Abstract In this paper a large common user network for data communications is investigated in an operational environment where about half the traffic was in the form of short messages and the other half was in the form of long ones, where short messages carry the implicit requirement to transit the network with very short time delays. A number of hypothetical networks were designed for the purpose of comparing circuit and packet switching technologies with respect to efficiency, cost, and throughput. The sensitivity of the results to certain assumptions and certain parameters of network performance were also examined in order to make the results applicable over a broad range of interest. Under the assumptions of this study, packet switched implementations showed decided advantages over circuit switched implementation, as measured by transmission utilization efficiencies and overall network costs.