Joint optimization of steady state and dynamic performance of ALOHA-type VSAT channels

Abstract

An investigation is made of the stability and dynamic behavior of ALOHA-type protocols used in very small aperture terminal (VSAT) networks that support bursty, interactive data sources. A simulation model has been developed for dynamic performance analysis of unslotted ALOHA and selective reject (SREJ) ALOHA channels and used to obtain quantitative measures of stability in terms of transient response to pulsed traffic overload. For a typical 56-kb/s interactive station VSAT channel, the dependence is examined of pulse response (summarized in terms of a quantity called the backlog fall time) on selectable protocol parameters such as average transmission delays for nonadaptive systems or backoff policy parameters for adaptive systems. These results are augmented with average delay simulations, to obtain characteristic delay versus fall-time contours that permit the designer to select protocol parameters yielding the optimum combination of nominal steady-state and dynamic performance. For the ALOHA and SREJ-ALOHA channels under consideration, a surprisingly well-defined optimum region (in the form of a knee in the delay versus fall-time curves) is generally found to exist, underscoring the value of the joint steady-state/dynamic response design methodology proposed.<>