the impact of moderate traffic on E-RAB setup success rate and RRC connection setup success rate. During highest peak of signalling traffic (RRC connection setup attempts increase to around four times the lowest level) the RRC connection setup success rate decreases significantly to 99.6% level but the E-RAB setup success rate decreases only RRC connection setup E-RAB setup success rate success rate Relative RRC connection setup attempts 100.0 Figure 12.21 Average RRC connection setup success rate, average E-RAB setup success rate and average relative RRC connection setup attempts in cluster during moderate traffic, 15 minutes statistics collection period LTE Small Cell Optimization marginally. Therefore, it can be said that in case the RRC setup success rate remains at high levels of 99.x% the E-RAB setup success rate does not suffer from increased inter-cell interference. Also in case of any admission control limitations (e.g. due to reaching the number of RRC-connected users capacity), the rejections already occur at RRC connection setup phase without any impact on E-RAB setup success rate. Based on the above, the CSSR calculated as RRC connection setup success rate X E-RAB setup success rate follows closely the RRC connection setup success rate. E-RAB setup success rate seldom decreases significantly as most of the failure scenarios are covered by the RRC connection setup success rate. E-RAB Drop The E-RAB drop rate defined as the number of abnormally released RBs leading to release of E-RAB divided by number of successfully setup RBs is correlated with the traffic and E-RAB setup attempts as can be seen from Figure 12.22. The setup success rates (random access, RRC connection and E-RAB) and E-RAB drop rate are having similar trend with traffic (inter-cell interference) increase. This is due to similarities between signalling procedures for setups and handovers and due to the fact that E-RAB drop rate is highly correlated with handover success rate (in this case intra-frequency handover success rate) as shown