 the mobile must analyze the PDCCH physical channel, which allows it Radio Interface Procedures to avoid processing this channel every millisecond and in this way to preserve the consumption of its battery (Figure 4.11). shortDRX-Cycle onDurationTimer longDRX-Cycle onDurationTimer drx-InactivityTimer drxShortCycleTimer Figure 4.11. DRX function For a color version of the figure, see www.iste.co.uk/perez/volte.zip An inactivity timer drx-Inactivity Timer of the DRX function is triggered when the mobile receives data on the PDCCH physical channel. This timer is reinitialized each time that the mobile receives data on the PDCCH physical channel. When the timer drx-Inactivity Timer expires, the mobile starts an optional period for the short cycle corresponding to the timer drxShort Cycle Timer. During the short cycle, the mobile analyzes the PDCCH physical channel in a duration corresponding to the timer onDurationTimer. During the short cycle, the triggering of the active period is provided by the following formula: [(SFN * 10) + (sub-frame number)] modulo (shortDRX-Cycle) = (drxStartOffset) modulo (shortDRX-Cycle) When the timer drxShort Cycle Timer expires, the mobile starts the long cycle period for which the triggering of the active period is provided by the following formula: [(SFN * 10) + (sub-frame number)] modulo (longDRX-Cycle) = drxStartOffset The parameter configuration of the DRX function is indicated in the RRC messages of establishment or re-establishment of the connection. VoLTE and ViLTE The eNB entity indicates the activation of the DRX function while using the DRX control element in the MAC frame. The timer drx-Retransmission Timer defines an inactive period of the DRX function during an expected HARQ retransmission. The timer drx-Retransmission Timer starts after the round trip HARQ timer associated with the HARQ retransmission. 4.2.2.3. SPS function The semi-persistent scheduling (SPS) function is applied to the applications that have a periodic character, for example the voice which produces a b