Recent studies provide evidence that Quality ofService QoS routing can provide increased network utilization compared to routing that is not sensitive to QoS requirements of tra c. However, there are still strong concerns about the increased cost of QoS routing, both in terms of more complex and frequent computations and increased routing protocol overhead. The main goals of this paper are to study these two cost components, and propose solutions that achieve good routing performance with reduced processing cost. First, we identify the parameters that determine the protocol tra c overhead, namely a policy for triggering updates, b sensitivity of this policy, and c clamp down timers that limit the rate of updates. Using simulation, we study the relative signi cance of these factors and investigate the relationship between routing performance and the amount of update trafc. In addition, we explore a range of design options to reduce the processing cost of QoS routing algorithms,...