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often simpler than its physical deployment. Knowledge of the communication
models is important, but it can be confusing. To minimize this confusion, the
OSI-RM will be the default reference model in discussing the protocols and their
respective layer of operation.
The goal of this chapter is to describe the various protocols of the TCP/IP protocol
suite. Using the OSI-RM model, the key elements of TCP/IP are covered: what each
protocol does, its sequence in the suite, and services it needs to perform. This
chapter also explores how the various protocols of the TCP/IP suite work together
and how TCP/IP relates to other transport mechanisms (such as Ethernet and FDDI)
that carry TCP/IP packets. An understanding of the material is crucial to anyone who
is building or managing a TCP/IP based computer network.
The Origins of TCP/IP
TCP/IP gets its name from the most widely used protocols in the suite: Transmission
Control Protocol (TCP), the OSI-RM Level 4 protocol that provides connectionoriented
data transport service, and Internet Protocol (IP), the OSI-RM Level 3
protocol that provides datagram delivery and addressing facilities. Early in TCP/IP's
development, its capability to provide network connectivity between different types
of hosts was extolled as one of its greatest virtues.
This virtue has made TCP/IP the protocol on which most client/server computing is
based. Most interactive application layer protocols use the client/server model to
exchange data. Client/server is a transaction-based processing model. The client
represents the user or device making a data request. This request is made using a
common data exchange process or user interface to a server.
The server processes client requests by providing data that can be processed by the
requesting client. Both the server and the client agree on the data exchange process
before transactions are made. This is ensured because both the client and server are
following a common application programming interface (API) that specifies how the
transaction function calls will take place.
The capability of TCP/IP to function equally well across both WAN and LAN
connections, coupled with its diverse computer platform support, makes TCP/IP the
natural choice for connectivity in heterogeneous internetworking environments.
Although TCP/IP is vendor-independent and in the public domain, it has required
continuous development as computer and networking technologies have
progressed. This development is overseen by the Internet Engineering Task Force
(IETF), which consists of more than 80 sub-committees that develop, review and
revise the technologies standards used on the Internet. The IETF operates under the