A general approach to real-time message scheduling over distributed broadcast channels

We introduce a class of real-time scheduling problems as they arise in distributed multiaccess broadcast communication channels. This class of problems is more general, hence more realistic, than the problems considered when assuming periodic or sporadic releases of messages. The authors examine the most popular algorithms and protocols, such as STDMA, polling and bus/ring token-passing. Contrary to widespread belief, the authors demonstrate that they cannot solve the class of real-time problems they are interested in. Adversary arguments are used for this purpose. The class of pure on-line distributed deadline-driven non-preemptive contention detection-and-resolution algorithms, referred to as D-NP-EDF/CDR, is shown to dominate any other class of algorithms for the problems considered. Consequently, optimal algorithms for the authors' problems can only belong to this class. The authors then show how to establish the desired timeliness properties as well as feasibility conditions for algorithms in the class D-NP-EDF/CDR.