nterference and therefore when traffic grows and inter-cell interference grows parameter optimization becomes essential. The RRC setup success rate optimization also RRC connection setup success rate (%) Figure 12.16 RRC connection setup success rate improvement after parameter optimization in coverage-limited cluster, day-level statistics LTE Key Performance Indicator Optimization 100.0% 99.5% 99.0% 98.5% 98.0% 97.5% 97.0% 96.5% 96.0% 95.5% 95.0% Random access setup success rate Figure 12.17 Random access setup success rate versus RRC connection setup success rate in a cluster during moderate traffic, 15 minutes statistics collection period improved the random access success rate, that is, the improvements after day 5 in Figure 12.16 are also visible as an improvement in Figure 12.12 after day 45. This is caused by the less amount of repetitions of preambles due to message 4 problems and less amount of RRC connection setup attempt procedures due to the improved RRC connection setup complete detection. 12.4.3 E-RAB Setup After successful RRC connection setup procedure the call setup continues with the E-RAB setup procedure as shown in Figure 12.8. The E-RAB setup success rate itself can be defined based on network statistics from eNodeB point of view: Number of initial context setup response messages (S1 application protocol) sent by the eNodeB to the mobility management entity (MME) divided by number of initial context setup request (S1 application protocol) sent by MME to the eNodeB or Number of E-RAB setup response messages (S1 application protocol) sent by the eNodeB to the MME divided by number of E-RAB setup request messages (S1 application protocol) sent by MME to the eNodeB. As shown in Figures 12.8 and 12.18, the E-RAB setup covers radio bearer (RB) setup between the UE and the eNodeB and the S1 bearer setup for the UE between eNodeB and the evolved packet core (EPC) serving gateway (S-GW). It should be noted that here the E-RAB setup success rate analysis contains only the RB setup part, that is, S1 bea