Add to ORKGIn this paper a numerical analysis is presented, dealing with an advance reservation communication system whith preemption. The duration of reservations are assumed to be geomatrically distributed and is unknown at the beginning of the reservation, as it is the case in on-demand systems. Performance parameters are computed for that model and discussed in view of ongoing work of a suitable admission control. Results gained by the model are compared with those of a simulation model where durations are known, showing that the performance of both models differs only slightly. A pure advance reservation system and a fully shared system using immediate and advance reservation are studied. All considerations made in this paper are limited to a sin...