A number of important questions remain concerning the scalability of networks with quality of service guarantees. We consider one of these questions: can QoS routing protocols scale to large networks? To address this question, we evaluate the performance of techniques that can reduce the QoS routing protocol overhead. We specifically focus on topology aggregation, which can reduce overhead by orders of magnitude. We also investigate the interaction of topology aggregation with other important factors that contribute to performance, such as routing update frequency, routing algorithms, and network configuration. Our experiments are based on simulations of relatively large, structured networks. Among our observations, we find-contrary to intuition-that topology aggregation does not always have a negative impact on routing performance. Aggregation can reduce the routing information fluctuation, increase stability, and thus benefit routing performance. We also propose two new methods of aggregating routing information. Our hybrid aggregation method performs much better than conventional star aggregation and approaches unaggregated performance. Our weighted aggregation method, while intuitively appealing, offers mixed performance across topologies.
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