Distributed admission control for supporting isochronous traffic in DQDB MANs

Distributed queue dual bus (DQDB) metropolitan area networks (MANs) provide data and isochronous services using the connection-less queued arbitrated (QA) and connection-oriented pre-arbitrated (PA) access schemes, respectively. Essentially, the DQDB-PA scheme adopts a connection management procedure which requires laborious exchanges of control messages. Besides, the scheme disregards how bandwidth is allocated for each type of traffic. This paper proposes a distributed admission control (DAC) mechanism for supporting isochronous traffic in DQDB MANs. DAC is composed of two components, the bandwidth allocator and the connection manager. Based on a Markovian model, the bandwidth allocator dynamically allocates appropriate bandwidth to isochronous data according to the current and imminent isochronous traffic load. The bandwidth allocator consequently assures a given quality of service (QOS) requirement of the isochronous traffic with respect to the blocking probability. Moreover, requiring no direct confirmation exchanges, the connection manager allows connections to be admitted and disconnected in an implicit and distributed manner. Finally the paper also presents simulation results which demonstrate the performance superiority of DAC with respect to a set of QOS indexes, such as call admission delay, call blocking probability, and aggregate system throughput.