A study of deadlock models for a multiservice medium access protocol employing a Slotted Aloha signalling channel

Medium access protocols for HFC and wireless ATM networks often use a collision based capacity request signalling channel which may rely on the slotted Aloha multiaccess principle. This paper studies the performance of a p-persistence slotted Aloha contention resolution algorithm (CRA), subject to extreme interstation correlation, by means of a discrete-time Markov chain analysis. We examine in detail the conditions leading to a deadlock-a situation where the time to collision resolution becomes unacceptably high and the system is practically unstable. We analyze two disaster scenario deadlock models, and study the effect of channel error probability, signalling traffic load, and the contention resolution algorithm used. We show that the key factor of the CRA is the collision rate and not channel errors. We propose and test three signalling channel capacity allocation schemes. We identify the best-performing of these three schemes as the cyclic contention mini-slot (CMS) sharing employing multiple CMSs per data slot. Finally, we demonstrate the need for implementation of an added scheme, which dynamically adjusts the p-persistence parameter.