Data Link Protocol
In the preceding chapter the mechanical and electrical, i.e., physical, interface between DTE and DCE was considered, but such an interface alone is usually insufficient to handle conventional digital telecommunications between remotely located terminals. The reason is that the physical level, along with the accompanying modem, only passes bits blindly without any regard for what the bits mean or how they are grouped together. There is no indication, for example, as to where characters and data fields begin and end unless some convention is agreed on beforehand between the users of the physical link. Clearly, it is desirable to have a well-defined set of rules for communicating over point-to-point links that can be used by a wide range of different terminal users. In general, such a formal set of rules is called a protocol, and so the set of rules for link operation is a data link protocol.
KeywordsControl Field Cyclic Redundancy Check Secondary Station Error Check Control Frame
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