On the access fairness of the DQDB MAN protocol

To study the access fairness in the DQDB (distributed queue dual bus) protocol of the IEEE 802.6 MAN (metropolitan area network), a generalized version of the protocol is considered. In the generalized version, the access control field of a slot contains multiple request bis (REQs), and each station uses multiple countdown counters up to a maximum number called the threshold. Simulation results show that with just one additional REQ over the original protocol, the channel capacity is allocated almost evenly among the stations. If the cumulative input rate does not exceed the channel capacity, the original protocol induces acceptably fair mean-waiting-time performance for both symmetric and asymmetric loads, and for long propagation delays. If the channel capacity is exceeded, the use of additional REQs and countdown counters can improve performance fairness