 
provided that the UAC remains registered with the same registrar,
to permit an immediate call-back to the specific device which 
placed the emergency call.  It is acceptable if the UAC inserts a locally routable URI and a subsequent B2BUA
maps that to a globally routable URI.</t>
<t>Other header fields MAY be included as per normal SIP behavior.</t>
<t>If a geolocation URI is included in the INVITE, a Supported header field MUST be included with a 'geolocation-sip' or 'geolocation-http" option tag, as appropriate.
<xref target="I-D.ietf-sipcore-location-conveyance"></xref>.</t>
<t>If a device understands the SIP location conveyance 
<xref target="I-D.ietf-sipcore-location-conveyance"></xref> extension and has its location available, it MUST 
include location either by-value, by-reference or both.</t>
<t>A SDP offer SHOULD be included in the INVITE. If voice is supported the offer SHOULD include 
the G.711 codec, see <xref target="Media"></xref>.  As PSAPs may support a wide range of media types and codecs, sending an offerless INVITE may result in a lengthy return offer, but is permitted.  Cautions in <xref target="RFC3261"/> on offerless INVITEs should be considered before such use.</t>
<t>If the device includes location-by-value, the UA MUST support multipart message bodies, since 
SDP will likely be also in the INVITE.</t>

</list></t>
</section><section anchor="ProxySignaling" title="SIP signaling requirements for proxy servers">
<t>SP-33 SIP Proxy servers processing emergency calls:
<list style="numbers">
<t>If the proxy interprets dial plans on behalf of user agents, the proxy MUST look for 
the local emergency dial string at the location of the end device and MAY look for the home 
dial string. If it finds it, the proxy MUST: 
<list style="symbols">
<t>Insert a Geolocation header field. Location-by-reference MUST be used 
because proxies must not insert bodies.</t>
<t>Insert the Geolocation-Routing header with appropriate parameters .</t>
<t>Map the location to a PSAP URI using LoST.</t>
<t>Add a Route header with the PSAP URI.</t>
<t>Replace the Request-URI (which was the dial string) with the service URN appropriate for 
the emergency dial string.</t>
<t>Route the call using normal SIP routing mechanisms.</t>
</list></t>
<t>If the proxy recognizes the service URN in the Request URI, and does not find a Route
header, it MUST query a LoST server immediately. If a location was provided (which should be the 
case), the proxy uses that location to query LoST.  The proxy may have to dereference a location 
by reference to get a value.  If a location is not present, and the proxy can query a LIS which 
has the location of the UA it MUST do so.  If no location is present, and the proxy does not have 
access to a LIS which could provide location, the proxy MUST supply a default location (See <xref 
target="DefaultLocation"></xref>).  The location (in the signaling, obtained from a LIS, or 
default) MUST be used in a query to LoST with the service URN received with the call.  The 
resulting URI MUST be placed in a Route header added to the call.</t>
<t>The proxy  
MAY add a Geolocation header field. Such an additional location SHOULD NOT be used for routing; the 
location provided by the UA should be used.</t>
<t>Either a P-Asserted-Identity <xref target="RFC3325"></xref> or an Identity header field <xref 
target="RFC4474"></xref>, or both, SHOULD be included to identify the sender. For services which 
must support emergency calls from unauthenticated devices, valid identity may not be available.  Proxies encountering a P-Asserted-Identity will need to pass the header to the PSAP, which is in a different domain. <xref target="RFC3325"/> requires a "spec(T)" to determine what happens if the "id" privacy service, or a Privacy header is present and requests privacy.  In the absence of another spec(T), such proxies should pass the header unmodified if and only if the connection between the proxy and the PSAP is, as far as the proxy can determine, protected by TLS with mutual authentication using keys reliably known by the parties, encrypted with no less strength than AES and the local regulations governing the PSAP do not otherwise specify.</t>
<t>Proxies SHOULD NOT return a 424 error.  It should process the INVITE as best as it can.</t>
<t>Proxies SHOULD NOT obey a Geolocation-Routing value of "no" or a missing value if the proxy must query LoST to obtain a route.  Emergency calls are always routed by location.</t>
</list></t>
</section></section><section anchor="Callbacks" title="Call backs">
<t>ED-64/SP-34 Devices device SHOULD have a globally routable URI in a Contact: header field which remains valid for several minutes
past the time the original call containing the URI completes unless the device registration expires and is not
renewed.</t>
<t>SP-35 Call backs to the Contact: header URI received within 30 minutes of an emergency call
must reach the device regardless of call features or services
that would normally cause the call to be routed to some other entity.</t>
<t>SP-36 Devices MUST have a persistent AOR URI either in a P-Asserted-Identity header field or From protected by 
an Identity header field suitable for returning a call some time after the original call.  Such a call back would not
necessarily reach the device that originally placed the call.</t>
</section><section anchor="MidCall" title="Mid-call behavior">
<t>ED-65/SP-37 During the course of an emergency call, devices and proxies MUST initiate a call transfer upon receipt of REFER 
request within the dialog with method=INVITE and the Referred-by header field <xref target="RFC3515"></xref> in that request. </t>

</section><section anchor="Termination" title="Call termination">
<t>ED-66 Normal <xref target="RFC3261"/> procedures for termination MUST be used for termination of the call.</t>
</section><section anchor="DisableFeatures" title="Disabling of features">
<t>ED-67/SP-38 User Agents and proxies MUST disable features that will interrupt an
ongoing emergency call, such as:
<list style="symbols">
<t>Call Waiting</t>
<t>Call Transfer</t>
<t>Three Way Call</t>
<t>Hold</t>
<t>Outbound Call Blocking</t>
</list>
when an emergency call is established, but see ED-66 with respect to Call Waiting.  Also see ED-74 in <xref target="Media"></xref>.</t>
<t>ED-68/SP-39 The emergency dial strings SHOULD NOT be permitted in Call Forward numbers or speed 
dial lists.</t>
<t>ED-69/SP-40 The User Agent and Proxies MUST disable call features which would interfere with the ability of 
call backs from the PSAP to be completed such as:
<list style="symbols">
<t>Do Not Disturb</t>
<t>Call Forward (all kinds)</t>
</list>
These features SHOULD be disabled for approximately 30 minutes following termination of an emergency call.</t>
<t>ED-70 Call backs SHOULD be determined by retaining the domain of the PSAP which answers an 
outgoing emergency call and instantiating a timer which starts when the call is terminated.  If a 
call is received from the same domain and within the timer period, sent to the Contact: or AoR used 
in the emergency call, it should be assumed to be a call back.  The suggested timer period is 5 
minutes.  <xref target="RFC4916"/> may be used by the PSAP to inform the endpoint of the domain of the PSAP.
Recognizing a call back from the domain of the PSAP will not always work, and further
standardization will be required to give the endpoint the ability to recognize a call back.</t>
</section><section anchor="Media" title="Media">
<t>ED-71 Endpoints MUST send and receive media streams on RTP <xref target="RFC3550"></xref>.</t>
<t>ED-72 Normal SIP offer/answer <xref target="RFC3264"></xref> negotiations MUST be used to agree 
on the media streams to be used.</t>
<t>ED-73/SP-41 G.711 A law (and mu Law if they are intended be used in North America) encoded 
voice as described in <xref target="RFC3551"></xref> MUST be supported.  If the endpoint cannot support G.711, a transcoder MUST be used so that the offer received at the PSAP contains G.711. It is desirable to include wideband codecs such
as G.722 and AMR-WB in the offer.  PSAPs SHOULD support narrowband codecs common on endpoints in their area to avoid transcoding.</t>
<t>ED-74 Silence suppression (Voice Activity Detection methods) MUST NOT be used on emergency 
calls. PSAP call takers sometimes get information on what is happening in the background to 
determine how to process the call.</t>
<t>ED-75 Endpoints supporting Instant Messaging (IM) MUST support either <xref target="RFC3428"></xref> and <xref 
target="RFC4975"></xref>.</t>
<t>ED-76 Endpoints supporting real-time text MUST use <xref target="RFC4103"></xref>. The 
expectations for emergency service support for the real-time text medium are described in <xref 
target="RFC5194"></xref>, Section 7.1.</t>
<t>ED-77 Endpoints supporting video MUST support H.264 per <xref target="RFC6184"></xref>.</t>
</section><section anchor="Testing" title="Testing">
<t>ED-78 INVITE requests to a service URN starting with "test." indicates a request for an 
automated test. For example, "urn:service:test.sos.fire". As in standard SIP, a 200 (OK) response 
indicates that the address was recognized and a 404 (Not found) that it was not. A 486 (Busy Here) 
MUST be returned if the test service is busy, and a 404 (Not found) MUST be returned if 
the PSAP does not support the test mechanism.</t>
<t>ED-79 In its response to the test, the PSAP MAY include a text body (text/plain) indicating the 
identity of the PSAP, the requested service, and the location reported with the call. For the 
latter, the PSAP SHOULD return location-by-value even if the original location delivered with the 
test was by-reference. If the location-by-reference was supplied, and the dereference requires 
credentials, the PSAP SHOULD use credentials supplied by the LIS for test purposes. This alerts the 
LIS that the dereference is not for an actual emergency call and location hiding techniques, if 
they are being used, may be employed for this dereference.  
Use of SIPS for the request would assure the response containing the location is kept private
</t>
<t>ED-80 A PSAP accepting a test call SHOULD accept a media loopback test
<xref target="I-D.ietf-mmusic-media-loopback"></xref> and SHOULD support the "rtp-pkt-loopback" and "rtp-start-loopback" 
options. The user agent would specify a loopback attribute of "loopback-source", the PSAP being the 
mirror. User Agents should expect the PSAP to loop back no more than 3 packets of each media type 
accepted (which limits the duration of the test), after which the PSAP would normally send BYE.</t>
<t>ED-81 User agents SHOULD perform a full call test, including media loopback, after a disconnect 
and subsequent change in IP address not due to a reboot. After an initial test, a full test 
SHOULD be repeated approximately every 30 days with a random interval.</t>
<t>ED-82 User agents MUST NOT place a test call immediately after booting. If the IP address 
changes after booting, the endpoint should wait a random amount of time (in perhaps a 30 minute period, 
sufficient for any avalanche restart to complete) and then test.</t>
<t>ED-83 PSAPs MAY refuse repeated requests for test from the same device in a short period of 
time. Any refusal is signaled with a 486 or 488 response.</t>
</section><section anchor="Security" title="Security Considerations">
<t>Security considerations for emergency calling have been documented in 
<xref target="RFC5069"></xref>, and 
<xref target="RFC6280"></xref>.  This document suggests that security (TLS or IPsec) be used hop by hop on a SIP call to protect location information, identity, etc.  It also suggests that if the attempt to create a security association fails, the call be retried without the security.  It's more important to get an emergency call through than to protect the data; indeed, in many jurisdictions privacy is explicitly waived when making emergency calls.  Placing a call without security may reveal user information, including location.  The alternative - failing the call if security cannot be established, is considered unacceptable.</t>
</section><section title="IANA Considerations">
<t>This document registers service URNs in the Service URN Labels registry per <xref target="RFC5031"/> for testing.</t>
<section title="test service urn">
<t>A new entry in the URN Service Label registry is added.  The new service is "test", the reference is this document, and the description is "self test".</t></section>
<section title="'test' Subregistry">
<t>A new Subregistry is created, the "'test' Sub-Service.  The registration process is Expert Review per <xref target="RFC5226"/>. The expert review should consider that the entries in this registry nominally track the entries in the sos sub registry, although it is not required that every entry in sos have an entry in test, and it is possible that entries in the test sub-registry not necessarily be in the sos sub registry.  For example, testing of non-emergency URNs may be allowed.  The Reference is this document.  The initial content of the subregistry is:</t>
<figure><artwork><![CDATA[
     Service                 Reference             Description
--------------------------------------------------------------------
test.sos                [this document]  test for sos
test.sos.ambulance      [this document]  test for sos.ambulance
test.sos.animal-control [this document]  test for sos.animal-control
test.sos.fire           [this document]  test for sos.fire
test.sos.gas            [this document]  test for sos.gas
test.sos.marine         [this document]  test for sos.marine
test.sos.mountain       [this document]  test for sos.mountain
test.sos.physician      [this document]  test for sos.physician
test.sos.poison         [this document]  test for sos.poison
test.sos.police         [this document]  test for sos.police
]]></artwork></figure></section></section>
<section title="Acknowledgements">
<t>Work group members participating in the creation and review of this document include
Hannes Tschofenig, Ted Hardie, Marc Linsner, Roger Marshall, Stu Goldman, Shida Schubert, James 
Winterbottom, Barbara Stark, Richard Barnes and Peter Blatherwick.</t>
    </section>
  </middle>

  <back>
    <references title="Normative References">
      &rfc2119;
      &rfc3118;
      &rfc3261;
      &rfc3263;
      &rfc3264;
      &rfc3265;
      &rfc3428;
      &rfc5389;
      &rfc3515;
      &rfc3550;
      &rfc3551;
      &rfc3856;
      &rfc3966;
      &rfc4103;
      &rfc4119;
      &rfc4301;
      &rfc4474;
      &rfc4776;
      &rfc4916;
      &rfc4967;
      &rfc4975;
      &rfc5031;
      &rfc5139;
      &rfc5222;
      &rfc5223;
      &rfc5226;
      &rfc5491;
      &rfc5626;
      &rfc5627;
      &rfc5746;
      &rfc5751;
      &rfc5985;
      &rfc5986;
      &rfc6184;
      &rfc6225;
      &draft-ietf-sipcore-location-conveyance;
      &draft-ietf-mmusic-media-loopback;
      <reference anchor="LLDP-MED">
        <front>
          <title>ANSI/TIA-1057 Link Layer Discovery Protocol - Media Endpoint
          Discovery</title>

          <author fullname="">
            <organization>TIA</organization>
          </author>

          <date year="" />
        </front>
      </reference>
    </references>
    <references title="Informative References">
      &rfc3325;
      &rfc5012;
      &rfc5069;
      &rfc5077;
      &rfc5194;
      &rfc6280;
      &draft-ietf-ecrit-framework;
     </references>

</back>
</rfc>

