A delay analysis of FDQ (Fair Distributed Queue) and DQDB networks

Abstract

A delay analysis of FDQ (Fair Distributed Queue) and DQDB (with and without the BWB mechanism) is presented. A network of two active nodes with a large separation of nodes is considered in each case. Under the common set of assumptions of single buffer nodes, geometric arrivals and the packet size of one segment, the mean delay at each node is obtained using limited independence assumptions. Results from the analyses are compared to simulation results. The analyses are shown to be quite accurate for low to moderate loads and they only require the solution of polynomial equations. The mean delays at both stations under FDQ with equal arrival rates are shown to be almost equal. DQDB and DQDB with BWB have increasingly asymmetric mean delays with higher arrival rates. For a dual bus implementation, the mean delay at the upstream station is less than that at the downstream station for all three protocols. FDQ has the smallest difference between the two stations' delay results and DQDB has the highest in this case.