Performance evaluation of a bundle spacer

In [1], a Medium Access Control protocol for a passive optical network, realizing shared access to an ATM network, was proposed. Besides ensuring a fair access, the protocol also incorporates a spacing function. As the access system has only knowledge about VP´s (and not about individual VC´s), it can only space a bundle of VC´s. In this paper, we isolate this bundle spacer and investigate its performance. It was already shown in [11 that spacing according to the sum of the peak bit rates of the individual Ws may lead to unacceptable waiting times introduced by the spacer. This would suggest the use of small spacing times. On the other hand, spacing is needed to reduce the clumping of cells introduced by previous multiplexing stages. In order to find optimal values for the spacing time, we study the following system. We let the bundle of Ws consist of background Ws (modeled by e.g. Poisson traffic) and a tagged VC, and study the reduction of the clumpedness by the bundle spacer through an analysis of the cell stream of the tagged VC at the output of the spacer. We investigate three performance measures :