The problem of routing in a circuit-switched network with different classes of traffic is examined. The authors consider the case of two priority classes, assuming that a relatively small fraction of traffic comprises the high-priority class requiring a better grade of service, with the rest being treated as lower priority normal traffic. These high-priority calls might be used to provide a premium service with lower blocking probability, or to implement services in which failure is expensive to the network such as a multiparty conference call. The authors identify several routing schemes that give preference to high-priority calls, either by explicitly reserving capacity or by allowing more resource sharing. The performance of these schemes is studied in terms of blocking probabilities for the two classes, protection of priority traffic against overload of normal traffic, and adaptability to variations in offered priority traffic. The authors compare the schemes by the different total revenues they earn and discuss the implementation complexity. They find that some resource-sharing schemes display good performance, having the potential to provide low blocking for priority calls with minimal impact on the remaining normal traffic.
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