Hierarchical routing with QoS

We present our simulation-based design of hierarchical routing systems using the following state parameters to support quality of service (QoS): delay, hop count, and available bandwidth. Without revealing its internal structure, a cluster in a hierarchical system can advertise to other clusters its transit QoS characteristics in terms of the state parameters of either minimum-weight paths or widest paths between each of its border-node pairs. Neither of these paths reflects accurately what is actually available inside a cluster to meet user QoS requirements, potentially resulting in sub-optimal routing. Moreover, based on operational experience, we show that advertising widest paths may interfere with normal operational procedures in the addition or deletion of links. After analyzing the pros and cons of these paths, we propose the use of constrained minimum-weight paths for advertisement, to balance the need for smaller weights and sufficient available bandwidth.