 deployment strategy. The number of VoLTE calls generated per single UE per day is just tens whereas the number of non-GBR E-RABs is several hundreds and therefore the VoLTE share from all E-RABs will be small even in case each UE would generate some VoLTE calls per day. LTE Small Cell Optimization LTE eNB SGW, PGW Access Evolved Control packet Figure 14.11 VoLTE system architecture The share of QCI1 E-RAB setup attempts from all E-RAB setup attempts, containing QCI1 and non-guaranteed bitrate QCIs, is below 1% but rapidly increasing in case of example networks 1 and 3 which means quick transformation from CSFB to VoLTE. For example network 2 the main voice call method is still CSFB utilizing the existing 3G network as much as possible. Setup Success Rate The QCI1 E-RAB setup success rate shown in Figure 14.13 is the radio network statistics measurement of VoLTE setup success rate. It covers the E-RAB setup portion of the whole VoLTE setup signalling shown in Figure 14.14. The QCI5 E-RAB carries all the session initiation protocol (SIP) signalling and the QCI1 E-RAB then carries the actual voice user plane data. More details on the SIP signalling for VoLTE call setup can be found from [3]. The QCI5 E-RAB is setup at the time the terminal is attached to the network and SIP signalling registration to IMS is then done using QCI5 E-RAB. Example 1 Example 2 Example 3 0.80% 0.70% 0.60% 0.50% 0.40% 0.30% 0.20% 0.10% 0.00% Figure 14.12 QCI1 E-RAB setup attempts share from all E-RAB setup attempts VoLTE Optimization Example 1 QCI1 Example 2 QCI1 Example 1 all QCIs Example 2 all QCIs 100.00 99.95 99.90 99.85 99.80 99.75 99.70 99.65 99.60 99.55 99.50 99.45 Figure 14.13 E-RAB setup success rate for QCI1 and all QCIs Originating UE IMS network Terminating UE Initiate INVITE 100 Trying INVITE 100 Trying 183 Session Progress EPS bearer activation for QCI1 and audio video path setup 183 Session Progress PRACK EPS bearer activation for QCI1 and audio video path setup PRACK 200 OK 200 OK UPDATE UPDATE 200 OK 200 OK 180 Ringing 180