Managing Information Technology

86 Part I • Information Technology

Application

Layer

Presentation

Layer

Session

Layer

Transport

Layer

Network

Layer

Data Link

Layer

Physical

Layer

FIGURE 3.11 Seven Layers of the OSI Reference Model

designed and built the network, and the Indiana University
Global Network Operations Center, who manages the
network.
The Internet2 network is a backbone network used
by the Internet2 universities—it provides an effective
interconnection among regional networks that have been
formed by the Internet2 universities. Connections from
these regional networks and the commercial Internet can
occur at any of the locations labeled on the map. The
Internet2 network is essentially a ring topology, but it has
been enhanced with Salt Lake City–Sunnyvale, Denver–El
Paso, Kansas City–Houston, Chicago–Atlanta, and
Cleveland–Washington, D.C., cross-ring links. The
Internet2 network and the other Internet2 projects are the
precursors of tomorrow’s Internet.

Network Protocols

There is only one more major piece to our network puzzle.
How do the various elements of these networks actually
communicate with one another? The answer is by means
of a network protocol, an agreed-upon set of rules or
conventions governing communication among elements of
a network, or, to be more precise, among layers or levels of
a network. In order for two network elements to communi-
cate with one another, they must both use the same proto-
col. Therefore, the protocol truly enables elements of the
network to communicate with one another.
Without actually using the protocol label, we have
already encountered several protocols. LANs, for example,
have four widely accepted protocols: contention bus, token
bus, token ring, and wireless. Historically, the biggest
problem with protocols is that there have been too many of
them (or, to look at the problem in another way, not enough
acceptance of a few of them). For example, IBM and each
of the other major hardware vendors created their own sets
of protocols. IBM’s set of protocols is collectively termed
Systems Network Architecture (SNA). IBM equipment
and equipment from another vendor, say, Hewlett-Packard,
cannot communicate with each other unless bothemploy
the same protocols—IBM’s, or HP’s, or perhaps another
set of “open-systems” protocols. The big challenge
involved in integrating computers and other related equip-
ment from many vendors into a network is standardization
so that all use the same protocols.
In the past three decades, considerable progress has
been made in standardization and acceptance of a set of
protocols—although we are not ending up where most
commentators would have predicted in the late 1980s. At
that time, it appeared that the Open Systems
Interconnection (OSI) Reference Model, developed by
the International Organization for Standardization (ISO),

would become the standard set of protocols. The OSI

model defines seven layers (see Figure 3.11), each of

which will have its own protocol (or protocols). The OSI

model is only a skeleton, with standard protocols in

existence for some layers (the four LAN protocols are part

of the data link layer), but with only rough ideas in other

layers. All major computer and telecommunications

vendors—including IBM—announced their support for

the OSI model, and it appeared that OSI was on its way.

For better or worse, the movement toward the OSI

model was essentially stopped in the 1990s by the

explosion of the role of the Internet and the creation of

numerous intranets within major organizations. Both the

Internet and intranets employ Transmission Control

Protocol/Internet Protocol (TCP/IP) as their protocol.

TCP/IP is not part of the OSI reference model, and it is a

less comprehensive set of protocols than OSI, correspond-

ingly roughly to two of the seven OSI layers. Both the OSI

model and TCP/IP are important, for different reasons, so

we will explore both sets of protocols. The OSI model

provides an extremely useful framework for considering