When a relief toll switching system is used to alleviate the exhaust problem of an existing toll switching system of the same generic, type, a rehoming program (specifying amounts and timings of trunk rearrangements) is dictated primarily by the ratio of the monetary discount rate to the traffic growth rate. If this ratio is greater than unity, the rehoming strategy calls for a conservative program of restraint whereas if this ratio is smaller than unity, the rehoming strategy adopts an aggressive program of activity. When the relief and the existing switching systems are not of the same type, the lower trunk maintenance expenses on the relief switching system provide an impetus to rehome more existing trunks onto the relief switching system. It is found that this stimulation of early deloading affects the rehoming strategies significantly. Depending on the amount of stimulation involved, a conservative rehoming program could be changed to a moderate and even an aggressive one.

When an existing toll machine exhausts and a relief toll machine is added, rehoming of existing trunk groups is necessary. The intent of this paper is to determine rehoming programs whereby the present worth of the total trunk rearrangement cost is minimized while the total number of trunks to be rearranged at any stage of the program is constrained to lie within specified lower and upper limits. The rehoming program will specify the amounts of trunks to be rearranged and their corresponding timings for the rearrangements to take place. It is found that the choice of a proper rehoming strategy is critically dependent on the relative magnitude of the monetary discount rate compared to the traffic growth rate. When the discount rate matches the growth rate, any feasible rehoming strategy for any type of existing and relief machines is appropriate. If the discount rate is lower than the growth rate, it is more economical to rehome the maximum allowable amount of trunks as early as possible. On the other hand, if the discount rate is higher than the growth rate, the rehoming strategy is completely reversed. This case calls for a delay of as much rehoming as possible. However, the number of trunks to be rearranged during each stage of the rehoming program is bounded by the specified minimum allowable limit.

In order to investigate overload control strategies for large electronic switching systems (ESS), it is extremely valuable to be able to load test actual switching machines in a controlled laboratory environment. This method is superior when compared to both testing actual machines in service (where service deterioration cannot be tolerated) and simulating test of virtual machines (where sufficient realism may not be attainable). In the past, this form of experimentation has not been feasible for large ESS's because of both technical and economic problems associated with existing methods of generating the high volume of traffic required for overload testing. With the advent of the real-time traffic simulator known as the programmed electronic traffic simulator (PETS), however, it has become practical to conduct real-time tests of on-line overload control systems. PETS has been utilized to perform overload control experiments on an ESS to demonstrate the feasibility of conducting controlledenvironment overload testing on an actual ESS. It is the intent of this paper to describe the methodology used in the simulation experiments conducted and summarize some of the simulation results. In particular, the results of the three overload control systems will be compared with respect to both the total number of calls completed within a specified period of time and the grade of service provided. The sensitivity of system performance to the peakedness factor of the offered traffic will also be presented.