ce Analysis Call Setup Time Call setup time is an important KPI, which measures the time it takes for a voice call to be established. In case of VoLTE this KPI can be measured from SIP signalling messages at the UE: from the instant the INVITE is sent from the calling party until the RINGING indication is received, as described in Figure 16.22. Figure 16.23 shows how VoLTE can significantly improve the call setup time compared to the legacy circuit switched systems. The total time for the call establishment depends on multiple factors such as whether the terminals were initially on RRC Idle or RRC Connected state when the call was originated. The laboratory measurements show VoLTE call setup time of 0.9- 2.2 seconds while the delay in the field is slightly higher depending on the operators' network and transport architecture. The corresponding typical 3G CS call setup time is 4 seconds and with CSFB in both ends approximately 6 seconds. Call setup time Idle-idle Idle-idle Connected- 3G idle-idle CSFB- (field) connected VoLTE CS voice Figure 16.23 Call setup time (VoLTE and CS Voice) Smartphone Optimization 3G CS VoLTE Figure 16.24 Mean opinion score (MOS) User Experience Benchmark Different tests were included in the benchmark. First, a 3G circuit switched mobile-to-mobile call using Adaptive Multirate Narrowband (AMR NB) 12.2 kbps codec was used as reference. One native client with AMR Wideband (AMR WB) 23.85 kbps codec was used to show the performance of VoLTE solution. AMR WB is widely known has High Definition (HD) voice. One third-party SIP client was used as representation of non-native clients. That client used two different codecs with Enhanced Full Rate Narrowband (EFR NB) and with AMR WB with variable rate. Finally, three different OTT applications with their own proprietary wideband codec implementation completed the list. Four metrics are shown in Figures 16.24, 16.26, 16.27 and 16.28 which include the following: Voice quality is a subjective metric which depends on multiple factors ranging from the s