Supplemental Information for the New Definition of the EF PHB (Expedited Forwarding Per-Hop Behavior)
RFC 3247
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RFC - Informational
(March 2002; Errata)
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2020-01-21
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RFC 3247 (Informational)
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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
unambiguous.
Unfortunately, the definition of EF PHB in the original RFC2598 [10]
was not sufficiently precise (see Appendix A and [4]). A more
precise definition is given in [6]. This document is intended to aid
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