nt consumption is obtained for the case where the VoIP client did not activate VAD, which means that each UE was transmitting constantly at a rate of one packet every 20 ms regardless of the voice activity pattern. This kind of behaviour results in no practical opportunities for DRX sleep mode and higher power consumption. In the following cases, connected mode DRX is activated with different settings. DRX long cycle is fixed at 40 ms, but short cycle is changed between 20 and 20 ms DRX cycle 40 ms DRX cycle 20 ms 1 ms 40 ms Sleep mode Sleep mode between voice VoIP packets between voice VoIP packets packets packets Figure 16.30 Overview of VoLTE transmission and DRX Smartphone Optimization Power consumption DRX 20 ms / on 6 DRX 20 ms / on 6 DRX 40 ms / on 6 DRX 40 ms / on 4 No VAD Figure 16.31 DRX impact on VoLTE current consumption 40 ms. Additionally, the OnDuration, which is the time the UE remains active after waking up on every cycle, was changed between 6 and 4 ms. In the first case, with 20-ms short cycle and 6 ms on duration, the average current consump- tion was reduced by 20% compared to the reference case. Increasing the short cycle to 40 ms provided additional gains up to 27%. Finally reducing the OnDuration to 4 ms only provided small additional gain. During all the tests, the voice quality in terms of MOS was monitored, but the increase of the packet delay jitter caused by having 40 ms DRX cycles instead of 20 ms DRX cycles did not reflect on any appreciable MOS degradation during the call. Power Consumption with Integrated VoLTE Client Power consumption with VoLTE and other VoIP services depends highly on the UE and how efficiently the voice is handled by hardware and software implementation. While the expecta- tion is that VoLTE should provide similar or better power consumption than legacy 3G circuit switched voice to offer a good user experience, some terminals and early implementations of VoLTE may not achieve the required level of efficiency when using solutions which rely on UE application pr