Current Meeting Report

2.7.3 Differentiated Services (diffserv)

NOTE: This charter is a snapshot of the 52nd IETF Meeting in Salt Lake City, Utah USA. It may now be out-of-date. Last Modified: 09-Oct-01
Brian Carpenter <>
Kathleen Nichols <>
Transport Area Director(s):
Scott Bradner <>
Allison Mankin <>
Transport Area Advisor:
Scott Bradner <>
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Description of Working Group:
There is a clear need for relatively simple and coarse methods of providing differentiated classes of service for Internet traffic, to support various types of applications, and specific business requirements. The differentiated services approach to providing quality of service in networks employs a small, well-defined set of building blocks from which a variety of aggregate behaviors may be built. A small bit-pattern in each packet, in the IPv4 TOS octet or the IPv6 Traffic Class octet, is used to mark a packet to receive a particular forwarding treatment, or per-hop behavior, at each network node. A common understanding about the use and interpretation of this bit-pattern is required for inter-domain use, multi-vendor interoperability, and consistent reasoning about expected aggregate behaviors in a network. Thus, the Working Group has standardized a common layout for a six-bit field of both octets, called the 'DS field'. RFC 2474 and RFC 2475 define the architecture, and the general use of bits within the DS field (superseding theIPv4 TOS octet definitions of RFC 1349).

The Working Group has standardized a small number of specific per-hop behaviors (PHBs), and recommended a particular bit pattern or 'code-point' of the DS field for each one, in RFC 2474, RFC 2597, and RFC 2598. No more PHBs will be standardized until all the current milestones of the WG have been satisfied and the existing standard PHBs have been promoted at least to Draft Standard status.

The WG has investigated the additional components necessary to support differentiated services, including such traffic conditioners as traffic shapers and packet markers that could be used at the boundaries of networks. There are many examples of these in the technical literature.

The WG will define a general conceptual model for boundary devices, including traffic conditioning parameters, and configuration and monitoring data. It is expected that a subset of this will apply to all diffserv nodes. The group will also define a MIB and a PIB for diffserv nodes, and an encoding to identify PHBs in protocol messages. It will document issues involving diffserv through tunnels.

The WG will develop a format for precisely describing various Per-Domain Behaviors (PDBs). A PDB is a collection of packets with the same codepoint, thus receiving the same PHB, traversing from edge to edge of a single diffserv network or domain. Associated with each PDB are measurable, quantifiable characteristics which can be used to describe what happens to packets of that PDB as they cross the network, thus providing an external description of the edge-to-edge quality of service that can be expected by packets of that PDB within that network. A PDB is formed at the edge of a network by selecting certain packets through use of classifiers and by imposing rules on those packets via traffic conditioners.

The description of a PDB contains the specific edge rules and PHB type(s) and configurations that should be used in order to achieve specified externally visible characteristics.

In addition to defining a format for PDB descriptions, specific descriptions of PDBs that can be constructed using the standard PHBs will be developed and reviewed by a design team prior to informational or standards track publication.

The group will continue to analyze related security threats, especially theft of service or denial of service attacks, and suggest counter-measures.

The group will not work on:

o mechanisms for the identification of individual traffic flows

o new signalling mechanisms to support the marking of packets

o end to end service definitions

o service level agreements

Goals and Milestones:
Done   Publish draft of format for BA descriptions
Done   Meet at Adelaide IETF to review tunnels draft, discuss initial PDB descriptions
Done   Solicit PDB descriptions
Done   Finalize tunnels draft, submit to IESG
Done   Finalize PDB format draft, submit to IESG
Done   Meet at Pittsburgh IETF
Done   Meet at San Diego IETF
Sep 01   Finalize model, MIB and PIB drafts, submit to IESG
Sep 01   Submit Informational terminology updates to IESG
Request For Comments:
RFC2474PSDefinition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers
RFC2475 An Architecture for Differentiated Services
RFC2598PSAn Expedited Forwarding PHB
RFC2597PSAssured Forwarding PHB Group
RFC2983 Differentiated Services and Tunnels
RFC3086 Definition of Differentiated Services Per Domain Behaviors and Rules for their Specification
RFC3140PSPer Hop Behavior Identification Codes

Current Meeting Report

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