Actually, oversubscritption should generally considered good. For example, in the Public Switched Telephone Network (PSTN), if we designed it such that there was no oversubscritption, every phone would have wires connected to every other phone. Obviously this does not happen so we design for a certain amount of call blocking. We have all experienced the "All circuits are busy" message. How much blocking should we design for? What is the science of design networks for oversubscritption?