Fair Bandwidth Allocation in Multiple Priority DQDB Networks

The Distributed Queue Dual Bus (DQDB) protocol has been adopted as the IEEE 802.6 standard for Metropolitan Area Networks (MANS). A MAN operates at a much higher speed than a LAN does and covers a large geographical area. The original DQDB protocol exhibits unfair bandwidth allocation under overload condition. To solve the problem, the Bandwidth Balancing scheme (BWB) has been incorporated in the standard. However, the BWB scheme suffers from low channel utilization and long transient time. Moreover, the BWB fails to ensure fair bandwidth allocation in a multiple priority network. In this paper, we propose an algorithm, MP-NSW, that improves the fair bandwidth allocation in a multiple priority DQDB network. MP-NSW requires only minor modifications to the DQDB protocol, and is easy to implement. The simulation results show that the MP-NSW has fairer bandwidth allocation in a multiple priority network than the BWB scheme does. The MP-NSW can also achieve a 100’7 channel utilization which results in lower access delay !or downstream hlgh priority nodes.