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.