Supplemental Information for the New Definition of the EF PHB (Expedited Forwarding Per-Hop Behavior)
RFC 3247

Document Type RFC - Informational (March 2002; Errata)
Last updated 2013-03-02
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Network Working Group                                          A. Charny
Request for Comments: 3247                           Cisco Systems, Inc.
Category: Informational                                   J.C.R. Bennett
                                                                Motorola
                                                               K. Benson
                                                                 Tellabs
                                                          J.Y. Le Boudec
                                                                    EPFL
                                                                 A. Chiu
                                                         Celion Networks
                                                             W. Courtney
                                                                     TRW
                                                               S. Davari
                                                              PMC-Sierra
                                                               V. Firoiu
                                                         Nortel Networks
                                                             C. Kalmanek
                                                           AT&T Research
                                                       K.K. Ramakrishnan
                                                      TeraOptic Networks
                                                              March 2002

            Supplemental Information for the New Definition
         of the EF PHB (Expedited Forwarding Per-Hop Behavior)

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

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

Abstract

   This document was written during the process of clarification of
   RFC2598 "An Expedited Forwarding PHB" that led to the publication of
   revised specification of EF "An Expedited Forwarding PHB".  Its
   primary motivation is providing additional explanation to the revised
   EF definition and its properties.  The document also provides
   additional implementation examples and gives some guidance for
   computation of the numerical parameters of the new definition for
   several well known schedulers and router architectures.

Charny, et. al.              Informational                      [Page 1]
RFC 3247                Supplemental Information              March 2002

Table of Contents

   1      Introduction  ...........................................   2
   2      Definition of EF PHB  ...................................   3
   2.1    The formal definition  ..................................   3
   2.2    Relation to Packet Scale Rate Guarantee  ................   6
   2.3    The need for dual characterization of EF PHB  ...........   7
   3      Per Packet delay  .......................................   9
   3.1    Single hop delay bound  .................................   9
   3.2    Multi-hop worst case delay  .............................  10
   4      Packet loss  ............................................  10
   5      Implementation considerations  ..........................  11
   5.1    The output buffered model with EF FIFO at the output.  ..  12
   5.1.1  Strict Non-preemptive Priority Queue  ...................  12
   5.1.2  WF2Q  ...................................................  13
   5.1.3  Deficit Round Robin (DRR)  ..............................  13
   5.1.4  Start-Time Fair Queuing and Self-Clocked Fair Queuing  ..  13
   5.2    Router with Internal Delay and EF FIFO at the output  ...  13
   6      Security Considerations  ................................  14
   7      References  .............................................  14
   Appendix A. Difficulties with the RFC 2598 EF PHB Definition  ..  16
   Appendix B. Alternative Characterization of Packet Scale Rate
               Guarantee  .........................................  20
   Acknowledgements  ..............................................  22
   Authors' Addresses  ............................................  22
   Full Copyright Statement  ......................................  24

1. Introduction

   The Expedited Forwarding (EF) Per-Hop Behavior (PHB) was designed to
   be used to build a low-loss, low-latency, low-jitter, assured
   bandwidth service.  The potential benefits of this service, and
   therefore the EF PHB, are enormous.  Because of the great value of
   this PHB, it is critical that the forwarding behavior required of and
   delivered by an EF-compliant node be specific, quantifiable, and
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