Channel characteristics in local-area hard real-time systems

Abstract

In many distributed hard real-time systems, i.e., systems in which tasks have deadlines, it is essential that messages between nodes be delivered in a timely manner. If the nodes are connected by a local area network, the channel access protocol should provide for message delivery within bounded time. Real-time systems can then be designed assuming bounded message delivery delays. Recently a number of protocols have been proposed for bounding channel access delays. But the bound mainly applies to the message that is in front of a node's queue of messages waiting to be transmitted. This paper concerns the computation of maximum channel access delay for any message generated by a node. This computation utilizes one of the above mentioned protocols. Additionally, it uses the specification of the system; in particular, the specification of the periods, execution times, and bounded message generation rates of the tasks as well as the channel bandwidth. The scheme presented here can also be used to compute the channel bandwidth needed to guarantee that every message generated by the specified tasks will be transmitted within a specified bounded time.