Prioritizing packet transmission in local multiaccess networks

Abstract

Carrier sense multiple access with collision detection (CSMA/CD) protocols have been extensively studied and developed for local area networks. In CSMA/CD protocols, all messages are treated equally in competing for the communication channel. Thus, important or time-critical messages may be severely delayed. In this paper, a new CSMA/CD protocol with message-based priority functions is proposed. A priority code comparison period is needed to determine the highest priority class that can compete for the comunication channel. A contention period based on CSMA/CD scheme is then followed. Both nonpreemptive discipline and preemptive discipline are discussed. In each discipline, both the single mode and the batch mode are considered and compared. The overhead in implementing the proposed protocol, either for a few or for a large number of priority classes, is shown to be minimal. In general, a preemptive single mode scheme provides a better performance. The requirements of hierarchical independence of performance and fairness are satisfied.