The fairness issue in the CRMA-II MAC protocol

Simulation is used to investigate the behavior of the \global fairness" algorithms proposed for CRMA-II, a MAC protocol for very-high-speed networks devised by IBM for the local and metropolitan environments. Results indicate that too strictly enforcing global fairness may result in undesirable short-term and long-term behaviors. However, when we consider that guaranteeing global fairness is impossible due to the niteness of the metrics stored at each node, we see that the fairness control algorithms of CRMA-II can provide acceptable performance. One interesting general question arising from the observed behaviors is whether fairness control mechanisms should address \global" or \instant" fairness , that is whether they should aim at equalizing the usage of network resources over either very long or relatively small time intervals.