RFC 3247 (rfc3247) - Page 2 of 24

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

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
   unambiguous.

   Unfortunately, the definition of EF PHB in the original RFC 2598 [10]
   was not sufficiently precise (see Appendix A and [4]).  A more
   precise definition is given in [6].  This document is intended to aid
   in the understanding of the properties of the new definition and
   provide supplemental information not included in the text of [6] for
   sake of brevity.

   This document is outlined as follows.  In section 2, we briefly
   restate the definition for EF PHB of [6].  We then provide some
   additional discussion of this definition and describe some of its
   properties.  We discuss the issues associated with per-packet delay



Charny, et. al.              Informational