Delivery of time-critical messages using a multiple copy approach

Reliable and timely delivery of messages between processing nodes is essential in distributed real-time systems. Failure to deliver a message within its deadline usually forces the system to undertake a recovery action, which introduces some cost (or overhead) to the system. This recovery cost can be very high, especially when the recovery action fails due to lack of time or resources. Proposed in this paper is a scheme to minimize the expected cost incurred as a result of messages failing to meet their deadlines. The scheme is intended for distributed real-time systems, especially with a point-to-point interconnection topology. The goal of minimizing the expected cost is achieved by sending multiple copies of a message through disjoint routes and thus increasing the probability of successful message delivery within the deadline. However, as the number of copies increases, the message traffic on the network increases, thereby increasing the delivery time for each of the copies. There is therefore a tradeoff between the number of copies of each message and the expected cost incurred as a result of messages missing their deadlines. The number of copies of each message to be sent is determined by optimizing this tradeoff. Simulation results for a hexagonal mesh and a hypercube topology indicate that the expected cost can be lowered substantially by the proposed scheme.