These reports and statistics help in segregating faulty situations and faulty parts of the network, which can be separated from the rest of the network for detailed trouble shooting. For example, counters can portray a picture where a certain area of the network is having a lot of call drops. Based on this report either a drive test team can be sent to check the real performance or a BTS engineer can be summoned for checking alarms and faulty signals coming from the BTS serving that area. In this way, before the customers really start to call the customer service lines and complain, the operator can take preventive action and take advantage of the remote health checks performed manually or via some special tools. These tools are customised, as per the key performance indicators chosen by the operator, to select the criteria used for measuring performance. On selection of the criteria, thresholds are set for the tool to function and finally corrective actions are taken that can be triggered automatically or manually. Such tools can be simple Java based programs running on typical window based laptops or they can be complex automated ones based on Unix machines. They have user friendly graphical user interfaces, easily connected to the network by means of LAN cables as they interface with the IP based backbone network running throughout the network, on top of their backbone networks. Remote health checks are an excellent way of ensuring network stability and keeping the load of the network operation and maintenance personnel low. They help to keep high levels of network performance by proactively searching for malfunctions, bugs and alarms in the system and by timely detection, which prevents problems from turning into potential troubles. At the end of the day the checks provide a healthy system that helps to produce optimum performance from the network, thus keeping customers happy and satisfied. Appendix B HSDPA Rafael Sánchez-Mejías This appendix provides a brief introduction to high speed downlink packet access