3-tier structured access protocol to control unfairness in DQDB MANs

This paper addresses the unfairness problem appearing in 802.6-based DQDB MANs. Traffic load demand is characterized as low (below 0.4 of the channel capacity), normal (from 0.4 to 0.9 of the channel capacity) or heavy (greater than 0.9 of the channel capacity). At low loads the 802.6 protocol is acceptably fair. At normal loads, however, the protocol performance is markedly unfair. The unfairness is related to the latency in transporting a request. At heavy loads the unfairness is both latency-related and flooding-related. In this paper, both types of unfairness are carefully analyzed. As a control measure, a 3-Tier Structured Access protocol is proposed. At low loads the 802.6 performance is retained. For normal loads, extra slots are allowed based on predicted demand. At heavy loads access protection is applied. A Dynamic Assessment of Network Topology (DANT) protocol is also presented. The DANT dynamically maintains the additional information required for the implementation of the 3-tier structure. The proposed fair access protocol is studied under different load types and traffic demand. A tuning scheme is proposed... Read complete abstract on page 2.