Section: 5.13 Discontinuous Reception and UE Specific DRX Parameter handling
Content: During the Attach and Tracking/Routing Area Update procedures in E-UTRAN, UTRAN and/or GERAN, the UE can signal its UE Specific DRX Parameters to the Core Network (MME in the E-UTRAN case and SGSN in UTRAN/GERAN case). In E-UTRAN and UTRAN, the UE may signal that it wishes to use the DRX cycle length broadcast in the RAN's System Information. Alternatively, the UE can propose a DRX cycle length separately for WB-EUTRA and NB-IoT. 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 during Attach and Tracking Area Update procedures irrespective of whether the cell broadcasts that support indication. The MME shall accept the value proposed by the UE for WB-E-UTRAN. For NB-IoT the MME should accept the UE requested value, but subject to operator policy the MME may change the UE requested values. The MME shall respond to the UE with the Accepted DRX parameter for NB-IoT. In each S1 interface Page Request message, the MME shall send the UE Specific DRX Parameters for the UE's current RAT (to help determine the DRX cycle length) and information derived from the IMSI (which defines when the UE will be awake from its sleep mode). Details are specified in TS 36.304[ Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) procedures in idle mode ]  [34]. NOTE 1: To ease backward compatibility with Pre-Release 8 SGSNs, the UTRAN and E-UTRAN DRX cycle lengths are encoded in the same field within the TS 24.008[ Mobile radio interface Layer 3 specification; Core network protocols; Stage 3 ]  [47] DRX parameter information element. At MME to MME, MME to SGSN and SGSN to MME mobility, the UE Specific DRX Parameters for RATs other than NB-IoT are sent from the old CN node to the new CN node as part of the MM context information and (except for NB-IoT) should not be sent by the UE in the Tracking Area Update message. NOTE 2: it is assumed that all SGSNs are Release 99 or newer and hence support storage of the Release '99 encoding of the TS 24.008[ Mobile radio interface Layer 3 specification; Core network protocols; Stage 3 ]  [47] DRX parameter information element. During Attach and non-periodic Tracking Area Update procedures on NB-IoT cells, the UE shall ensure that it has provided the MME with any UE Specific DRX parameter that applies to NB-IoT and optionally UE specific DRX parameter that applies for WB-E-UTRAN. If a CN node receives UE Specific DRX Parameters in a dedicated message from the UE (e.g. in a Tracking Area Update or Attach message), then the CN node updates any stored information with the information supplied by the UE and uses the UE provided information in preference to any information that might be received from another CN node during the same procedure. If the UE wishes to alter its GERAN or UTRAN/WB-E-UTRAN/NB-IoT UE Specific DRX Parameters while in E-UTRAN, then it shall send a Tracking Area Update Request message to the MME containing its new UE Specific DRX Parameters. If ISR had been activated for the UE, then the UE shall deactivate ISR by setting its TIN to "GUTI" so that the UE performs a Routing Area Update when it next enters GERAN/UTRAN coverage. When the UE performs that Routing Area Update, the SGSN will receive the updated DRX parameters within the MM context information sent by the MME and hence the UE should not include them again in the Routing Area Update Request message. If the UE wishes to alter its WB-E-UTRAN/UTRAN or GERAN DRX Parameters while in GERAN or UTRAN coverage, then the UE shall send a Routing Area Update Request message to the SGSN containing its new UE DRX Parameters. If ISR has been activated, the UE shall deactivate ISR by setting its TIN to "P-TMSI" so that the UE performs a Tracking Area Update when it next returns to E-UTRAN coverage. When the UE performs that Tracking Area Update, the MME will receive the updated DRX parameters (excluding the one for NB-IoT) within the MM context information sent by the SGSN and hence the UE should not include them again in the Tracking Area Update message. For NB-IoT, the UE shall apply the DRX cycle broadcast in the cell by the RAN unless it has received Accepted DRX parameters for NB-IoT from the MME and 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 NB-IoT, as defined in TS 36.304[ Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) procedures in idle mode ]  [34].