A multiple-priority scheme for distributed queue dual bus networks

Studies have shown that earlier versions of the distributed queue dual bus (DQDB) exhibited asymmetric segment access delay under heavy loads. A bandwidth balancing (BWB) mechanism was subsequently adopted to improve the access delay characteristics of DQDB. This mechanism, however, does not effectively support multiple levels of priority that DQDB may need in order to provide new services to the network users. This paper introduces an efficient mechanism to augment and enhance the operations of the current BWB mechanism. Simulation results have shown that with minor modifications to the current BWB mechanism, the DQDB protocol will be able to support multiple priority traffic. These modifications are shown to have no adverse effects on the access delay characteristics of the current DQDB protocol. In fact, results indicate that the proposed mechanism has better performance under light and asymmetric load conditions. In addition, the proposed mechanism can be implemented without any modification to the DQDB slot format and incurs minimal added complexity