A HYBRID RANDOM/CONTROLLED ACCESS LAW FOR REAL-TIME APPLICATIONS

Abstract

LANS have opened up vistas for interconnecting various data communication equipment and providing shared access to expensive resources like printers,disk storage etc. The existing LAN protocols like CSMA/CD and Token Passing don't exhibit uniform delay and throughput characteristics over all ranges of message loads. CSMA/CD performs better than Token Passing scheme at low loads where as Token Passing outclasses CSMA/CD at high loads. Various Hybrid Protocols, which combine the features of both CSMA/CD and Token Passing have been proposed to address this problem. Of late there has been extensive research in the field of Real-Time Communications. Protocols have been designed to support Time-Constrained traffic. This dissertation work is an attempt to implement a Hybrid Protocol which exhibitsthe features of CSMA/CD at low message loads and Token Bus at high loads. To support Real-Time constraints a Time Window has been added such that the message with the minimum latest time to send will be considered first for transmission at each node. The most important performance criterion in Real-Time Communication is the Message Loss. The Percentage of Message Loss and Channel Utilization are computed for different values of Time Window. Such a network was implemented on IBM compatible PCs and message deadlines were assigned by a random number generator. The results have been discussed.