Using different response-time requirements to smooth time-varying demand for service

Many service systems have demand that varies significantly by time of day, making it costly to provide sufficient capacity to be able to respond very quickly to each service request. Fortunately, however, different service re quests often have very different response-time requirements. Some service r equests may need immediate response, while others can tolerate substantial delays. Thus it is often possible to smooth demand by partitioning the serv ice requests into separate priority classes according to their response-tim e requirements. Classes with more stringent performance requirements are gi ven higher priority for service. Lower capacity may be required if lower-pr iority-class demand can be met during off-peak periods. We show how the pri ority classes can be defined and the resulting required fixed capacity can be determined, directly accounting for the time-dependent behavior. For thi s purpose, we exploit relatively simple analytical models, in particular, M -t/G/infinity and deterministic offered-load models. The analysis also prov ides an estimate of the capacity savings that can be obtained from partitio ning time-varying demand into priority classes. (C) 1999 Published by Elsev ier Science B.V. All rights reserved.