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