onnections N, the blocking probability under the link bandwidth C can be calculated with the Erlang-B formula (6.6). When the network consists of multiple traffic streams, the model is generalized to the multi-dimensional Erlang-B formula. In the concept of dimensioning, the link bandwidth C should to be numerically derived with the Erlang-B formula such that a desired blocking probability (e.g. 1%) is achieved. 6.2.4 Validation of Erlang Model This section validates the Erlang-B formula (equation (6.6)) for dimensioning of streaming traffic for a guaranteed blocking probability, in the following called CAC reject ratio, through simulations. The employed CAC (Call Admission Control) function in the lub transport network has been explained in section 3.3.4.3. As the Erlang-B formula is applied for the single traffic stream scenario, thus only one stream service is selected for the simulations. Voice is a typical circuit-switched type of traffic. The voice traffic model is given in Table 5.2. For call admission control, the required bandwidth for each voice connection is set to 12.4 kbps on the lub interface (at the ATM level). The validation of the Erlang-B formula consists of three parts: firstly the Erlang-B formula (6.6) is used to estimate the CAC reject ratio of the voice traffic given different offered traffic, and furthermore equation (6.8) and (6.9) are applied to calculate the obtained link utilization; secondly, the derivation of the state probabilities given in equation (6.5) is validated, and as well the insensitivity of the Erlang-B formula to the service time distributions is investigated; at last a group of dimensioning results for achieving certain guaranteed CAC reject ratio are presented, and the simulation results are compared against the calculations derived by Erlang-B formula. Figure 6.8 shows the calculated CAC reject ratio (left chart) and link utilization (right chart) over various offered voice traffic (in kbps) with Erlang-B formula. The calculated results are compared with the simulated