DATA COMMUNICATION PRINCIPLES Data Link Control Layer Protocol

DATA COMMUNICATION PRINCIPLES : Data Link Control Layer Protocol Examples

Data Link Control Layer Protocol Examples We discussed the functions to be provided by a data link control layer. Also discussed were some of the procedures and mechanisms used to implement those functions. We learnt that synchronization could be implemented on a block-by-block basis (synchronous transmission) or character-by-character basis (asynchronous transmission). Different address requirements for each station were discussed. The bulk of the discussion was on flow and error control mechanisms. We continue with the discussion of DLC layer in this chapter taking examples of some data link control layer standards. The OSI seven-layer model has a protocol defined at the DLC layer called HDLC (High-level Data Link Control) protocol. We will start out with HDLC and discuss its functions and how they are performed. Following HDLC, we will look at the layer 2 protocol for broadband ISDN, the Asynchronous Transfer Mode (ATM). We will close the DLC examples with a discussion on the medium access control (MAC) sublayer of the IEEE WLAN.

The HDLC is defined as International Standardization Organization’s recommendations ISO 3309 and ISO 4335. It has captured the imagination of much of the world of data communications. It provides a variety of options that the two stations may be able to negotiate before data exchange. The ATM protocol is a natural evolution of the availability of high-speed physical layer in the form of optical network standard, called SONET (Synchronous Optical Network) in the USA and SDH (Synchronous Digital Hierarchy) by ITU. It is well known that constant size and smaller packets would result in relatively less queueing delay. Using these and other results, the networking community all across the world came up with the concept of using a DLC layer above SONET/SDH that would consist of short (53 octet) packets, called cells. In discussion on WLAN, we restrict our focus on the medium access control sublayer. The wireless LANs, besides their unique applicability, provides an interesting case of a medium access control (MAC) sublayer.

REFERENCES • Ahmad A. - Data Communication Principles. For Fixed and Wireless Networks • Cornelius T. Leondes - Database and Data Communication Network Systems, Three-Volume Set_. . -Academic Press