TCP/IP (Transmission Control Protocol/Internet Protocol) is a suite of network protocols, developed by the Defense Advance Research Projects Agency (DARPA) to connect a number different networks designed by different vendors into a network of networks (the "Internet").

TCP and IP are only two of the protocols within this suite; they are however, two of the most important. A protocol specification is comparable to a language. As with any spoke language, there are rules regarding the meaning of certain sounds, and which words signal the beginning or ending of a conversation. You can imagine the scenario of a Greek man, who can only speak Greek, communicating with a French speaking person, who only speaks French. They simply cannot exchange information effectively. However, if they both can speak a common language, Say English, they would communicate perfectly.
TCP/IP is a set of rules that can be considered computer language. This means that, it will be virtually impossible for a computer which runs with the TCP/IP stack of protocols; to exchange information with one that speaks, say, only Novell's IPX. However, with TCP/IP enabled, computers using dissimilar operating systems are able to exchange information in an orderly fashion.

In practice, a communications network will sustain damage, so the DOD designed TCP/IP to be robust and automatically recover from any node or phone line failure. This design allows the construction of very large networks with less central management. However, because of the automatic recovery, network problems can go undiagnosed and uncorrected for long periods of time.

The most commonly used most commonly quoted model for describing data communications is the open systems Interconnection (OSI) model. This seven layer model was designed for OSI set of protocols and gives us a framework for examining the roles and responsibilities of each protocol within the TCP/IP suite. The following gives a brief definition of the OSI model and then compares it to the Department of Defence four-layer data communications model that originally was used to classify protocols within the TCP/IP protocol suite.