Exact and approximate analysis of DQDB under heavy load

The distributed queue dual bus (DQDB) standard is studied under heavy load conditions. The DQDB protocol for asynchronous traffic is reviewed. The network model and analysis are presented when there are two active nodes. Analytic expressions are derived for the steady-state nodal throughputs and the average value of the request counters of inactive nodes. The three-station case is considered by providing an accurate approximation for the situation when the third node is in between the two initially active nodes. Simulation results are given for comparison. The effect of the position of a node was studied via simulation in the three-station case. The case when one of the active nodes becomes inactive in a network with three initially active nodes is analyzed. The state the network assumes is studied in terms of nodal throughputs after one of the nodes turns off, and the impact on the request counters of the inactive nodes are investigated