Browse Prior Art Database

Assured Forwarding PHB Group (RFC2597) Disclosure Number: IPCOM000003184D
Original Publication Date: 1999-Jun-01
Included in the Prior Art Database: 2019-Feb-11
Document File: 11 page(s) / 15K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

J. Heinanen: AUTHOR [+3]

Related Documents

10.17487/RFC2597: DOI


This document defines a general use Differentiated Services (DS) Per-Hop-Behavior (PHB) Group called Assured Forwarding (AF). [STANDARDS-TRACK]

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 16% of the total text.

Network Working Group J. Heinanen Request for Comments: 2597 Telia Finland Category: Standards Track F. Baker Cisco Systems W. Weiss Lucent Technologies J. Wroclawski MIT LCS June 1999

Assured Forwarding PHB Group

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 Notice

Copyright (C) The Internet Society (1999). All Rights Reserved.


This document defines a general use Differentiated Services (DS) [Blake] Per-Hop-Behavior (PHB) Group called Assured Forwarding (AF). The AF PHB group provides delivery of IP packets in four independently forwarded AF classes. Within each AF class, an IP packet can be assigned one of three different levels of drop precedence. A DS node does not reorder IP packets of the same microflow if they belong to the same AF class.

1. Purpose and Overview

There is a demand to provide assured forwarding of IP packets over the Internet. In a typical application, a company uses the Internet to interconnect its geographically distributed sites and wants an assurance that IP packets within this intranet are forwarded with high probability as long as the aggregate traffic from each site does not exceed the subscribed information rate (profile). It is desirable that a site may exceed the subscribed profile with the understanding that the excess traffic is not delivered with as high probability as the traffic that is within the profile. It is also

Heinanen Standards Track [Page 1]

RFC 2597 Assured Forwarding PHB Group June 1999

important that the network does not reorder packets that belong to the same microflow, as defined in [Nichols], no matter if they are in or out of the profile.

Assured Forwarding (AF) PHB group is a means for a provider DS domain to offer different levels of forwarding assurances for IP packets received from a customer DS domain. Four AF classes are defined, where each AF class is in each DS node allocated a certain amount of forwarding resources (buffer space and bandwidth). IP packets that wish to use the services provided by the AF PHB group are assigned by the customer or the provider DS domain into one or more of these AF classes according to the services that the customer has subscribed to. Further background about this capability and some ways to use it may be found in [Clark].

Within each AF class IP packets are marked (again by the customer or the provider DS domain) with one of three possible drop precedence values. In case of congestion, the drop precedence of a packet determines the relative importance of the packet within the AF class. A congested DS node tries to protect packets with a lower drop precedence value from being lost by preferably discarding packets with a higher d...