Analysis and design of book-ahead bandwidth-sharing mechanisms

In this article, we present a novel discrete-time Markov chain model of book-ahead bandwidth-sharing mechanisms. We use this analytical model and a simulation model to understand the benefits of book-ahead (BA) bandwidth-sharing when compared to the immediate-request (IR) call-blocking mode of bandwidth-sharing in circuit-switched networks. We study two different BA schemes, BA-all, in which the caller accepts any set of available timeslots, and BA-n, in which the caller specifies n call-initiation time options. Numerical results show that the BA-all achieves 95% utilization with a call-blocking probability of only 1%, while in the IR mode, call blocking probability is 23% even when utilization is only 80%. The BA-n schemes perform as well as the BA-all scheme if the call-initiation time options are restricted to fall on timeslot boundaries separated by the minimum call holding time. The length of the advance reservation horizon, K, is shown to increase linearly with call holding time, H. The ratio K/H is primarily dependent on the link capacity in channels. For example, if the link is divided into 10 channels, to achieve a 2% call blocking probability, the advance-reservation horizon needs to be a factor of 4 times the call holding time. In other words, the extra data storage and processing required to accept and maintain advance reservations is not significant.