= number of calls initiated on the cell Nbr Inc-HO = number of incoming handovers In this formula, incoming handovers are only considered because the successful outgoing handovers refer to TCHs that are normally released. Dropped call triggering starts logically after the called party answers the call. However, DCR for some operators starts to be calculated from the point where a TCH is assigned (before the communication phase). Another option is not to consider incoming handover attempts in the denominator, assuming that all successful incoming handovers resulted in successful outgoing handovers. Figure 2.58 presents the DCR calculation results according to two different formulas. Main KPIs The main concern for an operator in terms of voice quality is accessibility to the network and call quality (audio, drop call, handover). Those two aspects are directly related to revenue generated by voice traffic. Radio Network Planning and Optimisation Two different DCR formula results 3.50% 3.00% 2.50% 2.00% 1.50% 1.00% 0.50% 0.00% Formula_1 Formula Figure 2.58 DCR example according to various formulas In consequence, the main KPIs followed by operators are the call setup success rate (CSR) and the drop call rate (DCR). Occasionally, the handover success rate (HSR) may also be monitored. Drop Call Rate The DCR is logically defined as the ratio between the TCH drops occurring during the conversation phase to the number of successful seizures on the cell or area. Indeed, many definitions for the DCR exist according to the formula used to calculate it. Usage of a specific formula is operator/vendor dependent. Bad DCR performance can be due to capacity limitation, lack of coverage, interference, quality degradation, Call Success Rate or Call Setup Failure The CSR measures the ability of a cell/network to provide traffic channel to call originating mobiles. Any failure in the assignment phase is charged to the CSR. Here also results may vary according to what the operator wants to track. This means that different formulas give