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No. 4 ESS is a newly developed, high capacity toll switching machine with a maximum of 107,000 4-wire terminations. Call switching is accomplished via a large digital time-division switching network. The network was evaluated both by a full scale simulation study and by analytical methods to determine its performance characteristics, that is, its blocking and switching capacity. In both simulation and analysis the network was modeled in its real environment, accounting for the effects of the path-hunt strategy. Results of the two methods are in close agreement. They show that the network can switch 47,000 Erlangs of traffic with a probability of blocking a connection on first trial of 0.005.