Section: 4.23.9.4 Simultaneous change of Branching Point or UL CL and additional PSA controlled by I-SMF
Content: This clause describes simultaneous change of UL-CL/BP function and additional PSA, e.g. addition of a new UL CL/BP and PDU Session Anchor (i.e. PSA2) and release of the existing UL CL/BP and additional PDU Session Anchor (i.e. PSA0), with target UPF(s) and source UPF(s) are all controlled by I-SMF. This procedure may be triggered after N2 handover or Xn based handover procedure. Figure 4.23.9.4-1: Simultaneous change of Branching Point or UL CL and additional PSA controlled by I-SMF Comparing to the clause 4.23.9.3, this procedure in addition changes the source UL-CL/BP by a target UL-CL/BP. 1-2. These steps are the same steps 1-2 in clause 4.23.9.3. 3. The I-SMF selects a UPF and using N4 establishes the target UL CL or BP of the PDU Session. 4. The I-SMF invokes Nsmf_PDUSession_Update Request (Indication of Change of traffic offload, (new allocated IPv6 prefix @PSA2, DNAI(s) supported by PSA2), (Removal of IPv6 prefix @PSA0, DNAI(s) supported by PSA0), DL Tunnel Info of the new UL CL/Branching Point) to SMF. The DL Tunnel Info of target UL CL/Branching Point is provided to SMF. 5. The SMF updates the remote PSA (PSA1) via N4 with the DL Tunnel Info of the Target UL CL/BP for the downlink traffic. 6-8. These steps are the same as steps 4-6 in clause 4.23.9.3. If EAS session continuity upon UL CL relocation is required, in step 7 the SMF provides the I-SMF additionally with an indication that a N9 forwarding tunnel to support the EAS session continuity is required, UL traffic filter for N9 forwarding by the target UL CL and the value of the timer to detect the end of activity on the N9 forwarding tunnel to support the EAS session continuity. Based on the received information, the I-SMF uses N4 to establish between the source UL CL and target UL CL the N9 forwarding tunnel to support the EAS session continuity. The I-SMF configures the source UL CL to forward traffic received from source L-PSA related to that PDU session toward the target UL CL via the N9 forwarding tunnel. 9. Same as steps 6-8 of clause 4.3.5.4. The I-SMF updates (R)AN for uplink traffic. 10-11. If a N9 forwarding tunnel to support the EAS session continuity is not established between the source UL CL and target UL CL, the I-SMF releases via N4 the source UL-CL/BP as the source UL-CL/BP is replaced by the target UL-CL/BP. The I-SMF also releases via N4 the PSA0 if PSA0 is not collocated with source UL CL/BP ; 12. This step is the same as step 9 in clause 4.23.9.3. 12a. If a N9 forwarding tunnel to support the EAS session continuity is established between the source UL CL and target UL CL, the I-SMF releases the source UL-CL/BP and PSA0 and the N9 forwarding tunnel in target UL CL when detection of no active traffic over the N9 forwarding tunnel takes place per the value of the timer to detect the end of activity on the N9 forwarding tunnel to support the EAS session continuity received from SMF. The detection can be done by Source UL CL, which notifies the I-SMF of no active traffic over the N9 forwarding tunnel. The I-SMF invokes Nsmf_PDUSession_Update Request to inform the SMF of the release of the resource in UL CL/BP and PSA0 for the PDU Session.