Supporting dynamic inter-class resource sharing: a multi-class QoS routing algorithm

In an integrated services network, resources are shared by multiple traffic classes. Service classes that deliver quality-of-service (QoS) to applications have priority over others that do not. In such a multi-service network, routing decisions for high priority QoS traffic will affect what resources are available for lower priority traffic: poor route selection can result in congestion for, or even starvation of, lower priority traffic. Whereas many studies have focused on routing algorithms that optimize the network throughput for individual service classes, little effort has been devoted to routing algorithms that address inter-class resource sharing. In this paper, we propose a routing algorithm that allows dynamic sharing of link resources among multiple traffic classes. The algorithm is based on the concept of "virtual residual bandwidth", which is derived from the link residual bandwidth by taking the congestion condition of low priority traffic into account. By using the virtual residual bandwidth in the link cost function for QoS sessions, we discourage QoS sessions from using links that are heavily loaded with low priority traffic. Our approach is simple in the sense that besides changing the link cost function, no other changes to the routing algorithms for individual service classes are required. An extensive simulation study shows that when the traffic load is unevenly distributed, significant performance improvements can be achieved for low priority traffic without sacrificing performance for high priority traffic. The result demonstrates that QoS routing is important even when the QoS traffic load is light and call blocking is not an issue.