Distributed Queuing Dual Bus (DQDB) is a media access control (MAC) technique, which is being considered by the IEEE 802.6 for the metropolitan area network (MAN). The DQDB medium access technique has many promising advantages over other access methods. However it has one drawback, which is its unfairness in terms of node-dependent medium access delay.

In this paper a mathematic model is formulated to describe this detrimental behavior of DQDB. The access control method is first modeled as a M/G/1 queueing system with a single priority level, then it is remodeled as a non-preemptive priority system with three priority levels. By employing these models, the approximate medium access delay analysis of a DQDB network is investigated for a metropolitan area network containing 50 stations with a channel bandwidth of 150 Mbps. Numerical results are then presented to illustrate the network unfairness performance under various traffic intensities and under different priority levels. The results have been obtained for non-isochronous (asynchronous) traffic.