Early Detection of Message Forwarding Faults
Abstract and Figures
In most communication networks, pairs of processors communicate by sending messages over a path connecting them. We present communication e cient protocols that quickly detect and locate any failure along the path. Whenever there is excessive delay inforwarding messages along the path, the protocols detect a failure (even when the delay is caused by maliciously-programmed processors). The protocols ensure optimal time for either message delivery or failure detection. We observe that the actual delivery time of a message over a link is usually much smaller than the apriori known upper bound D on that delivery time. The main contribution of the paper is the way tomodelandtakeadvantage of this observation. We introduce the notion of asynchronously early determinating protocols, as well as protocols that are asynchronously early terminating, i.e., time optimal in both worse case and typical cases. More precisely, we present a time complexity measure according to which one evaluates protocols both in terms of D and.Weobserve that asynchronously early termination is a form of competitiveness. The protocols presented here are asynchorously early terminating since they are time optimal both in terms of D and of. Previous communication e cient solutions were slow in the case where D. Weobserve that this is the most typical case. Preliminary reports of parts of the work reported here appeared in the proceedings of the ICCC 88
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