Section: 5.3.4B.4 Establishment of S1-U bearer during Data Transport in Control Plane CIoT EPS Optimisation
Content: Figure 5.3.4B.4-1: Establishment of S1-U bearer during Data Transport in Control Plane CIoT EPS Optimisation UE or MME can use this procedure if the UE and MME successfully negotiate S1-U data transfer or User Plane CIoT EPS Optimisation in addition to Control Plane CIoT EPS Optimisation based on the Preferred and Supported Network Behaviour as defined in clause 4.3.5.10. The MME either because it has received the NAS message as defined in steps 2-3 or the MME decides that S1-U based data transfer is now preferred e.g. determined by the size of data transferred in UL and DL using Control Plane CIoT EPS Optimisation triggers the establishment of S1-U bearer(s). The MME checks if the UE can support the establishment of required number of additional user plane radio bearers based on the maximum number of user plane radio bearers indicated by UE in the UE Network Capability IE as defined in clause 5.11.3. If the MME takes the decision that S1-U data transfer is now preferred steps 2-3 are not needed. 1. UE is sending and receiving data in NAS PDUs using the Control Plane CIoT EPS Optimisation. 2. The UE may be triggered to establish user plane bearers and sends a Control Plane Service Request with an active flag towards the MME encapsulated in an RRC message to the eNodeB. The RRC message and this NAS message are described in TS 36.300[ Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 ]  [5] and TS 24.301[ Non-Access-Stratum (NAS) protocol for Evolved Packet System (EPS); Stage 3 ]  [46] respectively. 3. The eNodeB forwards the Control Plane Service Request with active flag to MME. NAS message is encapsulated in an S1-AP UL NAS Transport Message (NAS message, TAI+ECGI of the serving cell, S-TMSI, CSG ID, CSG access Mode). Details of this step are described in TS 36.300[ Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 ]  [5]. If the MME receives the Control Plane Service Request with active flag defined in steps 2-3 it shall establish S1-U bearer(s) and execute the transfer. If the MME cannot handle the procedure associated to the Control Plane Service Request with active flag, it shall reject it. CSG ID is provided if the UE sends the NAS message via a CSG cell or a hybrid cell. CSG access mode is provided if the UE sends the NAS message via a hybrid cell. If the CSG access mode is not provided but the CSG ID is provided, the MME shall consider the cell as a CSG cell.If a CSG ID is indicated and CSG access mode is not provided, and there is no subscription data for this CSG ID and associated PLMN or the CSG subscription is expired, the MME rejects the Control Plane Service Request with an appropriate cause. The UE shall remove the CSG ID and associated PLMN of the cell where the UE has initiated the service request procedure from the Allowed CSG list, if present. 4. The MME shall send any remaining UL data over S11-U and in order to minimize the possible occurrence of out of order DL data e.g. caused by earlier DL data which were sent on the Control Plane may send a Release Access Bearers Request message to the Serving GW that requests the release of all S11-U bearers for the UE. The MME locally deletes any existing ROHC context used for Control Plane CIoT EPS Optimisation, and other S11-U related information in UE context, including TEID (DL) for the S11-U, etc, but not the Header Compression Configuration. NOTE: The MME may use the "Delay Downlink Packet Notification Request" causing the Serving GW to not send Downlink Data Notifications as described in clause 5.3.4.2 to minimize the impact of possible Downlink Data Notifications this step may cause. 5. If the Serving GW receives the Release Access Bearers Request message it releases all MME related information (address and downlink TEIDs) for the UE and responds with a Release Access Bearers Response message to the MME. Other elements of the UE's Serving GW context are not affected. If downlink packets arrive for the UE, the Serving GW starts buffering downlink packets received for the UE and initiating the "Network Triggered Service Request" procedure, described in clause 5.3.4.3. 6. The MME sends S1-AP Initial Context Setup Request (Serving GW address, S1-TEID(s) (UL), EPS Bearer QoS(s), Security Context, MME Signalling Connection Id, Handover Restriction List, CSG Membership Indication, Service Accept) message to the eNodeB for all PDN connections that MME has not included Control Plane Only Indicator in ESM request. The MME responds to the UE with a Service Accept message. The eNodeB stores the Security Context, MME Signalling Connection Id, EPS Bearer QoS(s) and S1-TEID(s) in the UE RAN context. The step is described in detail in TS 36.300[ Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 ]  [5]. Handover Restriction List is described in clause 4.3.5.7 "Mobility Restrictions". 7. If the Control Plane Service Request is performed via a hybrid cell, CSG Membership Indication indicating whether the UE is a CSG member shall be included in the S1-AP message from the MME to the RAN. Based on this information, the RAN can perform differentiated treatment for CSG and non-CSG members. The eNodeB performs the radio bearer establishment procedure. The user plane security is established at this step, which is described in detail in TS 36.300[ Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 ]  [5]. The UE needs to locally delete any existing ROHC context used for Control Plane CIoT EPS Optimisation. When the user plane radio bearers are setup, EPS bearer state synchronization is performed between the UE and the network, i.e. the UE shall locally remove any EPS bearer for which the MME has not included Control Plane Only Indicator in ESM request and for which no radio bearers are setup. If the radio bearer for a default EPS bearer is not established, the UE shall locally deactivate all EPS bearers associated to that default EPS bearer. 8. As the user plane radio bearers are setup the UE shall use user plane bearers to transfer data PDUs, except for EPS bearers the MME has included Control Plane Only Indicator in ESM request and for which Control Plane CIoT EPS Optimisation is still be used. The uplink data from the UE can now be forwarded by eNodeB to the Serving GW. The eNodeB sends the uplink data to the Serving GW address and TEID provided in the step 6. The Serving GW forwards the uplink data to the PDN GW. 9. The eNodeB sends an S1-AP message Initial Context Setup Complete (eNodeB address, List of accepted EPS bearers, List of rejected EPS bearers, S1 TEID(s) (DL)) to the MME. This step is described in detail in TS 36.300[ Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 ]  [5]. 10. The MME sends a Modify Bearer Request message (eNodeB address, S1 TEID(s) (DL) for the accepted EPS bearers, Delay Downlink Packet Notification Request, RAT Type) per PDN connection to the Serving GW. If the Serving GW supports Modify Access Bearers Request procedure and if there is no need for the Serving GW to send the signalling to the PDN GW, the MME may send Modify Access Bearer Request (eNodeB address(es) and TEIDs for downlink user plane for the accepted EPS bearers, Delay Downlink Packet Notification Request) per UE to the Serving GW to optimise the signalling. The Serving GW is now able to transmit downlink data towards the UE. 11. The Serving GW shall return a Modify Bearer Response (Serving GW address and TEID for uplink traffic) to the MME as a response to a Modify Bearer Request message, or a Modify Access Bearers Response (Serving GW address and TEID for uplink traffic) as a response to a Modify Access Bearers Request message. If the Serving GW cannot serve the MME Request in the Modify Access Bearers Request message without S5/S8 signalling other than to unpause charging in the PDN GW or without corresponding Gxc signalling when PMIP is used over the S5/S8 interface, it shall respond to the MME with indicating that the modifications are not limited to S1-U bearers, and the MME shall repeat its request using a Modify Bearer Request message per PDN connection.