Cost / Performance Trade-Offs and Fairness Evaluation of Queue Mapping Policies

Whereas the established interconnection networks (ICTN) achieve low latency by operating in the linear region, i.e. oversizing the fabric, the recent strict cost and power constrains demand more efficient utilization of future networks. Increasing the utilization of lossless ICTNs may, however, lead to saturation and performance degradation owing to HOL-blocking. The current solution to HOL-blocking consists of using Virtual Output Queueing (VOQ), whose quadratical scalability is expensive in large networks. To improve VOQ’s scalability we have proposed the Destination-Based Buffer Management (DBBM), a scheme that compares well with VOQ. Whereas previously we have analyzed DBBM’s basic operation and performance, in this paper we have set two different goals. First we focus on how the different DBBM mappings can impact the cost/performance of multistage ICTNs. Next, because DBBM can introduce unfairness, this constitutes the second theme of our paper. The new results show that DBBM with modulo-4/8 mapping performs very well for only a fraction of the VOQ cost. Also in terms of fairness DBBM shows promise, because it (i) keeps the unfairness degree independent of both topology and routing, while (ii) minimizing the number of flows affected by unfairness.