A fair featured metropolitan area network

Abstract

An architecture and a media access control (MAC) protocol aimed at improving fairness in dual-bus networks are introduced. The major feature of this proposal is that the distributed operation of updating the queue is made atomic, so that the average bus access delay is equalized over the network. An equalized access gain is provided by mandating that a station waiting for transmission consider itself as positioned in the distributed queue only after a constant delay, which is needed for all the other stations to register the request of the first one. This delay is equal to the propagation time of the request along the entire bus. It is shown that under certain conditions the average access delay results in the one experienced in the distributed queue dual bus (DQDB) by those stations which are placed at the middle of the bus. Consequently, the global end-to-end delay remains much below the limits fixed by the CCITT for delay sensitive services. The actual average delay is even smaller than the one estimated due to the presence in the protocol of the stand-by mechanism which is the same as in the DQDB version. In comparison with the traditional DQDB, the increase in access-delay values is rewarded by the significant improvement in terms of fairness. >