Performance evaluation of the extended distributed queueing protocol for MAN

Scheduling in a network is different from scheduling in a centralised environment where all resource requests are immediately known to the centralised scheduler. In metropolitan or wide area networks communication delays can be long and scheduling has to be carried out in parallel by distributed nodes with partial or delayed information. The extended DQDB protocol proposed by Budrikis for the accommodation of connection oriented time critical services, tries to augment the degree of resource utilisation of a dual bus shared medium network while meeting the quality of service requirements. The performance of the extended DQDB protocol will be compared to the performance of the queueing discipline the protocol tries to implement. We study the impact of internode distance and loading conditions on access delay distribution and demonstrate the effect of the presence of low priority traffic on the high priority traffic delays. These measurements are performed on a simplified centralised queueing model and on a detailed simulation model for the DQDB and the discrepancies between target and reality are discussed