A protocol is best defined as a set of rules. In digital communications, protocols determine where certain information will be found in the binary bit stream. Addresses, control information, user data, and various other fields must be clearly defined and consistent within each transmission. This is the job of the protocol.

Not all protocols are alike. Many protocols provide similiar features, but are all very different both in format and in implementation. Here, we will outline the common features of a protocol and then look at a model used in developing protocols even today.

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Copied with permission,McGraw-Hill Telecommunications from the book Telecommunications Protocols, by Travis Russell, 1997 McGraw-Hill Telecommunications, pages 29-35.