ACCESS PROTECTION SOLUTION FOR HEAVY LOAD UNFAIRNESS IN DQDB

This paper discusses the unfairness issue arising in an 802.6 DQDB net work at heavy loads - when traffic demand exceeds bus capacity. At hea vy loads, the end-nodes along a bus experience longer delays than the other nodes. The origin and remedy of this heavy load unfairness are d iscussed. Using the information about the node population and the posi tion of individual nodes, an effective access protection scheme (APS) is formulated to counter the heavy load unfairness. A comparison of th e proposed scheme with the 802.6 protocol (with and without a bandwidt h balancing mechanism - BWB) is presented. The performance characteris tics are investigated with different load types. With symmetric load c onditions, under the APS protocol, all nodes along a bus experience fa irly uniform access delay and packet loss characteristics. The bandwid th achieved by the individual loads also follows a symmetric pattern. Thus, the APS outperforms the BWB balancing: mechanism at symmetric lo ads. Performance under several other load conditions is also found to be reasonable. The APS inherits the potential for dynamic bandwidth co ntrol, and such a scheme is outlined. Accordingly, a tunable parameter (a) may help serve non-symmetric demand patterns better.