ranteed bit rate per RAB type is configured with the measured average user throughput for a certain traffic model on the ATM link layer including all the transport network layer overheads. average throughput is measured during the data transmission period within the duration of the AAL2 connection, as shown in Figure 5.5. The obtained average throughput depends on the peak data rate of the RAB as well as the applied traffic model. Table 5.1 gives an example of measured average link throughputs for various RABs. In this example, an ftp service of a mean file size of 25kbyte is given with different file size distributions. It can be seen that for the same mean file size, the measured average link throughputs (per user connection) using different file size distributions are similar with small deviations, and the value is larger for a higher RAB rate. If the applied traffic model changes, the measured average throughputs can be also different. It is suggested that before performing any network dimensioning, for a given traffic model, an average link throughput of a user connection should be measured for each RAB type to configure its corresponding CAC guaranteed bit rate. The setting of the CAC guaranteed bit rate can be also based on other optimization algorithms. The BRA and CTS functions are modeled only for the DCH transferring the packet switched traffic, mainly best effort and interactive traffic types. For modeling the BRA function, four parameters were implemented to decide an upgrade or downgrade of the RAB for a user connection, i.e. upgrade threshold, downgrade threshold, monitoring period and waiting time. Moreover, for upgrading the data rate, the CAC function is required to determine whether there are enough transport resources to support a higher data rate. The modeling of CTS requires defining an inactive timer to make a decision on when to switch off the DCH and move to the common channels, and applying the CAC function to check if there is enough transport resource for setting up a new AAL2 connecti