In this paper, we present an approximate model (with finite or infinite waiting room) for an integrated service system with three types of traffic: a first offered narrow-band traffic, an overflow narrow-band traffic and a wide-band traffic. A narrow-band call requires a single server, while the number of servers required to serve a wide-band call is N. The blocked narrow-band calls are lost while the blocked wide-band calls are delayed in a finite or infinite waiting room. Based on two assumptions with regard to the characteristics of the system, we resolve the system by decomposition. The corresponding improvements in numerical efficiency as well as in computational storage requirements are significant enough to enable use of the model within network optimization algorithms. The model provides a very good approximation for the
system performance, that is the blocking probabilities of the two narrow-band traffics, the loss probability (in the case of finite waiting room), the
probability of nonwaiting and the average waiting time of wide-band traffic.
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