Differentiated Services (Diffserv) and Real-Time Communication
RFC 7657

Document Type RFC - Informational (November 2015; No errata)
Last updated 2015-11-18
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Stream WG state Submitted to IESG for Publication Aug 2014
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IESG IESG state RFC 7657 (Informational)
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Internet Engineering Task Force (IETF)                     D. Black, Ed.
Request for Comments: 7657                                           EMC
Category: Informational                                         P. Jones
ISSN: 2070-1721                                                    Cisco
                                                           November 2015

     Differentiated Services (Diffserv) and Real-Time Communication

Abstract

   This memo describes the interaction between Differentiated Services
   (Diffserv) network quality-of-service (QoS) functionality and real-
   time network communication, including communication based on the
   Real-time Transport Protocol (RTP).  Diffserv is based on network
   nodes applying different forwarding treatments to packets whose IP
   headers are marked with different Diffserv Codepoints (DSCPs).
   WebRTC applications, as well as some conferencing applications, have
   begun using the Session Description Protocol (SDP) bundle negotiation
   mechanism to send multiple traffic streams with different QoS
   requirements using the same network 5-tuple.  The results of using
   multiple DSCPs to obtain different QoS treatments within a single
   network 5-tuple have transport protocol interactions, particularly
   with congestion control functionality (e.g., reordering).  In
   addition, DSCP markings may be changed or removed between the traffic
   source and destination.  This memo covers the implications of these
   Diffserv aspects for real-time network communication, including
   WebRTC.

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/rfc7657.

Black & Jones                 Informational                     [Page 1]
RFC 7657              Diffserv and RT Communication        November 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.  Real-Time Communications  . . . . . . . . . . . . . . . . . .   3
     2.1.  RTP Background  . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  RTP Multiplexing  . . . . . . . . . . . . . . . . . . . .   6
   3.  Differentiated Services (Diffserv)  . . . . . . . . . . . . .   7
     3.1.  Diffserv Per-Hop Behaviors (PHBs) . . . . . . . . . . . .  10
     3.2.  Traffic Classifiers and DSCP Remarking  . . . . . . . . .  10
   4.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  12
   5.  Diffserv Interactions . . . . . . . . . . . . . . . . . . . .  13
     5.1.  Diffserv, Reordering, and Transport Protocols . . . . . .  13
     5.2.  Diffserv, Reordering, and Real-Time Communication . . . .  15
     5.3.  Drop Precedence and Transport Protocols . . . . . . . . .  16
     5.4.  Diffserv and RTCP . . . . . . . . . . . . . . . . . . . .  17
   6.  Guidelines  . . . . . . . . . . . . . . . . . . . . . . . . .  18
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  20
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  20
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  22
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  26
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

Black & Jones                 Informational                     [Page 2]
RFC 7657              Diffserv and RT Communication        November 2015

1.  Introduction

   This memo describes the interactions between Differentiated Services
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