Section: 4.3.22 UE Power Saving Mode
Content: A UE may adopt a PSM that is described in TS 23.682[ Architecture enhancements to facilitate communications with packet data networks and applications ]  [74]. If a UE is capable of adopting a PSM and it wants to use the PSM it shall request an Active Time value and may request a Periodic TAU/RAU Timer value during every Attach and TAU procedures, which are handled as described in TS 23.682[ Architecture enhancements to facilitate communications with packet data networks and applications ]  [74]. The UE shall not request a Periodic TAU/RAU Timer value if it is not requesting an Active Time value. The network shall not allocate an Active Time value if the UE has not requested it. PSM has no support in the CS domain on the network side. NOTE 1: When the PSM is activated the UE might not be available for paging of Mobile Terminated CS services even though the UE is registered in the CS domain. NOTE 2: The Attach and TAU procedures of this specification are not showing the details of the Periodic TAU Time and Active Time negotiation, i.e. are not showing the related IEs. If the network allocates an Active Time value, the UE and the MME starts the Active timer (see clause 4.3.5.2) with the Active Time value allocated by the network when transitioning from ECM_CONNECTED to ECM_IDLE. The UE shall stop the Active timer, if running, when a transition to ECM_CONNECTED mode is made. When the Active timer expires, the UE deactivates its Access Stratrum functions and enters PSM. In PSM, due to deactivation of Access Stratum functions, the UE stops all idle mode procedures, but continues to run any NAS timers that may apply, e.g. the periodic TAU timer. The UE shall resume Access Stratum functions and idle mode procedures before the periodic TAU timer expires for performing the periodic TAU procedure as applicable. The UE may resume idle mode procedures and Access Stratum functions any time while in PSM, e.g. for mobile originated communications. Any timers and conditions that remain valid during power-off, e.g. for NAS-level back-off, apply in the same way during PSM. When the Active timer expires for the UE, the MME knows that the UE entered PSM and is not available for paging. The MME handles availability for paging as detailed in clause 4.3.5.2. On UE side the PSM complies with some substates of EMM_REGISTERED, as specified in TS 24.301[ Non-Access-Stratum (NAS) protocol for Evolved Packet System (EPS); Stage 3 ]  [46]. The MME considers the UE to be EMM_REGISTERED, but not reachable. The UE's Access Stratum functions are considered as deactivated during PSM. For mobile terminated data while a UE is in PSM, the functions for High latency communication may be used as described in clause 4.3.17.7. When the UE has bearers for emergency services, the UE shall not apply PSM. When the UE is attached for RLOS services, the UE shall not apply PSM.