Differentiated Services (diffserv)

Note: The data for concluded WGs is occasionally incorrect.

Final Charter for 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


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


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

Done milestones

Date Milestone Associated documents
Done Finalize model, MIB and PIB drafts, submit to IESG
Done Submit Informational terminology updates to IESG
Done Meet at San Diego IETF
Done Meet at Pittsburgh IETF
Done Finalize PDB format draft, submit to IESG
Done Finalize tunnels draft, submit to IESG
Done Meet at Adelaide IETF to review tunnels draft, discuss initial PDB descriptions
Done Solicit PDB descriptions
Done Publish draft of format for BA descriptions