An Expedited Forwarding PHB (Per-Hop Behavior)
RFC 3246

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Network Working Group                                           B. Davie
Request for Comments: 3246                                     A. Charny
Obsoletes: 2598                                      Cisco Systems, Inc.
Category: Standards Track                                 J.C.R. Bennett
                                                                Motorola
                                                               K. Benson
                                                                 Tellabs
                                                          J.Y. Le Boudec
                                                                    EPFL
                                                             W. Courtney
                                                                     TRW
                                                               S. Davari
                                                              PMC-Sierra
                                                               V. Firoiu
                                                         Nortel Networks
                                                            D. Stiliadis
                                                     Lucent Technologies
                                                              March 2002

             An Expedited Forwarding PHB (Per-Hop Behavior)

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) The Internet Society (2001).  All Rights Reserved.

Abstract

   This document defines a PHB (per-hop behavior) called Expedited
   Forwarding (EF).  The PHB is a basic building block in the
   Differentiated Services architecture.  EF is intended to provide a
   building block for low delay, low jitter and low loss services by
   ensuring that the EF aggregate is served at a certain configured
   rate.  This document obsoletes RFC 2598.

Davie, et. al.              Standards Track                     [Page 1]
RFC 3246              An Expedited Forwarding PHB             March 2002

Table of Contents

   1      Introduction  ...........................................   2
   1.1    Relationship to RFC 2598  ...............................   3
   2      Definition of EF PHB  ...................................   3
   2.1    Intuitive Description of EF  ............................   3
   2.2    Formal Definition of the EF PHB  ........................   5
   2.3    Figures of merit  .......................................   8
   2.4    Delay and jitter  .......................................   8
   2.5    Loss  ...................................................   9
   2.6    Microflow misordering  ..................................   9
   2.7    Recommended codepoint for this PHB  .....................   9
   2.8    Mutability  .............................................  10
   2.9    Tunneling  ..............................................  10
   2.10   Interaction with other PHBs  ............................  10
   3      Security Considerations  ................................  10
   4      IANA Considerations  ....................................  11
   5      Acknowledgments  ........................................  11
   6      References  .............................................  11
   Appendix: Implementation Examples ..............................  12
   Authors' Addresses .............................................  14
   Full Copyright Statement .......................................  16

1. Introduction

   Network nodes that implement the differentiated services enhancements
   to IP use a codepoint in the IP header to select a per-hop behavior
   (PHB) as the specific forwarding treatment for that packet [3, 4].
   This memo describes a particular PHB called expedited forwarding
   (EF).

   The intent of the EF PHB is to provide a building block for low loss,
   low delay, and low jitter services.  The details of exactly how to
   build such services are outside the scope of this specification.

   The dominant causes of delay in packet networks are fixed propagation
   delays (e.g. those arising from speed-of-light delays) on wide area
   links and queuing delays in switches and routers.  Since propagation
   delays are a fixed property of the topology, delay and jitter are
   minimized when queuing delays are minimized.  In this context, jitter
   is defined as the variation between maximum and minimum delay.  The
   intent of the EF PHB is to provide a PHB in which suitably marked
   packets usually encounter short or empty queues.  Furthermore, if
   queues remain short relative to the buffer space available, packet