88 Part I • Information Technology
communication channel. Electrical engineers work at this
level, with typical design issues involving such questions as
how many volts should be used to represent a 1 and how
many for a 0.
Hopefully this brief description of the seven layers
conveys the general role of each layer. Perhaps the easiest
way to think about this entire process is that the original
communication goes through a multilevel translation
process (which is really much more than translation) in a
device/system independent way that is totally transparent
to the user.
TCP/IP Transmission Control Protocol/Internet
Protocol (TCP/IP)is not part of the OSI reference model,
although it roughly corresponds to the network and
transport layers. TCP/IP is used in many non-Internet
networks, including Internet2, as well as in the UNIX and
Linux operating systems and in Microsoft Windows. Most
important, TCP/IP is the protocol used on the worldwide
Internet and on numerous intranets operating within
organizations. TCP/IP, not OSI, has become the de facto
standard protocol for networking around the world.
Nevertheless, TCP/IP is only a partial set of protocols, not
a fully developed model. Thus, computer scientists and
other computer professionals have, in effect, developed an
extended TCP/IP model. First, we will consider the
TCP/IP protocols themselves, and then we will turn to the
extended TCP/IP model.
The IP portion of the TCP/IP protocol corresponds
roughly to the network layer of the seven-layer OSI model,
while the TCP portion corresponds approximately to the
transport layer. TCP/IP accepts messages of any length,
breaks them into pieces less than 64,000 bytes, sends the
pieces to the designated receiver, and makes sure that the
pieces are correctly delivered and placed in the right order
(because they might arrive out of sequence). TCP/IP does
not know the path the pieces will take and assumes that
communication will be unreliable. Thus, substantial error-
checking capabilities are built into TCP/IP itself to ensure
reliability.
The original Internet developers envisioned the
complete networking protocol as having four layers—the
networking and transport layers as the middle layers, with
a hardware layer below these two layers and an application
layer above them (Dennis, 2003, p. 14). From a practical
standpoint, this four-layer view of the world is not too
different from the OSI model: The OSI presentation and
session layers are often not used, and the data link and
physical layers of the OSI model are both incorporated in
the four-layer model’s hardware layer. In this extended
TCP/IP model, the application layer includes protocols
such as SMTP (for e-mail), HTTP (for Web pages), and
FTP (for file transfer). The transport layer is TCP, of
course, and the network layer is IP. Then the hardware
layer includes the various LAN standards, ISDN, SONET,
and DSL, among others. This extended TCP/IP model
represents reality in terms of the standard set of networking
protocols in the early twenty-first century.
We now have all the pieces of the network puzzle.
Network protocols provide the means by which various
elements of telecommunications networks can communi-
cate with one another. Thus, networks consist of physical
media (or wireless), arranged according to some topology,
in a particular type of network, with communication
throughout the network permitted through the use of
particular protocols.The Exploding Role of Telecommunications and Networking
We have already stressed the critical role of telecommuni-
cations and networking several times, but to make the
point even stronger, we will discuss how the role of
telecommunications and networking is exploding in
organizations today. In fact, many authorities suggest that
the network (not the computer) is the most critical and
most important information technology of the future. To
illustrate this explosion, we will consider four areas of
operation in which telecommunications networks are of
critical and growing importance.Online Operations
The dominant activities of many organizations have now
been placed online to the computer via a network. For
banks and other financial institutions, teller stations
(as well as automated teller machines) are all online.
Tellers directly update your account when you cash a
check or make a deposit. The bank does not care what
branch in what city you use because your account is
always up-to-date. Not quite as obviously, insurance
companies have most of their home office and branch
office activities online. When an insurance claim is made
or paid, when a premium is paid, or when a change is made
to a policy, those activities are entered online to the
insurance company network. These and other financial
institutions (e.g., brokerage firms) simply could not operate
as they do without telecommunications networks.
The computerized reservations systems of the major
airlines are another example of an indispensable use of
online systems. In fact, computerized reservation systems
constitute the core marketing strategy of the major airlines.
These reservation systems were originally designed to be