Multistage interconnection networks are used to connect processors to memories in shared memory multiprocessor systems. The performance evaluation of such networks is usually based on the assumption of a uniform memory reference pattern. Hot spots in such networks give rise to a nonuniform memory reference pattern and result in a degradation in performance. A comparison of the performance of unbuffered and buffered networks under a nonuniform traffic pattern is given. Analytical models have been developed for the evaluation of performance. An analytical model for unbuffered networks is developed in this paper, while the model for buffered networks is presented elsewhere. Results from the models are used to find the impact of different degrees of hot spot traffic and network size on the performance of the network. It is shown that an unbuffered network may perform better than a buffered network under a nonuniform traffic pattern. Finally, a hybrid mode network is suggested for optimum performance under different traffic conditions.