RFC 3246 (rfc3246) - Page 2 of 16
An Expedited Forwarding PHB (Per-Hop Behavior)
Alternative Format: Original Text Document
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
loss is also kept to a minimum.
Davie, et. al. Standards Track