The IP based transport of real time services like for example of speech and moving pictures in mobile networks is considered as an utmost promising application of third generation wireless networks (UMTS). An essential condition for offering these services in satisfactory quality is a functioning admission control. Aim of the admission control is to reject service requests if their acceptance could lead to an overload of the transport system.

The following admission control strategy is a simple and effective overflow defense mechanism: A new arriving request is accepted by the network node if and only if the actual packet arrival rate - generated by the just active requests - is not greater than some threshold. However, also if this threshold is less than the processor capacity, buffer overflow may occur due to the on-off structure of the requests. Therefore token bucket algorithms are often used for preventing overload for the processors handling the packets. The probability of packet loss and the probability of a non accepted request depending on the threshold value are of interest.