Internet Engineering Task Force                           G. Karagiannis 
Internet-Draft                                      University of Twente
Intended status: Informational                                 T. Taylor
Expires: August 08, 2012                                          Huawei
                                                                 K. Chan
                                                              Consultant
                                                                M. Menth
                                                 University of Tuebingen
                                                              P. Eardley
                                                                      BT
                                                       February 08, 2012
                                                                        
                                                                        
                                                                        
                                                                        


    Requirements for Signaling of (Pre-) Congestion Information in a  
                           DiffServ Domain
                  draft-ietf-pcn-signaling-requirements-08

Abstract

   Precongestion notification (PCN) is a means for protecting quality of
   service for inelastic traffic admitted to a Diffserv domain. The 
   overall PCN architecture is described in RFC 5559. This memo 
   describes the requirements for the signaling applied within the PCN 
   domain: (1) PCN-feedback-information is carried from the PCN-egress-
   node to the decision point;(2) the decision point may ask the PCN-
   ingress-node to measure, and report back, the rate of sent PCN-
   traffic between that PCN-ingress-node and PCN-egress-node. The
   decision point may be either collocated with the PCN-ingress-node or
   a centralized node (in the first case, (2) is not required). The
   signaling requirements pertain in particular to two edge behaviors,
   "controlled load (CL)" and "single marking (SM)".




Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on August 08, 2012.
   

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Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
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   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].


Table of Contents
1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.  Signaling Requirements for Messages from the PCN-Egress-Nodes to 
    Decision Point(s) . . . . . . . . . . . . . . . . . . . . . . . .  3
3.  Signaling Requirements for Messages between Decision Point(s) and 
    PCN-Ingress-Nodes . . . . . . . . . . . . . . . . . . . . . . . .  5
4.  Security Considerations . . . . . . . . . . . . . . . . . . . . .  5
5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . .  6
6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . .  . 6
7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
    7.1.  Normative References . . . . . . . . . . . . . . . . . . . . 6
    7.2.  Informative References . . . . . . . . . . . . . . . . . . . 6
    Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . .   7
















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1.  Introduction

   The main objective of Pre-Congestion Notification (PCN) is to support
   the quality of service (QoS) of inelastic flows within a Diffserv 
   domain in a simple, scalable, and robust fashion.  Two mechanisms 
   are used: admission control and flow termination. Admission control 
   is used to decide whether to admit or block a new flow request while 
   flow termination is used in abnormal circumstances to decide
   whether to terminate some of the existing flows.  To support these 
   two features, the overall rate of PCN-traffic is metered on every 
   link in the domain, and PCN-packets are appropriately marked when 
   certain configured rates are exceeded. These configured rates are 
   below the rate of the link thus providing notification to boundary 
   nodes about overloads before any congestion occurs (hence "pre-
   congestion" notification). The PCN-egress-nodes measure the rates of 
   differently marked PCN traffic in periodic intervals and report these 
   rates to the decision points for admission control and flow 
   termination, based on which they take their decisions. The decision 
   points may be collocated with the PCN-ingress-nodes or their function 
   may be implemented in a centralized node.
   For more details see [RFC5559],
   [draft-ietf-pcn-cl-edge-behaviour-11], 
   [draft-ietf-pcn-sm-edge-behaviour-08].

   This memo specifies the requirements on signaling protocols:
   o to carry reports from a PCN-egress-node to the decision point,
   o to carry requests, from the decision point to a PCN-ingress-node, 
     that trigger the PCN-ingress-node to measure the PCN-sent-rate,
   o to carry reports, from a PCN-ingress-node to the decision 
     point.

   The latter two messages are only needed if the decision point and
   PCN-ingress-node are not collocated.
   

2.  Signaling Requirements for Messages from the PCN-Egress-Nodes to 
    Decision Point(s)

   The PCN-egress-node measures per ingress-egress-aggregate the rates 
   of differently marked PCN-traffic in regular intervals. The 
   measurement intervals are recommended to take a fixed value between 
   100 ms and 500 ms, see [draft-ietf-pcn-cl-edge-behaviour-11], 
   [draft-ietf-pcn-sm-edge-behaviour-08]. At the end of each measurement
   interval, the PCN-egress-node calculates the congestion-level-
   estimate (CLE) based on these quantities. 

   The PCN-egress-node MAY be configured to record a set of identifiers 
   of PCN-flows for which it received excess-traffic-marked packets 
   during the last measurement interval.  The latter may be useful to 
   perform flow termination in networks with multipath routing.

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   At the end of each measurement interval, or less frequently if 
   "optional report suppression" is activated, see 

   [draft-ietf-pcn-cl-edge-behaviour-11], [draft-ietf-pcn-sm-edge- 
   behaviour-08], the PCN-egress-node sends a report to the decision 
   point. 

   For the SM edge behavior, the report MUST contain:
   o identifier of the PCN-ingress-node and the identifier of the 
     PCN-egress-node (typically their IP addresses); together they 
     specify the ingress-egress-aggregate to which the report refers,
   o rate of not-marked PCN-traffic (NM-rate) in octets/second,
   o rate of PCN-marked traffic (PM-rate) in octets/second,

   For the CL edge behavior, the report MUST contain:
   o identifier of the PCN-ingress-node and the identifier of the 
     PCN-egress-node (typically their IP addresses); together they 
     specify the ingress-egress-aggregate to which the report refers,
   o rate of not-marked PCN-traffic (NM-rate) in octets/second,
   o rate of threshold-marked PCN traffic (ThM-rate) in 
     octets/second,
   o rate of excess-traffic-marked traffic (ETM-rate) in octets/second,

   The number format and the rate units used by the signaling protocol 
   will limit the maximum rate that PCN can use.  If signaling space is
   tight it might be reasonable to impose a limit, but any such limit
   may impose unnecessary constraints in future.

   The signaling report can either be sent directly to the decision 
   point or it can "piggy-back", i.e., be included within some other 
   message that passes through the PCN-egress-node and then reaches the 
   decision point. 
 
   As described in [draft-ietf-pcn-cl-edge-behaviour-11], PCN reports  
   from the PCN-egress-node to the decision point may contain flow 
   identifiers for individual flows within an ingress-egress-
   aggregate that have recently experienced excess-marking. Hence, 
   the PCN report messages used by the PCN CL edge behavior MUST be 
   capable of carrying sequences of octet strings constituting such 
   identifiers."

   Signaling messages SHOULD have a higher priority and a lower drop  
   precedence than PCN-packets, see [RFC5559], to deliver them quickly 
   and to avoid that they are dropped in case of overload.

   The load generated by the signaling protocol SHOULD be minimized.  We
   give three examples that may help to achieve that goal:
   o piggy-backing the reports by the PCN-egress-nodes to the decision      
     point(s) onto other signaling messages that are already in place,
   o reducing the amount of reports to be sent by optional report 
     suppression,
   o combining reports for different ingress-egress-aggregates in a 
     single message (if they are for the same decision point).

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   As PCN reports are sent regularly, additional reliability mechanisms    
   are not needed. This also holds in the presence of optional report 
   suppression as reports are sent periodically if actions by the  
   decision point(s) are needed, see [draft-ietf-pcn-cl-edge-behaviour-
   -11], [draft-ietf-pcn-sm-edge-behaviour-08].


3.  Signaling Requirements for Messages between Decision Point(s) and 
    PCN-Ingress-Nodes 

   Through request-response signaling between the decision point and
   PCN-ingress-node, the decision point requests and in response the
   PCN-ingress-node measures and reports the PCN-sent-rate for a
   specific ingress-egress-aggregate. Signaling is needed only if the
   decision point and PCN-ingress-node are not collocated. 

   The request MUST contain:
   o the identifier of the PCN-ingress-node and the identifier of the  
     PCN-egress-node; together they determine the ingress-egress-
     aggregate for which the PCN-sent-rate is requested,
   o the identifier of the decision point that requests the PCN-sent-
     rate.

   The report MUST contain:
   o the PCN-sent-rate in octets/second,
   o the identifier of the PCN-ingress-node and the identifier of the 
     PCN-egress-node. 

   The request MUST be addressed to the PCN-ingress-node, and the report
   MUST be addressed to the decision point that requested it.

   The request and the report SHOULD be sent with high priority, a lower 
   drop precedence than PCN-packets, and reliably, because they are sent 
   only when flow termination is needed, which is an urgent action. 

   Note that a complete system description for a PCN domain with 
   centralized Decision Point includes the signaling from Decision Point 
   to the PCN-ingress-nodes to control flow admission and termination. 
   However, this is a known problem whose solutions were given by, 
   for example, [RFC3084] or [RFC5431], and it lies outside the scope of 
   the present document.


4.  Security Considerations

   [RFC5559] provides a general description of the security  
   considerations for PCN. This memo relies on the security related 
   requirements on the PCN signaling, provided in [RFC5559].  In 
   particular, the signaling between the PCN-boundary-nodes must be  
   protected from attacks.  For example, the recipient needs to 
   validate that the message is indeed from the node that claims to have 
   sent it. Possible measures include digest authentication and 
   protection against replay and man-in-the-middle attacks.

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   For the generic aggregate RSVP protocol, specifically, additional 
   protection methods against security attacks are described in 
  [RFC4860].


5.  IANA Considerations

   This memo includes no request to IANA.


6.  Acknowledgments

   We would like to acknowledge the members of the PCN working group for
   the discussions that produced the contents of this memo.


7.  References

7.1.  Normative References

   [RFC2119]  S. Bradner, "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5559]  P., Eardley, "Pre-Congestion Notification (PCN)
              Architecture", RFC 5559, June 2009.

   [draft-ietf-pcn-cl-edge-behaviour-11] T. Taylor, A, Charny, 
              F. Huang, G. Karagiannis, M. Menth, "PCN Boundary Node 
              Behaviour for the Controlled Load (CL) Mode of Operation 
              (Work in progress)", December 2011.

   [draft-ietf-pcn-sm-edge-behaviour-08] A. Charny, J. Zhang, 
              G.  Karagiannis, M. Menth, T. Taylor, "PCN Boundary Node 
              Behaviour for the Single Marking (SM) Mode of Operation 
              (Work in progress)", December 2011.


7.2.  Informative References

   [RFC3084]  K. Chan, J. Seligson, D. Durham, S. Gai, K. McCloghrie, S.  
              Herzog, F. Reichmeyer, R. Yavatkar, A. Smith, "COPS Usage 
              for Policy Provisioning (COPS-PR)", RFC 3084, March 2001.

   [RFC4860]  F. Le Faucheur, B. Davie, P. Bose, C. Christou, M. 
              Davenport, "Generic Aggregate Resource ReSerVation 
              Protocol (RSVP) Reservations", RFC 4860, May 2007.

   [RFC5431]  D. Sun, "Diameter ITU-T Rw Policy Enforcement Interface 
              Application", RFC 5431, March 2009.



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Authors' Addresses

   Georgios Karagiannis
   University of Twente
   P.O. Box 217
   7500 AE Enschede,  
   The Netherlands 
   EMail: g.karagiannis@utwente.nl  

   Tom Taylor 
   Huawei Technologies
   1852 Lorraine Ave.
   Ottawa, Ontario  K1H 6Z8
   Canada
   Phone: +1 613 680 2675
   Email: tom.taylor.stds@gmail.com

   Kwok Ho Chan
   Consultant

   Email: khchan.work@gmail.com

   Michael Menth
   University of Tuebingen
   Department of Computer Science
   Chair of Communication Networks
   Sand 13
   72076 Tuebingen
   Germany
   Phone: +49 7071 29 70505
   Email: menth@informatik.uni-tuebingen.de

   Philip Eardley
   BT
   B54/77, Sirius House Adastral Park Martlesham Heath
   Ipswich, Suffolk  IP5 3RE
   United Kingdom
   EMail: philip.eardley@bt.com















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