call. Typical mature networks with good coverage can have CSSR in the range 95-98%. Drive tests can be used to measure this KPI, but again network statistics give a more accurate picture. For packet-switched calls the equivalent of call set-up success rate is the 'PDP context activation success rate' which is applicable for 2G, 2.5G and 3G networks. It should be noted that the CSSR or PDP context activation success rates have to be adjusted for services purchased by the user. Typically many users do not purchase the packet call services but have phones capable of packet calls. Rejection of packet call requests from such users may form a high proportion of failures. In the circuit-switched call domain, pre- paid subscribers may be barred from certain services like roaming or international dialling by some operators. The effects of such failures need to be considered when calculating this KPI. Dropped Call Rate One characteristic of radio networks is a 'dropped call', which means the user experiences a termination of a call, which was not requested by either party in the call. Dropped calls can be due to coverage or due to interference and sometimes due to capacity. The number of dropped calls is measured by the system as network statistics and can be measured by drive testing to pinpoint the geographical location of the problem. Different operators measure dropped call rates differently. Some consider dropped calls as those calls which dropped after the conversation started. The logic is that the user is not normally charged until the conversation is started. However, some operators charge users from the instant they initiate signalling. For such operators the appropriate dropped call definition is any call that drops after the user has attempted to make a call. Mature 2G GSM networks can have dropped call rates of 1% for drops after the start of conversation and about 2% considering call set-ups. Call Quality Call quality measurements can be service-specific or independent of the service. 2G GSM systems provide a