Adaptive Bandwidth Balancing Mechanisms for DQDB Networks

To improve fairness in distributed queue dual bus (DQDB) metropolitan area networks a mechanism known as bandwidth balancing (BWB) has been introduced in the final version of the IEEE 802.6 standard document. Since then several changes to the basic mechanism, attempting to adhere to different interpretations of the fairness concept and to match the needs of different categories of users, have been proposed. In this paper attention is focused on the adaptive class of fairness control mechanisms and two solutions are analysed and compared. In order to do this, analytical models suited to the study of DQDB networks under overload conditions are introduced. The models are also amenable to the evaluation of the transient behaviour of DQDB networks, thus enabling a thorough investigation of the performance that can be obtained by adopting different fairness control mechanisms. The analytical models have been validated through the use of a software simulator. Numerical indices measuring the performance of the balancing mechanisms mentioned above are also given.