DQDB under heavy load: performance evaluation and fairness analysis

An extended simulation analysis of the asynchronous part of the distributed queue dual bus (DQDB) MAC protocol is reported. DQDB is analyzed in asymptotic conditions, i.e. bandwidth sharing among network nodes when each node is trying to seize all of the medium capacity. DQDB fairness and performance is investigated under a more realistic scenario. The results show that DQDB without the bandwidth balancing mechanism (BBM) is unfair and that the unfairness is dependent on the medium capacity and the bus length. When the BBM is enabled, DQDB fairness and performance, in the steady state, improve significantly. However, DQDB takes some time to achieve the steady state, during which time the node quality of service is degraded.>