Section: 4.11.1.3.3A EPS to 5GS Idle mode mobility using N26 interface with data forwarding
Content: Figure 4.11.1.3.3A-1 describes the idle mode mobility registration procedure from EPS to 5GS when N26 is supported with data forwarding. Figure 4.11.1.3.3A-1: EPS to 5GS Idle mode mobility using N26 interface with data forwarding 1. Step 1-7 from clause 4.11.1.3.3 with the following enhancements: - In step 5b of the figure 4.11.1.3.3-1, if the old MME indicates Buffered DL Data Waiting in the Context Response (as specified in step 5 of clause 5.3.3.1A in TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [13]). - For Control Plane CIoT EPS Optimisation, when the DL data is buffered in old MME and the DL Data Expiration Time has not expired, the old MME shall discard the buffered DL data (as specified in step of clause 5.3.3.1A in TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [13]). 2. Steps 9-18 from clause 4.11.1.3.3 with following enhancements: In step 14a of the figure 4.11.1.3.3-1, the AMF forwards the Buffered DL Data Waiting indication from above to (V-)SMF in Nsmf_PDUSession_CreateSMContext service operation. If the Buffered DL Data Waiting indication is provided by AMF, the (V-)SMF and (V-)UPF shall allocate the user plane resource and include the N2 SM information (i.e. the V-CN Tunnel-Info) in the Nsmf_PDUSession_CreateSMContext Response towards the AMF in step 14d of the figure 4.11.1.3.3-1 to trigger the user plane setup in NG-RAN. NOTE: AMF may send NAS message Registration Accept in step 17 of figure 4.11-1.3.3-1 as part of the N2 message in step 3 below. 3. AMF to NG-RAN: N2 message (N2 MM information, N2 SM information list). If N2 SM information is received from SMF in step 2 above, the AMF sends a N2 request message to setup the user plane resource. NG-RAN performs RRC connection Reconfiguration with the UE to setup the user plane resource and response to AMF with N2 response message with N2 SM information. 4. Steps 11-13 from clause 4.11.1.2.2.2 with the following enhancement: Based on Buffered DL Data Waiting indication received in step 2 above, the (V-)SMF and (V-)UPF allocate data forwarding tunnel resource and provide the CN tunnel information for data forwarding from EPS (i.e. Forwarding F TEID) in Nsmf_PDUSession_UpdateSMContext Response to AMF in step 13 of figure 4.11.1.2.2.2-1. The (V-) SMF also starts a timer for release of resources for data forwarding. The (V-) SMF may select a different UPF from the serving (V-)UPF for data forwarding. The (V-)SMF shall not provide Charging Enforcement Rules and QoS Enforcement Rules to the (V-)UPF for DL packets that were received via the forwarding tunnel. 5. Steps 14-18 from clause 5.3.3.1A in TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [13] with following changes. The AMF sends the Context Acknowledge message to MME as in step 14 of figure 5.3.3.1A-1 in TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [13], including the CN tunnel information (i.e. Forwarding F TEID) for data forwarding from EPS received from (V-)SMF in step 4 above. The Serving GW forwards the buffered DL data to the (V-)UPF based on the Forwarding F-TEID received from MME. The data received by the (V-)UPF on the forwarding F-TEID is forwarded by the (V-)UPF on the (newly) established N3 tunnel to the NG-RAN. 6. SMF to UPF: N4 Session Termination/Modification. At the expiration of the timer started in step 4 above, the (V-) SMF starts the release of resource established in step 4 for data forwarding and informs the (V-)UPF.