REal-time delay estimation in call centers

We use computer simulation to study the performance of alternative real-time delay estimators in heavily loaded multiserver queueing models. These delay estimates may be used to make delay announcements in call centers and related service systems. We consider the classical delay estimator based on the queue length, QL_s, which multiplies the queue length plus one times the mean interval between successive service completions, ignoring customer abandonment. We show that QL_s has a superior performance in the GI/M/s model, but that there is a need to go beyond it in the GI/GI/s+GI model, allowing abandonment. To this end, we propose new, simple and effective, delay estimators based on the queue length. We also consider a delay estimator based on recent customer delay history in the system: the delay of the last customer to enter service, LES.