Rate Assignment in Micro-Buffered High Speed Networks

Micro-buffered networks are high speed optical packet switched networks, and consist of either nodes with no buffering or nodes with limited buffering. We focus on the case of bufferless nodes, where there is no specific collision resolution mechanisms inside the core. Packet losses inside the core may be frequent, and are dealt with using end-to-end or edgeto-edge coding techniques. In this study, we discuss the rate allocation problem for a micro-buffered high speed network. Various rate assignment policies are defined and related features and algorithms are discussed. First the classical slotted aloha type protocols with exponential backoff are examined and it is observed that in the case of asymmetry in collision sets, classical aloha protocols with exponential backoff may result in unfair rate allocations such that some flows may end up with zero rates. Next, we consider (weighted) α-proportional , (weighted) max-min and hierarchical max-min fair rate assignments. Simple distributed algorithms achieving these notions of fairness by exchanging local information are discussed. It is found that (weighted) max-min fair information rate allocation assigns information rates to each flow in the same group inversely proportional to their weights, where groups correspond to connected components in the contention graph between flows. As a special case, max-min fairness assigns the same information rate to any two flows in the same group even though they do not directly contend with each other. Furthermore, we also show that hierarchical max-min fairness can be achieved in a micro-buffered network if and only if weighted max-min fairness among the flows is ensured.