Supplemental Information for the New Definition of the EF PHB (Expedited Forwarding Per-Hop Behavior) (RFC3247)

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. ...