Description
Advances in microprocessor technology will soon make general purpose computing systems composed of thousands of VLSI processors economically feasible. A high-performance communication system to interconnect these processors is of crucial importance to exploit the parallelism inherent in application such as circuit simulation and signal processing. This thesis discusses issues in the design of universal VLSI communication components to be used as the building blocks for constructing robust, high-bandwidth, point-to-point networks. The components provide enough flexibility to serve a wide variety of multicomputer configurations and applications. They feature special purpose hardware to implement communication functions traditionally implemented with network software.
A communication network constructed from the proposed components is modeled as a set of nodes (components) connected by bidirectional communication links. Because of technological constraints, the total I/O bandwidth of each node is limited to some fixed value, and assumed to be equally divided among the attached links. Increasing the number of links per component leads to a reduction in the average number of hops between nodes, but at the cost of reduced link bandwidth. This "hop count/link bandwidth" tradeoff is examined in great detail through M/M/1 queueing models and simulations using traffic loads generated by parallel application programs. These results indicate that a small number of links should be used. It is also found that a significant improvement in performance is obtained if a component is allowed to immediately begin forwarding a message when the selected output link becomes idle, regardless of whether or not the end of the message has arrived. Finally, mechanisms which efficiently transmit a single message to multiple destinations are seen to have a significant impact on performance in programs relying on global information.
The complexity of the circuitry required to implement a communication component is examined. Schemes for providing hardware support for communication functions -- routing, buffer management, and flow control -- are presented. Estimates of the number of buffers and the degree of multiplexing on each communication link are determined. The amount of circuitry to implement a communication component is computed, and it is seen that the proposed communication component could be complemented with technology available today. Design recommendations for the implementation of such a component are made.