Connection-based adaptive routing using dynamic virtual circuits

High-bandwidth, low-latency communication is the key to delivering high performance in scalable multicomputers and clusters, which consist of compute nodes that include communication switches interconnected via point-to-point links. With advancing semiconductor technology, the rate at which processors generate and consume traffic is increasing. Future designs must exploit the increasing number of transistors per chip to also achieve higher performance in the communication subsystem, matching the needs of faster CPUs. Two techniques that can use additional hardware resources to improve network performance are adaptive routing and connection-based routing. Adaptive routing may change traffic routes to avoid congestion or faults. Connection-based routing can reduce packet processing overhead by reserving resources prior to communication. Most connection-based routing schemes, such as traditional virtual circuits, are static---once a connection is established, it remains fixed for its lifetime. This thesis presents a new mechanism that combines the advantages of adaptive routing and connection-based routing for arbitrary topologies. The proposed Dynamic Virtual Circuit (DVC) mechanism allows existing connections to be quickly torn down in order to release resources needed for others or to be reestablished along routes that are better for current network conditions. The challenges for the DVC mechanism are to efficiently retain connection semantics despite rerouting, and to avoid or resolve protocol or packet buffer deadlocks. A previous approach for deadlock resolution is extended for use in DVC networks, and its performance limitations are identified. Subsequently, a competing deadlock avoidance technique is developed. It is based on unconstrained routing of DVCs combined with a deadlock-free virtual network. Simulations show that with DVCs, global routing optimization is possible and provides performance superior to fixed routing. The use of deadlock-free escape paths is sufficiently infrequent to preserve the bandwidth efficiencies of the DVC mechanism. Connection-based adaptive routing may be beneficial for different networking environments. We evaluate the potential of such routing to reduce packet loss in large multi-path ATM or IP switches. With the class of traffic patterns considered, the results show that routing of the heaviest flows can lead to significantly lower cell loss than oblivious distribution.