A Note on Approximating Peak Congestion in Mt/G/\infty Queues with Sinusoidal Arrivals

We study the M_t /G/\infty queue where customers arrive according to a sinusoidal function \lambda _t = \lambda + A sin(2\pi t/T) and the service rate is \mu . We show that the expected number of customers in the system during peak congestion can be closely approximated by (\lambda + A)/\mu for service distributions with coefficient of variation between 0 and 1. Motivated by a result derived by Eick, Massey, and Whitt that the time lag of the peak congestion from the peak of the customer arrivals is 1/2\mu for models with deterministic service times, we show that the time lag for exponential service times is closely approximated by 1/\mu . Based on a cycle length of 24 hours and regardless of the values of other system parameters, these approximations are of the order of 1% accuracy for \mu = 1, and the accuracy increases rapidly with increasing \mu .