Cycle compensation protocol: A completely fair protocol for the uni-directional twin-bus architecture

The IEEE 802.6 Standard Distributed Queue Dual Bus (DQDB) for metropolitan area networks (MANs) is considered. It is based on a unidirectional twin-bus architecture. The DQDB protocol lays more emphasis on the overall channel utilization than the fair sharing of channel bandwidth by all the stations. The resulting unfairness problem in which the upstream stations occupy most of the channel bandwidth while the downstream stations get fewer chances to transmit their packets is discussed. Many previously proposed possible fixes are also reviewed. However, these schemes either have a lower performance or cannot guarantee complete fairness when the ratio of end-to-end propagation delay to the slot-size is large. A cycle compensation protocol which ensures complete fairness regardless of the ratio of end-to-end propagation delay to the slot size is described. This proposed protocol also achieves almost the same performance as that of DQDB.