Differentiated Services (diffserv)

Last Modified: 2003-03-11


Transport Area Director(s):

Transport Area Advisor:

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General Discussion: diffserv@ietf.org
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Archive: ftp.ietf.org/ietf-mail-archive/diffserv/

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

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

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
Done    Submit Informational terminology updates to IESG
Done    Finalize model, MIB and PIB drafts, submit to IESG

No Current Internet-Drafts

Request For Comments:

Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers (RFC 2474) (50576 bytes) obsoletes RFC 1349,RFC 1455/ updates RFC 1122,RFC 1123,RFC 1812/ updated by RFC 3168
An Architecture for Differentiated Services (RFC 2475) (94788 bytes)
An Expedited Forwarding PHB (RFC 2598) (23656 bytes) obsoleted by RFC 3246
Assured Forwarding PHB Group (RFC 2597) (24068 bytes) updated by RFC 3260
Per Hop Behavior Identification Codes (RFC 2836) (13399 bytes) obsoleted by RFC 3140
Differentiated Services and Tunnels (RFC 2983) (35644 bytes)
Definition of Differentiated Services Per Domain Behaviors and Rules for their Specification (RFC 3086) (63122 bytes)
Per Hop Behavior Identification Codes (RFC 3140) (16586 bytes) obsoletes RFC 2836
An Expedited Forwarding PHB (RFC 3246) (33896 bytes) obsoletes RFC 2598
Supplemental Information for the New Definition of the EF PHB (RFC 3247) (53786 bytes)
A Delay Bound alternative revision of RFC2598 (RFC 3248) (21597 bytes)
New Terminology and Clarification for Diffserv (RFC 3260) (21900 bytes) updates RFC 2597
Management Information Base for the Differentiated Services Architecture (RFC 3289) (239041 bytes)
An Informal Management Model for Diffserv Routers (RFC 3290) (129443 bytes)
Differentiated Services Quality of Service Policy Information Base (RFC 3317) (188553 bytes)