Performance evaluation of DQDB+/- metropolitan area networks supporting isochronous and nonisochronous traffic

The distributed queue dual bus (DQDB) protocol is the media access protocol of the IEEE 802.6 standard for metropolitan area networks. DQDB suffers from two major drawbacks, namely, low bandwidth utilization of the buses and slowly converge to a fair distribution of the bandwidth to the stations. DQDB+/- is one of the modified protocols that aim at minimizing these drawbacks. The current paper investigates the behavior of the DQDB and DQDB+/- when transmitting isochronous and nonisochronous traffic, while preserving the service requirements for each of them. The simulation results indicate that both of the two protocols perform better when dealing with isochronous traffic than with nonisochronous traffic. The performance measures restricted on evaluating the delay, the throughput, the loss probability and the maximum number of traffic sources the network can support regarding the quality of service (QOS) requirements. The results of DQDB+/- are obviously superior to DQDB.