Fair Access in WDM ring networks

Packet-based optical access ring is becoming a promising solution in metropolitan networks. Its performance depends mainly on how optical resource sharing takes place among the different competing access nodes. In such a network fairness issues are likely to arise between upstream and downstream nodes competing to access a common data channel. We analyze the system performance in terms of access delay required by each node to inject a packet on the shared medium. We observe that sharing the available bandwidth fairly and arbitrarily between nodes does not resolve the fairness problem. Consequently, an additional flow control mechanism has to be considered, not only to limit the transmission of the upstream nodes but also to organize their emission process. This paper provides a new protocol called TCARD (Traffic Control Architecture using Remote Descriptors), based on a preventive reservation scheme, to alleviate the fairness problems. The reservation process consists in forcing the upstream nodes to ensure enough available bandwidth for downstream nodes’ transmission purpose. Moreover, we develop analytical model in order to assess the access delay when TCARD is enabled. The analytical and simulation results show how the proposed solution alleviates the performance degradation and the resource sub-utilization while achieving fairness among bus nodes. Keywords—Bus-based optical access network, Medium Access Control (MAC) Protocol, Fairness control, Access delay evaluation.