th elastic traffic and circuit-switched traffic. This section investigates such a scenario as shown in Figure 6.23. The circuit-switched traffic, 6 Dimensioning for Single ATM-Based lub which is generated by real-time critical applications with strict QoS requirements, is subject to connection admission control (CAC) function to guarantee its QoS requirement. However, for elastic traffic no CAC is applied. And at the network level, the circuit-switched traffic is given a higher priority for transmission over the elastic traffic, with a strict priority scheduling scheme. In order to determine the application performance of elastic traffic, the consequence of strict priority scheduling and the possible multiplexing gain due to capacity sharing between the two traffic types have to be considered. In the following, an approximation method is suggested to estimate the achievable application QoS for elastic traffic in case of sharing the lub link with the circuit-switched traffic. Rejected connections circuit-switched type of traffic Pelastic elastic traffic Figure 6.23: Elastic traffic shares the lub link with circuit-switched traffic Let Lcs denote the mean carried load of the circuit-switched traffic after the CAC function, and Lelastic denote the mean traffic load of the elastic traffic. Given the total lub link capacity C lub, the mean bandwidth Celastic that can be utilized by the elastic traffic in average can be estimated with equation (6.37). Because of the elastic property of TCP, the elastic traffic intends to utilize any available bandwidth on the link. As a result of the priority scheduling, any bandwidth which is not used by the circuit-switched traffic can be taken by the elastic traffic. Thus it can be assumed that in average the elastic traffic can use the bandwidth up to (C lub - Lcs ) In this way, it is assumed that there is a complete bandwidth sharing between the two traffic types and thus has the possibility of achieving a high utilization. Celastic (6.37) With Celastic, a normalized elastic traff