 different results. Some operators start considering CSF after the SDCCH has been assigned not to consider SDCCH blocking. Others want to model the user's perception and to consider all types of failures. Handover Success Rate The HSR is defined as the percentage of successful outgoing handover attempts. The total number of attempts, failures and blockings on incoming and outgoing handovers are available either to cell-to-cell or BSC-to-BSC levels. High rates of outgoing HO failures explain high values of the DCR. Moreover, in the troubleshooting process, engineers can resort to other KPIs to analyse anomalies in more detail. Hereafter, the most relevant KPIs used in the troubleshooting mechanism are presented. TCH and SDCCH Availability Resources availability is the first mandatory requirement for communications to proceed. If the system does not offer enough physical or logical capacity to handle the demand this impacts on the perception of unsatisfied users. If queuing or directed re-try, for example, are activated, it may help to handle more TCH requests with less access failure rates. Radio Network Optimisation Traffic and Blocking In a cell with low traffic, DCR and CSF rates may appear outside objectives but a result of the low number of attempts in the denominator. Such cells have the lowest priority in optimisation because their impact is neglected. Alternatively, a cell with high traffic and high blocking encounters has CSF problems. This is explained through congestion, which generates TCH requests to be rejected. Timing Advance Cells with high timing advance are those taking communications far from the site. Due to weak coverage and path unbalance, it is normal to have high DCR and CSF values on such cells. In this case a solution can be obtained by changing and/or down-tilting the antenna, reducing power or limiting access by specific parameters. Path Balance Generally, due to high power and gain from the BTS side, downlink power is greater than that reached by uplink. Such path unbalance impacts an 