We consider a network of N nodes with given distances in which customers arrive at one of the nodes and request transportation to one of the other nodes. There is a finite number of servers (or transporters) with possibly different capacities and speed available. We show that there exists a critical arrival rate κc, such that if the arrival rate is larger than κc then the number of customers in the system increases to infinity; with linear speed no matter which routing strategy for the transporters is chosen (even if we allow the strategy to depend on the future arrival process). If, on the other hand, κ < κc then there exists even a fixed periodic routing strategy which keeps the system stable (in a sense to be made precise). We prefer to start with a deterministic set-up which allows very general arrival processes and look at the stochastic case only in the final section where we get more refined results by assuming that the arrival process has integrable stationary ergodic increments (which still allows batch arrivals and long-range dependence). Potential applications include the control of elevators in highrise buildings.
