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322 STANDARDS ANDPROTOCOLS INDATACOMMUNICATIONShowever, most are of a serious nature so that the sys-
tem exists to this day. Of special interest here are those
RFCs concerned with standards and codes of practice.
The standards process begins with a specification, which
undergoes several review phases within the Internet com-
munity. These reviews are usually conducted via mailing
lists. Each version of the specification is published as an
RFC. When the specification becomes a standard it keeps
the same RFC but additionally has a label of the form
STDxxx. A similar process applies to codes of practice
where the label is BCPxxx (best current practice). Each
standard must pass through a set of three maturity lev-
els known as the “standards track.” They begin life as a
“proposed standard,” at which level it is assumed they
have no known problems or omissions. The second stage
requires the specification to have two implementations
from two different code bases. Once sufficient successful
operational experience has been gained, the level is raised
to that of “Internet standard.”
Once approved, the RFC editor is informed and it is the
editor’s responsibility to ensure publication and currency.The World Wide Web Consortium (W3C)
The World Wide Web is without doubt the most popular
application ever to be placed upon the Internet. It consists
of multitudes of files scattered across the globe on millions
of computers. The Web began life at the European Particle
Physics laboratory in 1989 when Tim Berners-Lee wished
to exchange data with fellow scientists (Berners-Lee
et al., 1994). In 1994 he made agreements between MIT
and CERN to develop the Web with support from the Eu-
ropean Commission and DARPA. The W3C collects ideas
from around the world to form a view of future directions
for the WWW. It then designs appropriate Web technolo-
gies and contributes to standardization through specifi-
cations (recommendations). All of this is offered freely
as part of the WC3 stated philosophy. This raises ethi-
cal questions when companies attempt to commercialize
areas of the Web or its infrastructure. W3C has over 30
working groups working on what it terms as “activities.”
Their results form the basis for recommendations, some
of which are PNG (1996), CSS (1996), XML (1998), DOM
(1998), SVG (2001), XHTML (2001), and XML-Signature
(2002). For a complete list the reader is referred to the
W3C Web site (W3C, 2002).ATM Forum
Although standards for ATM have been in place since 1984
under the auspices of the ITU-T it was not until 1991 that
the ATM forum was established to promote this broad-
band technology as the packet-switching technology for
high-speed data exchange. (ATM is particularly suited to
multimedia applications because it allows different data
rate streams to operate concurrently.) Like so many of
its counterparts the Forum is an international voluntary
organization that makes “recommendations.”International Telecommunication
Union (ITU)
The ITU is the world’s oldest international organization,
being first established on 17th May 1865 to manage theearly international telegraph networks in Europe. Initially
there were 20 European founding states in the Interna-
tional Telegraph Union (ITU); its current name came into
effect on 1 January 1934. In 1947 under an agreement with
the United Nations, it became a UN specialized agency
with headquarters in Geneva. In 1992 the organization
was divided into three sectors: Telecommunication Stan-
dardization (ITU-T), Radiocommunication (ITU-R), and
Telecommunication Development (ITU-D).
The work relevant to the Internet is carried out by study
groups that develop new and revised ITU-T recommenda-
tions. The ITU-T currently produces some 210 of these
recommendations each year.Commit ́ee Consultatif International
T ́el ́ ephonique et T ́el ́ egraphique (CCITT)
The CCITT was a separate organization that set interna-
tional communications standards; it is now part of the
ITU. Amongst its more well-known standards are those
for fax transmissions, e.g., Group 3 and Group 4, and
the V series for communication at lower modem speeds.
With respect to the Internet, the CCITT provided X.25, a
packet-switching protocol for WANs; X.400, the protocol
for e-mail; X.500, an extension to X.400 that defines ad-
dressing formats so that e-mail systems can be linked up;
and the I xxx series for user interfaces.INTERNETWORKING MODELS
AND LAYERING PROTOCOLS
Standards are necessary to provide interoperability be-
tween two network-connected hosts. For this to occur,
both hosts must agree on their approach to issues such
as call establishment, error correction, and data transfer.
This agreement then forms a set of rules that defines a
protocol that each peer layer must follow. These rules are
formalized as standards, and in order to provide a com-
mon framework for these standards a reference model
is defined. This section examines the common reference
models.OSI (7-Layer) and TCP/IP Models
The most widely known reference model is that of the
Open Systems Interconnections (OSI), referred to com-
monly as the 7-layer model. It is most often compared
directly to the transmission control protocol/Internet pro-
tocol (TCP/IP) model and we shall follow the same pattern
in this section. For any model the concept of a service
provider and receiver is used. Each standard divides the
reference model into a number of layers, each of which
acts as a service receiver or provider, depending upon the
logical state it is in. The OSI reference model was pro-
duced by an ISO working group and is occasionally re-
ferred to as the ISO model. It is the generic model for all
networked systems although other protocol standards use
a different number of layers.
In the OSI 7-layer model the following layers are
present: physical layer, data link layer, network layer,
transport layer, session layer, presentation layer, and the
application layer. It is common practice to use the num-
bers associated with these layers rather than their names;