The rules that de?¬?ne how systems talk to one another are called
protocols.
Many internetworking protocols can be used to establish communications paths between
systems, and each of these protocols provides very similar functions. To provide a way to
establish some common and open rules for building a data communications protocol, the
International Organization for Standardization (ISO) created the OSI reference model.
The following sections describe the purpose of the OSI reference model and the TCP/IP
protocol stack. You also learn how the OSI reference model facilitates data communication.
OSI Reference Model
The OSI reference model is the primary model for network communications. The early
development of LANs, MANs, and WANs was chaotic in many ways. The early 1980s saw
tremendous increases in the number and sizes of networks. As companies realized that they
could save money and gain productivity by using networking technology, they added
networks and expanded existing networks as rapidly as new network technologies and
products were introduced.
By the mid-1980s, companies began to experience dif?¬?culties from all the expansions they
had made. It became more dif?¬?cult for networks using different speci?¬?cations and
implementations to communicate with each other.
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