4.11 User Plane CIoT EPS Optimisation

23.4013GPPGeneral Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) accessRelease 18TS

The User Plane CIoT EPS Optimisation functionality enables support for transfer of user plane data without the need for using the Service Request procedure to establish Access Stratum (AS) context in the serving eNodeB and UE.

If the following preconditions are met:

– UE and MME support User Plane CIOT EPS Optimisation as defined in clause 4.3.5.10,

– MME indicates "UE User Plane CIoT Support Indicator" IE to "supported" as defined in TS 36.413 [36],

– and the UE performs an initial connection establishment that establishes the AS bearers and the AS security context in the network and UE,

then the RRC connection can be suspended by means of a Connection Suspend Procedure (see clause 5.3.4A).

Based on trigger from the NAS layer when UE is in ECM-IDLE including if it attempts to send data using Control Plane CIoT EPS Optimisation as defined in clause 5.3.4B, the UE shall attempt the Connection Resume procedure, see clause 5.3.5A and TS 24.301 [46]. If the Connection Resume procedure fails, the UE initiates the pending NAS procedure, see TS 24.301 [46]. To maintain support for User Plane CIoT EPS Optimisation at UE mobility between cells configured on different eNodeBs, the AS Context should be transferred between the eNodeBs, see TS 36.300 [5] and TS 36.423 [76].

Early Data Transfer (EDT) for User Plane CIOT EPS Optimisation is defined in TS 36.300 [5] and clause 5.3.5A.

If the UE is in ECM-IDLE state with AS information stored, and the UE attempts to send data using Control Plane CIoT EPS Optimisation as defined in clause 5.3.4B, the UE shall attempt the Connection Resume procedure without Early Data Transfer.

By using the Connection Suspend procedure, see clause 5.3.5A and TS 36.300 [5]:

– the UE at transition into ECM-IDLE stores the AS information;

– the eNodeB stores the AS information, the S1AP association and the bearer context for that UE;

– MME stores the S1AP association and the bearer context for that UE and enters ECM-IDLE.

In the context of this functionality, the UE and the eNodeB store the relevant AS information at transition into ECM-IDLE.

By using the Connection Resume procedure, see clause 5.3.5A and TS 36.300 [5]:

– the UE resumes the connection with the network using the AS information stored during the Connection Suspend procedure;

– the, potentially new, eNodeB notifies the MME that the connection with the UE has been securely resumed and the MME enters ECM-CONNECTED.

If a MME has a S1AP association stored for a UE and the MME receives for that UE a EMM procedure over another UE-associated logical S1-connection or at Tracking Area Update procedure with MME change, or SGSN Context Request, when the UE has re-attached, or when the UE has been Detached, the MME and the previously involved eNodeB shall delete that stored S1AP association using the S1 Release procedure, see clause 5.3.5 and TS 36.413 [36].