Implementing Priority Functions in Local Area Networks
Prioritizing the handling of various data and control messages is important for network performance. Among the three most popular media access protocols that are likely to be standardized, CSMA/CD protocol is the only one that does not provide priority mechanism in handling various priority levels of packets. 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. A new CSMA/CD protocol implemented with message-based priority functions is proposed. In this scheme, a distributed priority-code comparison algorithm is developed to determine the highest priority class that can compete for the communication channel. Both nonpreemptive and preemptive disciplines are discussed. In each discipline, both the single mode and the batch mode are considered and compared. The overhead in implementing the proposed protocol has shown, through simulation, to be much less than previously proposed methods. Among four different operating alternatives, the preemptive single mode scheme, in general, provides a better performance.
KeywordsBatch Mode Priority Level Priority Class Transmission Period Priority Function
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