An order-based method for robust queue inference with stochastic arrival and departure times.

•The order-based method estimates the number of servers in unobservable GI/G/c queues.•This estimator is a lower bound and converges to the true number of servers.•In FCFS queues, this estimator has low error for small samples and converges quickly.•This estimator is robust to measurement error in arrival and departure times.