Buffer Management Strategies to Reduce HoL Blocking

Congestion management is likely to become a critical issue in interconnection networks, as increasing power consumption and cost concerns lead to improvements in the efficiency of network resources. In previous configurations, networks were usually oversized and underutilized. In a smaller network, however, contention is more likely to occur and blocked packets cause head-of-line (HoL) blocking among the rest of the packets, spreading congestion quickly. The best-known solution to HoL blocking is Virtual Output Queues (VOQs). However, the cost of implementing VOQs increases quadratically with the number of output ports in the network, making it unpractical. The situation is aggravated when several priorities and/or Quality of Service (QoS) levels must be supported. Therefore, a more scalable and cost-effective solution is required to reduce or eliminate HoL blocking. In this paper, we present a family of methodologies, referred to as Destination-Based Buffer Management (DBBM), to reduce/eliminate the HoL blocking effect on interconnection networks. DBBM efficiently uses the resources (mainly memory queues) of the network. These methodologies are comprehensively evaluated in terms of throughput, scalability, and fairness. Results show that using the DBBM strategy, with a reduced number of queues at each switch, it is possible to achieve roughly the same throughput as the VOQ mechanism. Moreover, all of the proposed strategies are designed in such a way that they can be used in any switch architecture. We compare DBBM with RECN, a sophisticated mechanism that eliminates HoL blocking in congestion situations. Our mechanism is able to achieve almost the same performance with very low logic requirements (in contrast with RECN).