Abstract

In this paper, we present the results of a study of routing algorithms for traffic restoration after a failure in a virtual circuit packet switched wide area network capable of supporting integrated traffic (e.g., voice, video and data). The dominant factor on network performance after a failure is the transient congestion period that results from restored virtual circuits attempting to send out the entire backlog of packets accumulated since the failure. Standard routing algorithms based on minimizing the steady state network delay may not be appropriate for rerouting the calls after a failure, in view of the transient congestion. Here we propose alternative routing schemes to reduce the congestion. One approach is to use Minimum Hop routing to restore connections in order to ensure that the number of nodes directly effected by the rerouting is limited to a minimum. This method attempts to isolate and restrict the physical area of the congestion occurring due to the rerouting from a failure. An alternate approach is to distribute the potential congestion caused by the rerouting among the various links in the network, to take advantage of residual network capacity. This method allows the backlog of traffic to be potentially spread out over the various links in the network in order to not degrade the performance seriously at any particular link. This Load Distribution routing can be either across all the possible routes between the source-destination nodes or across all the links leading out of the source nodes. The results of a simulation study of a 10 node network comparing the performance of the different routing algorithms (i.e., Minimum Delay, Minimum Hop, Load Distribution on Paths, Load Distribution on Links) are presented.

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