Access protection solution for heavy load unfairness in DQDB

This paper discusses the unfairness issue arising in an 802.6 DQDB network at heavy loads — when traffic demand exceeds bus capacity. At heavy loads, the end-nodes along a bus experience longer delays than the other nodes. The origin and remedy of this heavy load unfairness are discussed. Using the information about the node population and the position of individual nodes, an effective access protection scheme (APS) is formulated to counter the heavy load unfairness. A comparison of the proposed scheme with the 802.6 protocol (with and without a bandwidth balancing mechanism — BWB) is presented. The performance characteristics are investigated with different load types. With symmetric load conditions, under the APS protocol, all nodes along a bus experience fairly uniform access delay and packet loss characteristics. The bandwidth achieved by the individual loads also follows a symmetric pattern. Thus, the APS outperforms the BWB balancing mechanism at symmetric loads. Performance under several other load conditions is also found to be reasonable. The APS inherits the potential for dynamic bandwidth control, and such a scheme is outlined. Accordingly, a tunable parameter (α) may help serve non-symmetric demand patterns better.