INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS Int. J. Commun. Syst. 2004; 17:1–26 (DOI: 10.1002/dac.623) On the effectiveness of alternative paths in QoS routing Yanxia Jia y , Ioanis Nikolaidis z and Pawel Gburzynski },n Department of Computing Science, University of Alberta, Edmonton, AB, Canada T6G 2E8 SUMMARY We propose a routing strategy in which connection requests with specific bandwidth demands can be assigned to one of several alternative paths connecting the source to the destination. The primary goal of this multiple-path approach is to compensate for the inaccuracy of the knowledge available to routing nodes, caused by the limited frequency of link state (LS) information exchanges. We introduce a collection of K-shortest path routing schemes and investigate their performance under a variety of traffic conditions and network configurations. We subsequently demonstrate that K-shortest path routing offers a lower blocking probability in all scenarios and more balanced link utilization than other routing methods discussed in the literature. With our approach, it is possible to reduce the frequency of link state exchanges, and the incurred bandwidth overhead, without compromising the overall performance of the network. Based on the proposed routing scheme, we investigate different link state dissemination algorithms, which are aimed at reducing the communication overhead by prioritizing the scope and differentiating the qualitative content of LS update messages. Copyright # 2004 John Wiley & Sons, Ltd. KEY WORDS: QoS; routing; resource allocation; multiple-path routing; link state; flooding 1. INTRODUCTION 1.1. Quality of service routing With the growing diversification of networking applications and proliferation of integrated services, networks are being forced to cater to a variety of traffic classes with definite and often critical quality of service (QoS) requirements. Nowadays, it becomes more and more evident that the QoS requirements of modern networking applications can no longer be ignored by routing algorithms [1], with their objective being redefined as selecting the optimum path between source and destination that satisfies certain (possibly multiple) QoS constrains. The application of constraint-based routing is seen as central to providing QoS in internetworks, such as the current Internet. Proposed solutions include modifications to the shortest path first (SPF) scheme by adding additional constraints that an edge (link) must satisfy in order to be Received 10 July 2003 Revised 20 August 2003 Accepted 12 September 2003 Copyright # 2004 John Wiley & Sons, Ltd. } E-mail: pawel@cs.ualberta.ca n Correspondence to: P. Gburzynski, Department of Computing Science, University of Alberta, Edmonton, AB, Canada T6G 2E8. y E-mail: yanxia@cs.ualberta.ca z E-mail: yannis@cs.ualberta.ca