Call establishment overload in large ATM networks

The call establishment process in asynchronous transfer mode (ATM) networks can constitute a source of overload in the switches of the network. The purpose of this paper is to use analytic modeling and simulation to investigate this effect. The call establishment overload can be particularly significant when the network will contain a relatively large number of switches, due to the inaccuracy of the information available to the switch accepting or rejecting the call, and because of the multiple paths which need to be assessed and then utilized to establish the call. We simulate the call set-up phase of an ATM connection, including path selection, bandwidth reservation and call rejection, and simulate the flow of call establishment messages to estimate by simulation and analytically the queue lengths of call establishment processing at the input, output and intermediate switches. Average usage of bandwidth at the links, and the probability that a call request is rejected due to insufficient capacity at some link, are measured via simulation and also predicted using an analytical model. Simulation results show that if bandwidth is not reserved at input nodes, very large queues of call establishment jobs can build up in the switches of the network. A simplified analytical model is derived to estimate the queue lengths of call establishment jobs at each node of the network when advanced reservation with perfect information is implemented. Simulation results are compared to approximate model predictions for each individual switching node in a 100-node (switch) ATM network model. It is shown that the analytical model dealing with a large ATM network can qualitatively predict the locations of queue build-up of jobs for call establishment processing, with accurate queue length predictions for being made in the case of light traffic load. The analytical model provides a lower bound to queue lengths, and remains within the same order of magnitude when the call request traffic is high.