Static and Dynamic Path Selection on Expander Graphs: A Random Walk Approach

This paper addresses the problem of virtual circuit switching in bounded degree expander graphs. We study the static and dynamic versions of this problem. Our solutions are based on the rapidly mixing properties of random walks on expander graphs. In the static version of the problem an algorithm is required to route a path between each of K pairs of vertices so that no edge is used by more than g paths. A natural approach to this problem is through a multicommodity flow reduction. However, we show that the random walk approach leads to significantly stronger-results than those recently obtained by Leighton w x and Rao Proc. of 9th International Parallel Processing Symposium, 1995 using the multicommodity flow setup. In the dynamic version of the problem connection requests are Ž continuously injected into the network. Once a connection is established it utilizes a path a . virtual circuit for a certain time until the communication terminates and the path is deleted. Again each edge in the network should not be used by more than g paths at once. The dynamic version is a better model for the practical use of communication networks. Our random walk approach gives a simple and fully distributed solution for this problem. We show that if the injection to the network and the duration of connection are both controlled by Poisson processes then our algorithm achieves a steady state utilization of the network which is similar to the utilization achieved in the static case situation. Q 1999 John Wiley & Sons, Inc. Random Struct. Alg., 14, 87]109, 1999 Correspondence to: A. Frieze *Supported in part by NSF Grants CCR-9225008 and CCR-9530974. Q 1999 John Wiley & Sons, Inc. CCC 1042-9832r99r010087-23 87 BRODER, FRIEZE, AND UPFAL 88