5.4.5 DRX (Discontinuous Reception) framework

The 5G System supports DRX architecture which allows Idle mode DRX cycle is negotiated between UE and the AMF. The Idle mode DRX cycle applies in CM-IDLE state and in CM-CONNECTED with RRC_INACTIVE state.

If the UE wants to use UE specific DRX parameters, the UE shall include its preferred values consistently in every Initial Registration and Mobility Registration procedure separately for NR/WB-EUTRA and NB-IoT. During Initial Registration and Mobility Registration procedures performed on NB-IoT cells, the normal 5GS procedures apply. For NB-IoT, the cell broadcasts an indication of support of UE specific DRX for NB-IoT in that cell and the UE can request UE specific DRX for NB-IoT in the Registration procedure irrespective of whether the cell broadcasts that support indication.

The AMF shall determine Accepted DRX parameters based on the received UE specific DRX parameters and the AMF should accept the UE requested values, but subject to operator policy the AMF may change the UE requested values.

The AMF shall respond to the UE with the Accepted DRX parameters separately for NR/WB-EUTRA and NB-IoT.

For details of DRX parameters, see TS 38.331 [28] and TS 36.331 [51].

The UE shall apply the DRX cycle broadcast in the cell by the RAN unless it has received Accepted DRX parameters for the RAT from the AMF and for NB-IoT the cell supports UE specific DRX for NB-IoT, in which case the UE shall apply either the DRX cycle broadcast in the cell or the Accepted DRX parameters for the RAT, as defined in TS 38.304 [50] and TS 36.304 [52].

The Periodic Registration procedure does not change the UE's DRX settings.

In CM-CONNECTED with RRC_INACTIVE state, the UE applies either the DRX cycle negotiated with AMF, or the DRX cycle broadcast by RAN or the UE specific DRX cycle configured by RAN, as defined in TS 38.300 [27] and TS 38.304 [50].