An Expedited Forwarding PHB (RFC2598)
Original Publication Date: 1999-Jun-01
Included in the Prior Art Database: 2000-Sep-13
Internet Society Requests For Comment (RFCs)
V. Jacobson: AUTHOR [+3]
The definition of PHBs (per-hop forwarding behaviors) is a critical part of the work of the Diffserv Working Group. This document describes a PHB called Expedited Forwarding. We show the generality of this PHB by noting that it can be produced by more than one mechanism and give an example of its use to produce at least one service, a Virtual Leased Line. A recommended codepoint for this PHB is given.
Network Working Group V. Jacobson
Request for Comments: 2598 K. Nichols
Category: Standards Track Cisco Systems
An Expedited Forwarding PHB
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright (C) The Internet Society (1999). All Rights Reserved.
The definition of PHBs (per-hop forwarding behaviors) is a critical
part of the work of the Diffserv Working Group. This document
describes a PHB called Expedited Forwarding. We show the generality
of this PHB by noting that it can be produced by more than one
mechanism and give an example of its use to produce at least one
service, a Virtual Leased Line. A recommended codepoint for this PHB
A pdf version of this document is available at
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 [RFC2474,
RFC2475]. This memo describes a particular PHB called expedited
forwarding (EF). The EF PHB can be used to build a low loss, low
latency, low jitter, assured bandwidth, end-to-end service through DS
domains. Such a service appears to the endpoints like a point-to-
point connection or a "virtual leased line". This service has also
been described as Premium service [2BIT].
Loss, latency and jitter are all due to the queues traffic
experiences while transiting the network. Therefore providing low
loss, latency and jitter for some traffic aggregate means ensuring
that the aggregate sees no (or very small) queues. Queues arise when
(short-term) traffic arrival rate exceeds departure rate at some
node. Thus a service that ensures no queues for some aggregate is
equivalent to bounding rates such that, at every transit node, the
aggregate's maximum arrival rate is less than that aggregate's
minimum departure rate.
Creating such a service has two parts:
1) Configuring nodes so that the aggregate has a well-defined
minimum departure rate. ("Well-defined" means independent of
the dynamic state of the node. In particular, independent of
the intensity of other traffic at the node.)
2) Conditioning the aggregate (via policing and shaping) so ...