Baseline Encoding and Transport of Pre-Congestion Information
RFC 5696

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Network Working Group                                       T. Moncaster
Request for Comments: 5696                                    B. Briscoe
Category: Standards Track                                             BT
                                                                M. Menth
                                                 University of Wuerzburg
                                                           November 2009

     Baseline Encoding and Transport of Pre-Congestion Information

Abstract

   The objective of the Pre-Congestion Notification (PCN) architecture
   is to protect the quality of service (QoS) of inelastic flows within
   a Diffserv domain.  It achieves this by marking packets belonging to
   PCN-flows when the rate of traffic exceeds certain configured
   thresholds on links in the domain.  These marks can then be evaluated
   to determine how close the domain is to being congested.  This
   document specifies how such marks are encoded into the IP header by
   redefining the Explicit Congestion Notification (ECN) codepoints
   within such domains.  The baseline encoding described here provides
   only two PCN encoding states: Not-marked and PCN-marked.  Future
   extensions to this encoding may be needed in order to provide more
   than one level of marking severity.

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (c) 2009 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
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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 BSD License.

Moncaster, et al.           Standards Track                     [Page 1]
RFC 5696                 Baseline PCN Encoding             November 2009

   This document may contain material from IETF Documents or IETF
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   Without obtaining an adequate license from the person(s) controlling
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   than English.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Requirements Notation  . . . . . . . . . . . . . . . . . . . .  3
   3.  Terminology and Abbreviations  . . . . . . . . . . . . . . . .  3
     3.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
     3.2.  List of Abbreviations  . . . . . . . . . . . . . . . . . .  4
   4.  Encoding Two PCN States in IP  . . . . . . . . . . . . . . . .  4
     4.1.  Marking Packets  . . . . . . . . . . . . . . . . . . . . .  5
     4.2.  Valid and Invalid Codepoint Transitions  . . . . . . . . .  6
     4.3.  Rationale for Encoding . . . . . . . . . . . . . . . . . .  7
     4.4.  PCN-Compatible Diffserv Codepoints . . . . . . . . . . . .  7
       4.4.1.  Co-Existence of PCN and Not-PCN Traffic  . . . . . . .  8
   5.  Rules for Experimental Encoding Schemes  . . . . . . . . . . .  8
   6.  Backward Compatibility . . . . . . . . . . . . . . . . . . . .  9
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   8.  Conclusions  . . . . . . . . . . . . . . . . . . . . . . . . . 10
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 10
     10.2. Informative References . . . . . . . . . . . . . . . . . . 10
   Appendix A.  PCN Deployment Considerations (Informative) . . . . . 11
     A.1.  Choice of Suitable DSCPs . . . . . . . . . . . . . . . . . 11
     A.2.  Rationale for Using ECT(0) for Not-Marked  . . . . . . . . 12
   Appendix B.  Co-Existence of PCN and ECN (Informative) . . . . . . 13

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