Section: 5.6.5 Support for Local Area Data Network
Content: The access to a DN via a PDU Session for a LADN is only available in a specific LADN service area. A LADN service area is a set of Tracking Areas. LADN is a service provided by the serving PLMN or the serving SNPN. It includes: - LADN service applies only to 3GPP accesses and does not apply in Home Routed case. - The usage of LADN DNN requires an explicit subscription to this DNN or subscription to a wildcard DNN. - Whether a DNN corresponds to a LADN service is an attribute of a DNN and is per PLMN or per SNPN. The UE is configured to know whether a DNN is a LADN DNN on a per-PLMN or per SNPN basis, and an association between application and LADN DNN. The configured association is considered to be a UE local configuration defined in TS 23.503[ Policy and charging control framework for the 5G System (5GS); Stage 2 ]  [45]. Alternatively, the UE gets the information whether a DNN is a LADN DNN from LADN Information during (re-)registration procedure as described in this clause. NOTE 1: No other procedure for configuring the UE to know whether a DNN is a LADN DNN is defined in this release of the specifications. NOTE 2: The procedure for configuring the UE to know an association between application and LADN DNN is not defined in this release of the specifications. LADN service area and LADN DNN are configured in the AMF on a per DN basis, i.e. for different UEs accessing the same LADN, the configured LADN service area is the same regardless of other factors (e.g. UE's Registration Area or UE subscription). NOTE 3: If a LADN is not available in any TA of an AMF's service area, the AMF is not required to be configured with any LADN related information for that DNN. LADN Information (i.e. LADN Service Area Information and LADN DNN) is provided by AMF to the UE during the Registration procedure or UE Configuration Update procedure. For each LADN DNN configured in the AMF, the corresponding LADN Service Area Information includes a set of Tracking Areas that belong to the Registration Area that the AMF assigns to the UE (i.e. the intersection of the LADN service area and the assigned Registration Area). The AMF shall not create Registration Area based on the availability of LADNs. NOTE 4: It is thus possible that the LADN Service Area Information sent by the AMF to the UE contains only a sub-set of the full LADN service area as the LADN service area can contain TA(s) outside of the registration area of the UE or outside of the area served by the AMF. When the UE performs a successful (re-)registration procedure, the AMF may provide to the UE, based on local configuration (e.g. via OAM) about LADN, on UE location, and on UE subscription information received from the UDM about subscribed DNN(s), the LADN Information for the list of LADN available to the UE in that Registration Area in the Registration Accept message. The UE may provide either the LADN DNN(s) to retrieve the LADN Information for the indicated LADN DNN(s) or an indication of Requesting LADN Information to retrieve the LADN Information for all LADN(s) available in the current Registration Area. The list of LADN is determined as follows: - If neither LADN DNN nor an indication of requesting LADN Information is provided in the Registration Request message, the list of LADN is the LADN DNN(s) in subscribed DNN list except for wildcard DNN. - If the UE provides LADN DNN(s) in the Registration Request message, the list of LADN is LADN DNN(s) the UE requested if the UE subscribed DNN(s) includes the requested LADN DNN or if a wildcard DNN is included in the UE's subscription data. NOTE 5: It is assumed that an application can use only one LADN DNN at a time. - If the UE provides an indication of requesting LADN Information in the Registration Request message, the list of LADN is all the LADN DNN(s) configured in the AMF if the wildcard DNN is subscribed, or the LADN DNN(s) which is in subscribed DNN list and no wildcard DNN is subscribed. The UE considers the retrieved LADN Information valid only for the registered PLMN and the E-PLMN(s) if the LADN Service Area Information includes Tracking Areas that belong to E-PLMN(s). Additionally, an LADN DNN discovered by the UE via the retrieved LADN Information is considered an LADN DNN also in the E-PLMNs of the Registered PLMN, i.e. the UE can request LADN Information for the discovered LADN DNN in the E-PLMNs. During the subsequent Registration procedure, if the network does not provide LADN Information for a DNN, the UE deletes any LADN Information for that DNN. When the LADN Information for the UE in the 5GC is changed, the AMF shall update LADN Information to the UE through UE Configuration Update/Registration procedure as described in clauses 4.2.4 / 4.2.2.2.2 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3]. When receiving PDU Session Establishment with LADN DNN or Service Request for the established PDU Session corresponding to LADN, the AMF determines UE presence in LADN service area and forwards it to the SMF if the requested DNN is configured at the AMF as a LADN DNN. Based on the LADN Service Area Information in the UE, the UE determines whether it is in or out of a LADN service area. If the UE does not have the LADN Service Area Information for a LADN DNN, the UE shall consider it is out of the LADN service area. The UE takes actions as follows: a) When the UE is out of a LADN service area, the UE: - shall not request to activate UP connection of a PDU Session for this LADN DNN; - shall not attempt to send user data as payload of a NAS message (see clause 5.31.4.1) using a PDU Session for this LADN DNN; - shall not establish/modify a PDU Session for this LADN DNN (except for PS Data Off status change reporting for an established PDU Session); - need not release any existing PDU Session for this LADN DNN unless UE receives explicit SM PDU Session Release Request message from the network. b) When the UE is in a LADN service area, the UE: - may request a PDU Session Establishment/Modification for this LADN DNN; - may request to activate UP connection of the existing PDU Session for this LADN DNN; - may attempt to send user data as payload of a NAS message (see clause 5.31.4.1) using a PDU Session for this LADN DNN. NOTE 6: The evaluation of Service Area Restrictions will be performed before the evaluation of LADN service area, if the UE has overlapping areas between Service Area Restrictions and LADN service area. The SMF supporting a DNN is configured with information about whether this DNN is a LADN DNN or not. When receiving SM request corresponding an LADN from the AMF, the SMF determines whether the UE is inside LADN service area based on the indication (i.e. UE Presence in LADN service area) received from the AMF. If the SMF does not receive the indication, the SMF considers that the UE is outside of the LADN service area. The SMF shall reject the request if the UE is outside of the LADN service area. When the SMF receives a request for PDU Session Establishment with the LADN DNN, it shall subscribe to "UE mobility event notification" for reporting UE presence in Area of Interest by providing LADN DNN to the AMF as described in clauses 5.6.11 and 5.3.4.4. Based on the notification about the UE presence in LADN service area notified by AMF (i.e. IN, OUT, or UNKNOWN), the SMF takes actions as follows based on operator's policy: a) When SMF is informed that the UE presence in a LADN service area is OUT, the SMF shall: - release the PDU Session immediately; or - deactivate the user plane connection for the PDU Session and it shall not attempt to send user data as payload of a NAS message (see clause 5.31.4.1) while maintaining the PDU Session and ensure the Data Notification is disabled and the SMF may release the PDU Session if the SMF is not informed that the UE moves into the LADN service area after a period. b) When SMF is informed that the UE presence a LADN service area is IN, the SMF shall: - ensure that Data Notification is enabled. - trigger the Network triggered Service Request procedure for a LADN PDU Session to active the UP connection or send user data as payload of a NAS message (see clause 5.31.4.1) when the SMF receives downlink data or Data Notification from UPF. c) When the SMF is informed that the UE presence in a LADN service area is UNKNOWN, the SMF may: - ensure that Data Notification is enabled. - trigger the Network triggered Service Request procedure for a LADN PDU Session to active the UP connection or send user data as payload of a NAS message (see clause 5.31.4.1) when the SMF receives downlink data or Data Notification from UPF. SMF may make use of UE mobility analytics provided by NWDAF, as described in clause 6.7.2 of TS 23.288[ Architecture enhancements for 5G System (5GS) to support network data analytics services ]  [86], to determine UE presence pattern in LADN service area and take a decision how to handle LADN PDN Session (e.g. release the PDU Session immediately, or deactivate the user plane connection for the PDU Session with maintaining the PDU Session).