Dedi Rosadi 22 A Comparison of Approximation Algorithms for Blocking Probabilities on Telecommunication System with Trunk Reservation Access Policy Dedi Rosadi Department of Mathematics, Gadjah Mada University dedirosadi@lycos.com : drosadi@mipa.ugm.ac.id Abstract It has widely known that the irreversible property of Markov chain representing the multirate multiservice loss system with Trunk Reservation policy is not satisfied. In this case, the well-known product form result for state probabilities cannot be applied. To obtain the exact state probabilities, one has to solve the balance equation of Markov chain that represents the system. But this is impractical for the computational purpose, because that equation is going to intractable if the system capacity and/or number of classes of calls increase. Therefore, this computation is mainly relying on an approximation algorithm. In this paper, we compare two approximation algorithms for computing the blocking probabilities in system employing the Trunk Reservation policy as the access strategy. Keywords: Trunk Reservation, Link Sharing Policy 1. Introduction Telecommunication systems have been evolving from the conventional telephone network, which mainly transports voice, into the ISDN system, which enables us to transport voice, data and image, and high-speed video in one network. This multi-service network is a connection-oriented network and calls of different types usually require different bandwidth. We call this system a multi-rate system. The acceptance of a new call in a multi-rate system is regulated by link bandwidth management or CAC (Connection Admission Control). By CAC, an incoming call will be accepted as long as there is a sufficient bandwidth for servicing that call. Although this admission policy is simple to describe and administer, it may lead to poor resource utilization, or to poor long-run average reward (Ross (1995)). Therefore, we consider admission control in a more advanced setting than that CAC. We call then the resource sharing mechanisms Link Sharing Policies (LSP). In general, we can say that a LSP is a set of rules to control the acceptance of an incoming call on the link. By LSP, we might restrict access to the link even when there is sufficient part of link for servicing the call. In the model, the blocking call is often considered as lost. In this case, the multirate system is called as Loss System. It turns out that introducing a resource sharing policy can increase the system's performance. It was shown, e.g. in (Fleuren and Klein-Obbink (1998) and Rosadi