Section: 5.6.8 Selective activation and deactivation of UP connection of existing PDU Session
Content: This clause applies to the case when a UE has established multiple PDU Sessions. The activation of a UP connection of an existing PDU Session causes the activation of its UE-CN User Plane connection (i.e. data radio bearer and N3 tunnel). For the activation of a UP connection the service area restrictions as specified in clause 5.3.4.1.1 apply. For the UE in the CM-IDLE state in 3GPP access, either UE or Network-Triggered Service Request procedure may support independent activation of UP connection of existing PDU Session. For the UE in the CM-IDLE state in non-3GPP access, UE-Triggered Service Request procedure allows the re-activation of UP connection of existing PDU Sessions, and may support independent activation of UP connection of existing PDU Session. A UE in the CM-CONNECTED state invokes a Service Request (see clause 4.2.3.2 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3]) procedure to request the independent activation of the UP connection of existing PDU Sessions. Network Triggered re-activation of UP connection of existing PDU Sessions is handled as follows: - If the UE CM state in the AMF is already CM-CONNECTED on the access (3GPP, non-3GPP) associated to the PDU Session in the SMF, the network may re-activate the UP connection of a PDU Session using a Network Initiated Service Request procedure. Otherwise: - If the UE is registered in both 3GPP and non-3GPP accesses and the UE CM state in the AMF is CM-IDLE in non-3GPP access, the UE can be paged or notified through the 3GPP access for a PDU Session associated in the SMF (i.e. last routed) to the non-3GPP access: - If the UE CM state in the AMF is CM-IDLE in 3GPP access, the paging message may include the access type associated with the PDU Session in the SMF. The UE, upon reception of the paging message containing an access type, shall reply to the 5GC via the 3GPP access using the NAS Service Request message, which shall contain the list of PDU Sessions associated with the received access type and whose UP connections can be re-activated over 3GPP (i.e. the list does not contain the PDU Sessions whose UP connections cannot be re-activated on 3GPP based on UE policies and whether the S-NSSAIs of these PDU Sessions are within the Allowed NSSAI for 3GPP access). If the PDU Session for which the UE has been paged is in the list of the PDU Sessions provided in the NAS Service Request and the paging was triggered by pending DL data, the 5GC shall re-activate the PDU Session UP connection over 3GPP access. If the paging was triggered by pending DL signalling, the Service Request succeeds without re-activating the PDU session UP connection over the 3GPP access and the pending DL signalling is delivered to the UE over the 3GPP access; - If the UE CM state in the AMF is CM-CONNECTED in 3GPP access, the notification message shall include the non-3GPP Access Type. The UE, upon reception of the notification message, shall reply to the 5GC via the 3GPP access using the NAS Service Request message, which shall contain the List of Allowed PDU Sessions that can be re-activated over 3GPP or an empty List of Allowed PDU Sessions if no PDU Sessions are allowed to be re-activated over 3GPP access. NOTE: A UE that is in a coverage of a non-3GPP access and has PDU Session(s) that are associated in the UE (i.e. last routed) to non-3GPP access, is assumed to attempt to connect to it without the need to be paged. - If the UE is registered in both 3GPP and non-3GPP accesses served by the same AMF and the UE CM state in the AMF is CM-IDLE in 3GPP access and is in CM-CONNECTED in non 3GPP access, the UE can be notified through the non-3GPP for a PDU Session associated in the SMF (i.e. last routed) to the 3GPP access. The notification message shall include the 3GPP Access Type. Upon reception of the notification message, when 3GPP access is available, the UE shall reply to the 5GC via the 3GPP access using the NAS Service Request message. In addition to the above, a PDU Session may be established as an always-on PDU Session as described in clause 5.6.13. The deactivation of the UP connection of an existing PDU Session causes the corresponding data radio bearer and N3 tunnel to be deactivated. The UP connection of different PDU Sessions can be deactivated independently when a UE is in CM-CONNECTED state in 3GPP access or non-3GPP access. At the deactivation of the UP of a PDU Session using a N9 tunnel whose end-point is controlled by an I-SMF, the N9 tunnel is preserved. If a PDU Session is an always-on PDU Session, the SMF should not deactivate a UP connection of this PDU Session due to inactivity.