Dynamic Performance of ALOHA-Type VS AT Channels: A Simulation Study

This paper presents a simulation study of the dynamic behavior of ALOHA-type protocols used in interactive-data very small aperture terminal (VSAT) networks. A simulation model for quantitative evaluation of random access channel stability in terms of the transient response to a traffic overload pulse is described, and the usefulness of a single performance measure defined as “backlog fall time” is established. The variation of backlog fall time with selectable protocol parameters (such as average retransmission delay for nonadaptive systems or retransmission backoff policy parameters for adaptive systems) is investigated, for example, ALOHA and selective reject (SREJ) ALOHA channels. A methodology for joint optimization of steady state and dynamic performance based on obtaining contours of average delay versus backlog fall time over the variation range of selectable protocol parameters is outlined and demonstrated. It is shown that, generally speaking, a suitable operating point is easily identified from these contours because they exhibit a characteristic “knee” region in which both delay and fall time are close to the minimum values that can be independently obtained.