Evaluating the impact of stale link state on quality-of-service routing

Quality-of-service (QoS) routing satisfies application performance requirem ents and optimizes network resource usage by selecting paths based on conne ction traffic parameters and link load information. However, distributing l ink state imposes significant bandwidth and processing overhead on the netw ork. This paper investigates the performance tradeoff between protocol over head and the quality of the routing decisions in the context of the source- directed link-state routing protocols proposed for IP and ATM networks. We construct a detailed model of QoS routing that parameterizes the path-selec tion algorithm, link-cost function, and link-state update policy. Through e xtensive simulation experiments with several network topologies and traffic patterns, we uncover the effects of stale link-state information and rando m fluctuations in traffic load on the routing and setup overheads. We then investigate how inaccuracy of link-state information interacts with the siz e and connectivity of the underlying topology. Finally, we show that tuning the coarseness of the link-cost metric to the inaccuracy of underlying lin k-state information reduces the computational complexity of the path-select ion algorithm without significantly degrading performance. This work confir ms and extends earlier studies, and offers new insights for designing effic ient quality-of-service routing policies in large networks.