Section: 4.11.0a.5 PDN Connection Establishment
Content: During establishment of non-emergency PDN connection in the EPC, the UE and the SMF+PGW-C exchange information via PCO as described in clause 5.15.7 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. For UE with 5GC NAS capability disabled (i.e. N1 mode is disabled), the UE may also allocate a PDU Session ID and send it to the SMF+PGW-C via PCO. If the SMF+PGW-C supports more than one S-NSSAI and the APN is valid for more than one S-NSSAI, before the SMF+PGW-C provides an S-NSSAI to the UE, the SMF+PGW-C should check such that the selected S-NSSAI is among the UE's subscribed S-NSSAIs which supports interworking with EPC and that the S-NSSAI is not subject to Network Slice-Specific Authentication and Authorization, by retrieving the Subscribed S-NSSAI from UDM using the Nudm_SDM_Get service operation (the SMF+PGW-C discovers and selects a UDM as described in clause 6.3.8 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]). If the SMF+PGW-C is in a VPLMN, the SMF+PGW-C uses the Nnssf_NSSelection_Get service operation to retrieve a mapping of the Subscribed S-NSSAIs to Serving PLMN S-NSSAI values. If the S-NSSAIs supported by the SMF+PGW-C are all subject to NSSAA, then the SMF+PGW-C should reject the PDN connection establishment. If the selected S-NSSAI is subject to NSAC and EPS counting is required for the S-NSSAI, the SMF+PGW-C uses the Nnsacf_NSAC_NumberOfUEsUpdate services operation and/or the Nnsacf_NSAC_NumberOfPDUsUpdate services operation to check if the selected S-NSSAI is available as described in clause 4.11.5.9. The SMF+PGW-C uses the Nudm_SDM_Subscribe service operation to subscribe the change of the Session Management Subscription data. If the SMF+PGW-C is notified from UDM with subscription data change, the SMF+ PGW-C takes actions for the PDN connection as described in clause 5.17.2.1 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. As described in TS 23.548[ 5G System Enhancements for Edge Computing; Stage 2 ]  [74], during establishment of a PDN connection, a UE that hosts EEC(s) may indicate to the SMF+PGW-C, in the PCO, that it supports the ability to receive ECS address(es) via NAS and to transfer the ECS Address(es) to the EEC(s). If the UE indicated in the PCO that it supports the ability to receive ECS address(es) via NAS, the SMF+PGW-C may provide the ECS Address Configuration Information (as described in clause 6.5.2 of TS 23.548[ 5G System Enhancements for Edge Computing; Stage 2 ]  [74]) to the UE in the PCO. The SMF+PGW-C may derive the Edge Configuration Server Information based on local configuration, the UE's location and/or UE subscription information. The SMF+PGW-C may use the bearer modification procedure without bearer QoS update to send the UE a PCO with updated ECS Address Configuration Information as defined in clause 6.5.2 of TS 23.548[ 5G System Enhancements for Edge Computing; Stage 2 ]  [74] to the UE. During establishment of non-emergency PDN connection in the EPC, if PGW-C+SMF is selected for a UE that has 5GS subscription, the SMF may be configured to obtain the subscribed IP index from UDM as part of subscription data using the Nudm_SDM_Get service operation (the PGW-C+SMF discovers and selects a UDM as described in clause 6.3.8 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]). During establishment of non-emergency PDN connection in EPC, if PGW-C+SMF is selected for a UE that has 5GS subscription, the SMF may be configured to obtain the subscribed User Plane Security Policy from UDM as part of subscription data using the Nudm_SDM_Get service operation (the PGW-C+SMF discovers and selects a UDM as described in clause 6.3.8 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]). The SMF uses the subscribed User Plane Security Policy as described in clause 5.10.3 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. During establishment of non-emergency PDN connection in the EPC, if SMF+PGW-C is selected for a UE that has 5GS subscription but does not support 5GC NAS and is accessing via EPC/E-UTRAN and if the SMF+PGW-C supports more than one S-NSSAI and the APN is valid for more than one S-NSSAI, the SMF+PGW-C+PGW-C may proceed as specified in first paragraph of this clause or select any S-NSSAI associated with the APN of the PDN connection. The SMF+PGW-C shall not provide any 5GS related parameters to the UE. NOTE 1: The SMF+PGW-C knows that the UE does not support 5GS NAS if the UE does not provide PDU Session ID in PCO (see clause 5.15.7 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]). During establishment of emergency PDN connection: - The SMF+PGW-C is to be derived from the emergency APN or to be statically configured in the Emergency Configuration Data in MME. - 5GC interworking support with N26 or without N26 is determined based on UE's 5G NAS capability and local configuration (in the Emergency Configuration Data in MME). - The S-NSSAI configured for the emergency APN in SMF+PGW-C is not sent to the UE by the SMF+PGW-C. One S-NSSAI is configured for the emergency APN. During establishment of non-emergency PDN connection and emergency PDN connection, if SMF+PGW-C is selected for a UE that does not support 5GC NAS, the SMF+PGW-C creates unique PDU Session ID for each PDN connection of the UE. - The unique PDU Session ID can be created based on the EPS Bearer IDs assigned by the MME for the PDN Connections associated with the UE and not be in the range of PDU Session ID values that can be created by a 5GC NAS capable UE. - If handover between EPS and EPC/ePDG (as specified in clause 8.6 of TS 23.402[ Architecture enhancements for non-3GPP accesses ]  [26]) is required, the SMF+PGW-C, based on operator configuration, may perform the following to ensure the uniqueness of PDU Session ID: - the SMF+PGW-C queries the UDM for any PDU Session ID(s) that are already registered in the UDM for the UE by invoking Nudm_UECM_Get service operation. - the SMF+PGW-C creates a PDU session ID that does not collide with the received PDU session ID(s). - When the SMF+PGW-C establishes the PDN connection successfully, the SMF+PGW-C performs UDM registration using the Nudm_UECM_Registration service operation. NOTE 2: If the scenario that a UE handovers a PDN connection with APN1 established via MME to ePDG and then establishes a second PDN connection with APN2 via MME needs to be supported in a given deployment, then, based on operator configuration, the SMF+PGW-C can query the UDM to avoid that the same PDU Session ID value of first PDN connection would be assigned by the SMF+PGW-C for the second PDN connection. When the SMF+PGW-C establishes the PDN connection successfully, the SMF+PGW-C provides the ID of the PCF ID selected for the PDN connection in the UDM using the Nudm_UECM_Registration service operation. A SMF+PGW-C may support L2TP as described in clause 4.3.2.4. In this case step 1 and step 7 of Figure 4.3.2.4-1 correspond to a PDN Connection establishment and a SMF+PGW-C replaces the SMF in that Figure. To support User Plane Integrity Protection with EPS and policies that Require User Plane integrity protection to be used, at PDN connection establishment, the MME shall indicate to the SMF+PGW-C (via the Serving GW) whether the UE, the current eNB and the MME support User Plane Integrity Protection in EPS. If the MME and the UE support User Plane Integrity Protection, then the SMF+PGW-C informs the MME of the User Plane integrity protection policy (Required, Preferred, Not Needed) applicable to the PDN connection on a per-EPS bearer basis. In turn, the MME informs the eNB. To support URSP Provisioning in EPS, during Initial Attach with default PDN connection establishment procedure in EPS, the UE provides the "Indication of URSP Provisioning Support in EPS" in the PCO or in the ePCO in the PDN connectivity request as described in clause 5.17.8 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. If the SMF+PGW-C supports URSP Provisioning in EPS and the ePCO capability, it provides the "Indication of URSP Provisioning Support in EPS" in the ePCO in the Create Session Response. If the UE receives the "Indication of URSP Provisioning Support in EPS" in the ePCO from SMF+PGW-C provided in the PDN Connectivity Accept message, the UE initiates the UE requested bearer resource modification procedure and includes the UE Policy Container in the ePCO in the Request Bearer Resource Modification message, see clause 4.11.0a.10. If the default PDN connection is not established during Initial Attach procedure, the aforementioned procedure happens during the first request for PDN connectivity. If the negotiation of the support of URSP provisioning in EPS fails for the first PDN connection the UE may retry the aforementioned procedure successively for the next PDN connectivity requests until it succeeds for one of them as specified in clause 5.17.8 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]