Priority mechanism for the DQDB network

An efficient priority mechanism should allow high priority traffic to completely shut out all low priority traffic, if necessary, to satisfy the former´s bandwidth requirements. The DQDB priority mechanism does exactly that if the high priority traffic nodes are upstream from the low priority traffic nodes. However, it may fall short of satisfying the above property if there is at least one low priority traffic node upstream from the high priority traffic nodes. This paper proposes a modification to the implementation of the priority mechanism in DQDB that will make it perform satisfactorily. That is, a protocol that favours nodes with higher priority traffic over ones with lower priority traffic. The mechanism requires that requests carry the segment priority, as implemented in the DQDB network. In addition, it requires that the segments carry an indicator of their own priority. Performance of the protocol is studied using simulation under heavy and moderate loads