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- Introduction to TCP/IP 9
- TCP/IP Protocol Layering Concepts 43
- Network Support for TCP/IP 83
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Computer networks have come to play an increasingly impor
tant role in the lives of people. The motivation for the
widespread use of computer networks is the need for
people with common and shared interests to communicate with each
other. People who are a part of a business organization need to
communicate and share information with each other. Because information can
more easily be represented and manipulated in electronic form, the
employees of the business organization have access to terminals attached
to mainframes/minicomputers, personal computers, or
computer workstations. To meet the need to share and communicate
information, the computers need to be connected. When computers
are connected to each other, a data communication network—the
computer network—is created.
Within a business organization at a single location, the
computer network is usually a local area network (LAN). When the
business organization needs to communicate with other businesses or
individuals at a different location, a wide area network (WAN) is created
to connect the different sites together (see fig. 1.1).
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Figure 1.1 Local area and wide area computer networks.
The example that has been given is of a business organization. However,
today's networks have grown to encompass people from different backgrounds and
organizations, as can be seen in the phenomenal growth of the Internet, the
world-wide network that links private individuals, business organizations, nonprofit
organizations, governments, international organizations, and educational institutions. Also,
it is not necessary that the users of computer network be people; the users can
be devices performing a certain controlling function. For example, in the case of
an aircraft, ship, or automobile, several computers may be monitoring different
aspects of the control systems that need to communicate control information.
This book focuses its attention on computer networks that have been built with
a networking technology lumped under the name TCP/IP, which stands for
Transmission Control Protocol/Internet Protocol. Networks that use this technology are
called TCP/IP networks.
This technology plays a major part in the world-wide Internet and many
business networks. Perhaps one reason for the appeal of TCP/IP networks is that they
are based on an open specification that is not controlled by any vendor.
This chapter examines the origins of TCP/IP networks and the commercial uses
of this protocol. It also gives a brief overview of the more common application
services
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that use the TCP/IP protocol. This chapter is very conceptual in nature and
offers you a more general, introductory look at the technology. Upcoming chapters
deal more specifically with how TCP/IP literally works.
Before examining the details of TCP/IP networks in later chapters, an overview
of TCP/IP would be helpful in giving you a more general perspective of
`TCP/IP networks. To assist you in understanding TCP/IP networks, the following sections
will give you a clear definition as well as the history that led to the commercial uses
of TCP/IP.
When people use the acronym TCP/IP, it can refer to a number of different
concepts and ideas. The most popular use of the term TCP/IP is
a communications protocol for data transport. The TCP stands for Transmission Control Protocol and IP stands
for Internet Protocol.
What is a communications protocol? A communications
protocol is a set of rules and regulations by which computers networked together can communicate. Just as
people require the use of a commonly understood language to communicate, so do
computers. If people are talking to each other in a room, chances are very high that they
are speaking in a common language. In a room full of diplomats from different
countries, such as in the United Nations, you can expect different languages to be
spoken. But in this case, you can also expect to find translators who can help the
people understand each other. Computer networks mimic the communications
methods used by human beings. This situation is not exactly a coincidence because
computer networks are designed by human beings. A very common and popular language
used in computer networks is the TCP/IP protocol. If other protocol languages are to
be used in the computer network, you need translator computer devices, which
can translate to a common language.
The term TCP/IP is not limited just to the Transmission Control Protocol (TCP)
and the Internet Protocol (IP). The term can also refer to a group of protocols—such
as the User Datagram Protocol (UDP), File Transfer Protocol (FTP), Terminal
Emulation Protocol (Telnet), Hypertext Transfer Protocol (HTTP), and so on—that
are associated with TCP/IP.
Figure 1.2 shows a sample TCP/IP network that uses TCP/IP. In this figure,
TCP/IP refers to the communications protocol and the applications—such as FTP,
Telnet, HTTP—that use TCP/IP.
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Figure 1.2 Example TCP/IP internet.
Networks that use TCP/IP are called TCP/IP
internets. Figure 2.1 is an example of a TCP/IP internet.
A distinction must be made between a TCP/IP internet and the Internet. A TCP/IP internet is any network that uses TCP/IP protocols that may
or may not be connected to other networks. The Internet is currently the largest
network in the world with thousands of computers. It spans several continents and is
predominantly based on TCP/IP.
When businesses use Internet services—particularly the World Wide Web
service implemented by the HTTP protocol—on their own private network, the TCP/IP
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internet is called an intranet. Application services used on intranets are either
the same as those used on the Internet or are modified versions of the Internet
application programs.
The discussion of the TCP/IP technology in this book covers internets, intranets,
and the global Internet.
In the late 1960s, DARPA (Defense Advanced Research Projects Agency) of
the United States noticed that there was a rapid proliferation of computers in
military communications. Computers, because they could be easily programmed,
provided flexibility in achieving network functions that was not available with other types
of communications equipment. The computers that were used in military
communications were manufactured by different vendors and were designed to interoperate
with computers from that vendor only. Vendors used proprietary protocols in
their communications equipment. The military had a multivendor network but no
common protocol to support the heterogeneous equipment from different vendors.
To solve these problems, the U.S. Department of Defense (DoD) mandated that
the Defense Advanced Research Projects Agency (DARPA) define a common set
of protocols. The reasons for having a common set of protocols include the following:
- Procurement simplification. By mandating a common set of protocols, it
is possible for the military to have a Request for Proposal, which specifies
that communications products use the common protocol.
- Fostering of competition among
vendors. Vendors can compete with each other based on the merits of their implementation of a standard
protocol. If a common set of protocols is not required, vendors can implement
their proprietary protocols against which other vendors cannot compete.
- Interoperability. By having vendors use a common set of
protocols, interoperability between equipment from different vendors becomes a reality.
If this equipment does not interoperate, the problem is probably due to a
difference in implementation. The vendors can then refer to the standard
specification of the protocol to isolate the problem.
- Vendor productivity and efficiency. Vendors can focus their attention
on a single protocol rather than spread their efforts trying to implement
several protocols. This condition makes the vendors' efforts more productive.
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