Services and protocols of the data link layer

Data Link control protocols are among the oldest recognized communication protocols. The protocol provides a well-defined set of rules which govern the interchange of supervisory information and user data over the interconnecting communication link. Such rules are essential to successful and efficient operation. Data Link protocols have evolved continuously from the early free-wheeling protocols, through the widely implemented character-oriented protocols, to the increasingly popular bit-oriented protocols. Data Link protocols play a vital role in the drive toward Open Systems Interconnection (OSI). Constituting Layer 2 of the International Standards Organization (ISO) Reference Model, these procedure and the services that they offer, are directed at assuring successful and reliable transfer of information over point-to-point or multipoint data links. This paper reviews the role of link protocols in the open systems environment. It discusses the objectives and functions of these protocols and delineates the services provided to the higher layers. A review, with examples, of the protocols suitable for use within the framework of OSI is included. The paper concludes with a look at some of the current Data Link issues.