st complete its scan of these five messages before it can lock on to the new channel and establish a TBF and then resume scanning for other adjacent cells in the BA list. Upon completion of the drive test and collecting and filtering through the measurement data, the TBF performance can be mapped out and overlaid with the application performance. The graphs in Figure 2.94 show an example of TBF performance from a single FTP download. In this example, there were no block errors since the test was done in ideal conditions (the RBB does not indicate any missing blocks). Radio Network Optimisation UL TBF Flow Control DL TBE Flow Control Log (RBB,2) Log(RI BB 2) SSN a nd RBB SSN and RBB Figure 2.94 Measured uplink and downlink TBF flow controls Nevertheless, the graph on the left clearly shows many short duration uplink TBFs while the right graph shows a single long TBF. Note how the starting sequence number (SSN) begins slowly, then rapidly repeats in a cyclical fashion until slowing down to the FAI. The above technique provides a practical way of visualising the TBF behaviour of EGPRS data sessions from a drive test analysis. It helps significantly with the understanding of how different application types impact and drive the EGPRS radio performance. Routing area updates and other GMM/SM can be mapped during the drive test analysis and the performance engineer can effectively utilise and apply the knowledge gained in this text to maximise and optimise the radio network performance of an EGPRS network. 2.9.3 Optimisation in the WCDMA Network Cluster Optimisation The optimisation process starts from the stage where initial network planning has finished. The network has been built - at least the majority of sites have been integrated. No users are in the network and the network does not carry any traffic. Therefore the optimisation has a target to guarantee the quality of basic services when they are launched The network is divided into geographical areas called clusters, each consisting of 10 to 20 sites. These geogra