Congestion Exposure (ConEx) Concepts, Abstract Mechanism, and Requirements
RFC 7713

Document Type RFC - Informational (December 2015; No errata)
Last updated 2015-12-28
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Internet Engineering Task Force (IETF)                         M. Mathis
Request for Comments: 7713                                  Google, Inc.
Category: Informational                                       B. Briscoe
ISSN: 2070-1721                                                       BT
                                                           December 2015

       Congestion Exposure (ConEx) Concepts, Abstract Mechanism,
                            and Requirements

Abstract

   This document describes an abstract mechanism by which senders inform
   the network about the congestion recently encountered by packets in
   the same flow.  Today, network elements at any layer may signal
   congestion to the receiver by dropping packets or by Explicit
   Congestion Notification (ECN) markings, and the receiver passes this
   information back to the sender in transport-layer feedback.  The
   mechanism described here enables the sender to also relay this
   congestion information back into the network in-band at the IP layer,
   such that the total amount of congestion from all elements on the
   path is revealed to all IP elements along the path, where it could,
   for example, be used to provide input to traffic management.  This
   mechanism is called Congestion Exposure, or ConEx.  The companion
   document, "Congestion Exposure (ConEx) Concepts and Use Cases"
   (RFC 6789), provides the entry point to the set of ConEx
   documentation.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7713.

Mathis & Briscoe              Informational                     [Page 1]
RFC 7713          ConEx Concepts and Abstract Mechanism    December 2015

Copyright Notice

   Copyright (c) 2015 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   6
   3.  Requirements for the ConEx Abstract Mechanism . . . . . . . .   7
     3.1.  Requirements for ConEx Signals  . . . . . . . . . . . . .   7
     3.2.  Constraints on the Audit Function . . . . . . . . . . . .   8
     3.3.  Requirements for Non-abstract ConEx Specifications  . . .   9
   4.  Encoding Congestion Exposure  . . . . . . . . . . . . . . . .  12
     4.1.  Naive Encoding  . . . . . . . . . . . . . . . . . . . . .  12
     4.2.  Null Encoding . . . . . . . . . . . . . . . . . . . . . .  13
     4.3.  ECN-Based Encoding  . . . . . . . . . . . . . . . . . . .  13
     4.4.  Independent Bits  . . . . . . . . . . . . . . . . . . . .  14
     4.5.  Codepoint Encoding  . . . . . . . . . . . . . . . . . . .  14
     4.6.  Units Implied by an Encoding  . . . . . . . . . . . . . .  15
   5.  Congestion Exposure Components  . . . . . . . . . . . . . . .  16
     5.1.  Network Devices (Not Modified)  . . . . . . . . . . . . .  16
     5.2.  Modified Senders  . . . . . . . . . . . . . . . . . . . .  16
     5.3.  Receivers (Optionally Modified) . . . . . . . . . . . . .  17
     5.4.  Policy Devices  . . . . . . . . . . . . . . . . . . . . .  17
       5.4.1.  Congestion Monitoring Devices . . . . . . . . . . . .  18
       5.4.2.  Rest-of-Path Congestion Monitoring  . . . . . . . . .  18
       5.4.3.  Congestion Policers . . . . . . . . . . . . . . . . .  18
     5.5.  Audit . . . . . . . . . . . . . . . . . . . . . . . . . .  19
   6.  Support for Incremental Deployment  . . . . . . . . . . . . .  23
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  25
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