The Best-Effort Virtual-Time CSMA/CD Protocols for Real-Time Systems

Two clairvoyant virtual-time CSMA/CD protocols for dealing with time-constrained messages are described. A clairvoyant protocol takes into account not only the messages currently available for transmission but also the messages expected to be produced in the future. In the absence of clairvoyancy, the urgent but currently unavailable messages may not be successfully transmitted when they are actually produced. Simulation results show that these two clairvoyant protocols yield better performance over two other virtual-time protocols with no clairvoyancy within a reasonable range of system loads. The percentage of message timing failures is used as the primary performance measure. Keywords: Real-Time. Communication Protocols. Clairvoyancy. Timing failures. Contents 1 Introduction 1 1.1 Task and Message Characteristics : : : : : : : : : : : : : : : : : : : : 2 1.2 Real-Time Protocols Review : : : : : : : : : : : : : : : : : : : : : : : 3 1.3 Real-Time Protocols: Clairvoyancy : : : : : :..