Loop Plant Modeling: Cost Models for Loop Plant Work Operations Using Semi-Markov Processes

An important consideration in making economic evaluations of proposed loop plant relief, rearrangement, and rehabilitation projects is the cost of loop plant work operations incurred to provide or maintain service. Such operations are performed by installers, cable maintenance and repair personnel, splicers, and support personnel including assignment and test bureau clerks, testers, frame personnel, and engineers. The traditional method of determining these costs is by direct measurement. Direct measurement is usually limited, however, to a fixed set of conditions whereas a model can show how the costs vary with changing conditions. Therefore, a model can be more useful in estimating the change in costs caused by altering current work procedures, for ex927 ample, or by introducing some new technology. Also, a model can be tailored to fit local conditions such as a high defective pair rate, for example. This article presents a method for obtaining cost distributions of loop plant work operations as a function of plant conditions such as record error rates and defective pair rates. The method views a work operation, such as a cable pair transfer or the completion of an inward service order, as a semi-Markov process with constant state delay times and an absorbing state corresponding to the completing step of the operation. The states of the process correspond to activities performed during the work operation. The constant state delay times, i.e., the times required to perform the activities, are defined to be the costs of the activities.