All-to-all broadcast by flooding in communications networks

The author establishes the worst-case time complexity of all-to-all broadcast, which involves the simultaneous broadcast of messages from each node in a network to each other node, as with the dissemination of network status information for adaptive routing in ARPANET, by flooding. It it shown to be almost two times the optimum. This suboptimality of flooding results from the selection method permitting some message(s) to be consistently blocked by others. It is possible to avoid such blocking and attain the optimal worst-case time complexity by flooding within a spanning subtree. Simulations examine the performance of all-to-all broadcast by flooding using different selection methods. The best overall performance came using random selection, with FIFO next best, followed by LIFO, and in-order last. This relative performance is consistent with the hypothesis that flooding will generally perform better if implemented with a selection method that tends to avoid having some message(s) consistently blocked by others. Simulations show that the optimal worst-case time complexity is rarely exceeded, and then by only a relatively small amount