Partitioning Customers into Service

We consider how to partition arriving customers into service groups that will be served separately , in a rst-come rst-served manner, by multi-server service systems having a provision for waiting, and how to assign an appropriate number of servers to each group. We assume that customers can be classiied upon arrival, possibly according to their service requirements. We model the congestion experienced by each server group as an M/G/s queue with unlimited waiting room. Even if the individual classes have exponential service-time distributions, it is important to consider non-exponential service-time distributions for the server groups to capture the variability eeect of partitioning when the mean service times diier among the customer classes. We use previously developed approximations for M/G/s performance measures to quickly evaluate alternative partitions. We thus provide methodology for studying the tradeoo between economies of scale associated with larger systems and the beneet of having customers with shorter service times separated from other customers with longer service times, as is done in service systems with express lines.