In this paper we present a hierarchical network model to estimatethe connection blocking for large hierarchical networks.

As networks grow in size, nodes tendto form clusters geographically and hierarchical routing schemes are morecommonly used, and it is important that network modeling methods havescale-up capabilities. Loss networks and reduced load/fixed point modelsare often used toapproximate call blocking probabilities and hence throughput in a circuitswitched network. We use the same idea for estimating connection blockingin a data network with certain QoS routing schemes. However so far most workbeing done in this area is for flat networks with flat routing schemes.

We aim at developing a more efficient approximation method for networksthat have a natural hierarchy and/or when some form of hierarchical routingpolicy is used. We present hierarchical models in detail for fixedhierarchical routing and dynamic hierarchical routing policies,respectively, viathe notion of network abstraction, route segmentation, traffic segregationand aggregation. Computation is done separately within each cluster (local)and among clusters (global), and the fixed point is obtained by iterationbetween local and global computations. We present results from bothnumerical experiments and discrete event simulations.