SUMMARY
This paper is a detailed analysis of traffic in public switched telephone network or system (PSTN). Using Nigerian telecommunications (NITEL) as case study for the month of February, 2005. A comprehensive evaluation of traffic congestion along three routes were analyzed i.e. Abuja to Kaduna, Abuja to bauchi, Abuja to Benin during the busy hour in relation to availability dimensioning, lost call, call completion ratio, erlang, and grade of service was carried out. In view of this an insight was given into the types and forms of switching signaling and the type of switching equipment majorly used by Nigerian telecommunication (NITEL). Based on the data and physical observation it was seen that the performance of an exchange is been determined by the grade of service (probability of meeting congestion) the lower the grade of service, the lower the blocked calls. The call completion ratio increases with decrease in grade of service. The higher the call completion ratio of an exchange the lower the grade of service.