Simulation of computer network reliability with congestion

A computer network is generally modeled by a graph consisting of nodes (computers) and links (communication lines). In practical situations, the links have finite capacity, and excess messages are stored in a finite length queue at the nodes. A link is congested if the number of packets waiting to be transmitted over the link exceeds its maximum queue length. The network can fail due to excessive delays in a queue (congestion) or link failures that isolate node pairs. Various routing rules (algorithms) are stored at the nodes to continue communication, via alternate paths, when congestion and/or link failures occur. The combined effects of congestion and routing are difficult to analyze. This paper describes simulation programs for packet switching networks which model congestion, routing and link failures and the results of reliability studies performed using these programs. Simulation results are analyzed and some conclusions are drawn on how network reliability is affected by different congestion factors.