DATA COMMUNICATION Principles Error Control Procedures Error Control

DATA COMMUNICATION Principles : Error Control Procedures

Error Control Procedures In Chapter 5, we learnt that there are potentially two error control mechanisms, forward error control (FEC) and backward error control (BEC). In FEC, errorcorrecting codes are used that have the capability of correcting a specified number of errors. In BEC, the receiver has the capability of only detecting the errors, but not correcting them. The transmitter keeps a copy of the unacknowledged packets. If a retransmission request is received from the receiver, the copy is retransmitted. The stored copy of the packet is discarded on receipt of an acknowledgement.

There are two types of performance related issues in error control. First issue to study is the effect of error control mechanism versus no error control mechanism. Second important issue is the overhead due to error control. In the study of error control procedures (Chapter 5), we have demonstrated how an error control procedure as simple as adding a single parity bit improves that chances of a packet with errors to be detected. In fact, in coding theory the term coding gain is used to compare the benefits of various codes. The coding gain is related to the amount of signal power saved due to avoiding errors as a result of coding. In this chapter, we concentrate on cost of error control. Each added bit for error control is an overhead bit and utilizes a part of the link capacity. Each retransmission also utilizes the link capacity.

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