Schemesfor Hard Real - Time Communications

We study version selection schemes for hard real-time communications in multi-access networks. In many hard real-time systems a message may have several versions, e.g., a long version and a short version. The long version of a message contains complete information and is the preferred version to be transmitted. The short version contains less information and requires less time to be transmitted. Version selection schemes are responsible for determining which version of a message to transmit, and must make a tradeoo between information completeness and message loss. Two classes of version selection schemes are proposed in this paper: those that are based on message time constraints, and those that are based on the network traac. We discuss the design and implementation of both classes of version selection schemes used in conjunction with a window based media access protocol. The simulation results show that as the network load increases, our version selection schemes are effective at reducing the message loss by trading oo the proportion of long version messages sent.