Evaluating the performability of tactical communications networks

Tactical communications networks are multihop wireless networks in which switches and endpoints are mobile nodes. In a tactical environment, system performance degrades when switching nodes and/or communication links fail to operate. Fast algorithms for performance analysis are desirable for optimizing the network in a timely fashion. Further, tactical networks commonly use preemptive priorities to achieve low blocking probabilities for high-priority calls when the loss of equipment in the battlefield is not trivial. This paper discusses three measures and analytical algorithms for the performability evaluation of a two-tier tactical communications network where preemptive priority service discipline is employed and traffic is divided into multiple classes to provide multiple grades of service. Each class of traffic has its distinct characteristics, such as average call-arrival rate, average call-holding time, and service priority. The three performability measures are devised to evaluate the impact of nodes/links failures on system performance. Experiments show that the preemption does provide robust service for higher priority traffic. The techniques for performability evaluation presented in this paper may also be useful in other rapidly deployable networks, where mobility, communication efficiency, and computational complexity for adapting the network to unpredictable environments are of significant concern.