Interaction between protocol levels in a prioritized CMSA broadcast network

Abstract

The high communication bandwidths and low propagation delays available to local area networks have motivated multiplexing techniques that are significantly different from those utilized in geographically distributed networks. In recent years, several local networks have successfully multiplexed a broadcast medium for communication among multiple digital systems. The Hyperchannel product of the Network Systems Corporation is the most ambitious of these networks yet attempted. Discrete event simulation studies of the Hyperchannel demonstrate surprising performance variations resulting from rather subtle protocol, timing, and topology changes. Early analytic and simulation studied showed the effectiveness of the lowest level Hyperchannel contention mechanisms. Later simulations, including the next level of microcoded error and flow control protocols, showed that great care must be taken to maintain high trunk utilization through both protocol levels. Examples of performance degradation arising from interaction between the two protocol levels illustrate the type of information that can be obtained from simulation analysis of communication systems too complex for current state of the art mathematical models.