ecrease of the average throughput) for traffic class i due to link congestion as a resultant of the total load of all traffic classes. It can be obviously seen that the delay factor depends on the bearer type of the traffic class. As introduced in section 6.3.6, the basic M/G/R-PS model is extended to consider the impact of TCP slow-start. And further improvements are proposed in section 6.3.7.1 to add the extra delay caused by TCP connection setup and termination, and replace the constant RTT with a varying RTT which is a function of link congestion. Based on these extensions, the general form of the basic M/G/R-PS model (6.32) is expanded to (6.33). It is a general form of the improved M/G/R-PS model, which is used to approximate the average transfer delay for traffic class i in this multiple traffic classes scenario: x<xxlow-start_i (6.33) x x x stow-start_i an approximation of the estimated RTT as a function of link congestion. It is noticed that Xslow-start_i is also RAB specific. Moreover, by adding the extra delay for setting up and releasing the TCP connection, the expected file transfer delay E{T(xi)}* is calculated with (6.34). (6.34) 6.3.7.4 Extension for case with BRA and not Applying CAC This section extends the M/G/R-PS model for the scenarios of applying the Bit Rate Adaptation (BRA) function for the transport in the UTRAN. As introduced in section 3.3.4.3, BRA is one of the UMTS resource management function dedicated for the packet-switched data traffic. It is used to dynamically change the peak data rate of a user connection during its data transfer process. The data rate adaptation is carried out by performing RAB upgrades to 6.3 Dimensioning for Elastic Traffic increase data rate and RAB downgrades to decrease data rate. The adaptation of data rate per flow is determined by the activity of the user connection as well as the available network resources. As a result, the peak data rate of elastic traffic flows is not a constant value, and thereby the M/G/R-PS model cannot be directly applied. The