Improved Medium Access Control for Data Traffic via Satellite Using the Cfdama Protocol

This paper explores an efficient Medium Access Control protocol for carrying data traffic via satellite. The Combined Free/Demand Assignment Multiple Access (CFDAMA) protocol combines free assignment of data slots with demand assignment, providing a minimum delay of one round trip time at low loads and the statistical multiplexing gains of demand assignment at high loads. The delay/utilisation performance of CFDAMA is explored for both Poisson and selfsimilar traffic models. It is shown for Poisson traffic that CFDAMA provides both extremely low end-to end delay and variance in delay of packet transmissions over a wide range of loads up to 85% of the channel capacity. For self-similar traffic, it has been found that the scheme is limited to a lower maximum channel loading, but performs better at low channel loads. The importance of an accurate traffic model in network performance evaluation is highlighted. Comparisons are made between CFDAMA and the Slotted ALOHA protocol, and it is shown that CFDAMA outperforms Slotted ALOHA over virtually the entire range of channel utilisation.