Content for  TS 23.502  Word version:  18.1.1

When the UE is registered to the same VPLMN over 3GPP access and non-3GPP access, the MA-PDU Session is established as specified in Figure 4.3.2.2.2-1 ("UE-requested PDU Session Establishment for home-routed roaming scenarios") with the differences and clarifications:

• The PDU Session Establishment Request message may be sent over the 3GPP access or over the non-3GPP access.
• In step 1, the UE provides Request Type as "MA PDU Request" in UL NAS Transport message and its ATSSS Capabilities, as defined in clause 5.32.2 of TS 23.501 in PDU Session Establishment Request message. The UE indicates to AMF whether it supports non-3GPP access path switching.
• In step 2, if the AMF supports MA PDU sessions, then the AMF selects a V-SMF and an H-SMF, which supports MA PDU sessions. The V-SMF serves the UE over both accesses. If the AMF supports non-3GPP access path switching and the UE indicated in step 1 that the UE supports non-3GPP access path switching, the AMF selects a V-SMF and H-SMF supporting non-3GPP access path switching.
• In step 3, the AMF informs the SMF that the request is for a MA PDU Session by including an "MA PDU Request" indication and, in addition, the AMF indicates to V-SMF that the UE is registered over both accesses. If the AMF supports non-3GPP access path switching and the UE indicated in step 1 that the UE supports non-3GPP access path switching, the AMF indicates to the V-SMF that the UE supports non-3GPP access path switching.
• In step 5, two DL N9 tunnel CN info and two UL N3 tunnel CN info are allocated by the V-SMF or by the V-UPF.
• In step 6, the V-SMF informs the H-SMF that the request is for a MA PDU Session by including an "MA PDU Request" indication and indicates to H-SMF that the UE is registered over both accesses. If the AMF indicated in step 3 that the AMF supports non-3GPP access path switching, the V-SMF indicates to H-SMF that the UE supports non-3GPP access path switching.
• In step 7, the H-SMF retrieves, via Session Management subscription data, the information whether the MA-PDU session is allowed or not.
• In step 9, if dynamic PCC is to be used for the MA-PDU Session, the H-SMF sends an "MA-PDU Request" indication to H-PCF in the SM Policy Control Create message and the ATSSS Capabilities of the MA-PDU session. The H-SMF provides the currently used list of Access Type(s) and RAT Type(s) for the MA-PDU session to the H-PCF. The H-PCF decides whether the MA-PDU session is allowed or not based on operator policy and subscription data.
  The H-PCF provides the PCC rules containing MA-PDU session control information and the H-SMF derives the ATSSS rules for the UE and the N4 rules for the H-UPF.
• In step 12, two UL N9 tunnel CN info are allocated by the H-SMF or by the H-UPF. After this step, the two N9 tunnels between the H-UPF and V-UPF are established.
• In step 13, the H-SMF sends "MA PDU session Accepted" indication to V-SMF in the Nsmf_PDUSession_Create Response message. If the V-SMF indicated in step 6 that the UE supports non-3GPP access path switching, and the H-SMF supports non-3GPP access path switching, the H-SMF includes a non-3GPP access path switching support indication in the Nsmf_PDUSession_Create Response message.
• In step 14, the V-SMF sends the "MA-PDU session Accepted" indication in the Namf_Communication_N1N2MessageTransfer message to the AMF and indicates the AMF to send the N2 SM Information included in this message over the access that the UE sent the PDU Session Establishment Request. The AMF marks this PDU session as MA-PDU session based on the received "MA-PDU session Accepted" indication.
  If the AMF indicated in step 3 that non-3GPP access path switching is supported, and the V-SMF and H-SMF support both non-3GPP access path switching, the V-SMF includes a non-3GPP access path switching support indication in the PDU Session Establishment Accept message.
  If the V-SMF received two UL N9 tunnel CN info from the H-SMF, the V-SMF also initiates the establishment of user-plane resources over the other access. The V-SMF sends an N1N2 Message Transfer to AMF including N2 SM Information and the other access type to indicate to AMF that the N2 SM Information should be sent over the other access. The N1N2 Message Transfer does not include an N1 SM Container for the UE which was sent to UE over the access that the UE sent the PDU Session Establishment Request.
• In step 16, the UE receives a PDU Session Establishment Accept message, which indicates to UE that the requested MA-PDU session was successfully established. This message includes the ATSSS rules for the MA-PDU session, which were derived by H-SMF and may include Measurement Assistance Information.
• After step 20, if the V-SMF was informed in step 3 that the UE is registered over both accesses, then the V-SMF initiates the establishment of user-plane resources over the other access too. The V-SMF sends an N1N2 Message Transfer to the AMF including N2 SM Information and indicates to the AMF over which access the N2 SM Information should be sent. The N1N2 Message Transfer does not include an N1 SM Container for the UE because this was sent to the UE in step 14. After this step, two N9 tunnels between the H-UPF and the V-UPF as well as two N3 tunnels between the V-UPF and RAN/AN are established, or, if the H-UPF is connected to two different V-UPFs, the H-UPF has one N9 tunnel with each V-UPF.

When the UE is registered to different PLMNs over 3GPP access and non-3GPP access, the MA-PDU Session is established first over one access as specified in Figure 4.3.2.2.2-1 ("UE-requested PDU Session Establishment for home-routed roaming scenarios") and then over the other access with the following differences and clarifications:

• In step 1, the UE provides Request Type as "MA PDU Request" in UL NAS Transport message and its ATSSS Capabilities, as defined in clause 5.32.2 of TS 23.501. The UE indicates to AMF whether it supports non-3GPP access path switching.
• In step 2, if the AMF supports MA PDU sessions, then the AMF selects a V-SMF, which supports MA PDU sessions. If the AMF supports non-3GPP access path switching and the UE indicated in step 1 that the UE supports non-3GPP access path switching, the AMF may select a V-SMF and H-SMF supporting non-3GPP access path switching.
• In step 3, the AMF informs the V-SMF that the request is for a MA PDU Session (i.e. it includes an "MA PDU Request" indication). If the AMF supports non-3GPP access path switching and the UE indicated in step 1 that the UE supports non-3GPP access path switching, the AMF indicates to V-SMF that the UE supports non-3GPP access path switching.
• In step 6, the V-SMF informs the H-SMF that the request is for a MA PDU Session (i.e. it includes an "MA PDU Request" indication). If the AMF indicated in step 3 that the AMF supports non-3GPP access path switching, the V-SMF indicates to the H-SMF that the UE supports non-3GPP access path switching.
• In step 7, the H-SMF retrieves, via Session Management subscription data, the information whether the MA-PDU session is allowed or not.
• In step 9, if dynamic PCC is to be used for the MA-PDU Session, the H-SMF sends an "MA-PDU Request" indication to PCF in the SM Policy Control Create message and the ATSSS Capabilities of the MA-PDU session. The H-SMF provides the currently used Access Type(s) and RAT Type(s) for the MA-PDU session to the PCF. The PCF decides whether the MA-PDU session is allowed or not based on operator policy and subscription data.
• In step 13, if the V-SMF indicated in step 6 that non-3GPP access path switching is supported, and the H-SMF supports non-3GPP access path switching, the H-SMF includes a non-3GPP access path switching support indication in the Nsmf_PDUSession_Create Response message.
• In step 14, if the AMF indicated in step 3 that non-3GPP access path switching is supported, and the V-SMF and H-SMF support both non-3GPP access path switching, the V-SMF includes a non-3GPP access path switching support indication in the PDU Session Establishment Accept message.
• In step 16, the UE receives a PDU Session Establishment Accept message, which indicates to UE that the requested MA-PDU session was successfully established. This message includes the ATSSS rules for the MA-PDU session, which were derived by H-SMF and may include Measurement Assistance Information.
• After the MA-PDU Session is successfully established on the first access, the UE shall initiate again the MA-PDU Session establishment procedure in Figure 4.3.2.2.2-1 over the other access with the following differences and clarifications:
  • In step 1, the UE shall send another PDU Session Establishment Request over the other access containing the same PDU Session ID that was provided over the first access. The UE also provides Request Type as "MA PDU Request" in UL NAS Transport message. The UE indicates to the AMF whether it supports non-3GPP access path switching.
  • In step 2, if the AMF supports non-3GPP access path switching and the UE indicated in step 1 that the UE supports non-3GPP access path switching, the AMF may select a V-SMF and H-SMF that support both non-3GPP access path switching.
  • In step 3, if the AMF supports non-3GPP access path switching and the UE indicated in step 1 that the UE supports non-3GPP access path switching, the AMF indicates to the V-SMF that the UE supports non-3GPP access path switching.
  • In step 12, new UL N9 tunnel CN info is allocated by the H-SMF or by the H-UPF.
  • In step 13, if the V-SMF indicated in step 6 that non-3GPP access path switching is supported, and the H-SMF supports non-3GPP access path switching, the H-SMF includes a non-3GPP access path switching support indication in the Nsmf_PDUSession_Create Response message.
  • In step 14, if the AMF indicated in step 3 that non-3GPP access path switching is supported, and the V-SMF and H-SMF support both non-3GPP access path switching, the V-SMF includes a non-3GPP access path switching support indication in the PDU Session Establishment Accept message.
  • In step 16, the UE receives another PDU Session Establishment Accept message, which may contain updated ATSSS rules for the MA-PDU session.
  • After step 20, two N9 tunnels between the H-UPF and two different V-UPFs as well as two N3 tunnels between different V-UPF and RAN/AN are established, or two N3 tunnels, one is between V-UPF and RAN/AN over 3GPP access and the other is between H-UPF and RAN/AN over non 3GPP access, as well as one N9 tunnel between H-UPF and V-UPF are established.

This clause applies to the case where, for a PDU Session, multi-access connectivity via both EPC (over 3GPP access) and 5GC (over non-3GPP access) is supported and allowed in the UE and network. In this case, multi-access connectivity using ATSSS via both 3GPP access to EPC and non-3GPP access to 5GC may be provided as described in this clause. For this scenario, the general principles for ATSSS as described in clause 5.32 of TS 23.501 apply, with the additions provided in this clause 4.22.2.3. A Multi-Access PDU Session may be extended with user-plane resources via an associated PDN Connection on 3GPP access in EPC. This enables a scenario where a MA-PDU Session can simultaneously be associated with user-plane resources on 3GPP access network connected to EPC and non-3GPP access connected to 5GC. Such a PDN Connection in EPS would thus be associated with multi-access capability in the UE and PGW-C+SMF. The UE may operate in either single-registration mode or dual-registration mode in 3GPP access. Irrespective of whether the UE operates in single-registration mode or dual-registration mode in 3GPP access, it is assumed that the UE supports simultaneous registrations for non-3GPP access in 5GC and 3GPP access in EPC. The ATSSS rules are provided from the PGW-C+SMF to the UE via SM NAS signalling over 5GC, as described in clause 5.32.2 of TS 23.501. ATSSS rules are not provided via the EPC. When a UE establishes a MA-PDU Session in 5GS, the UE indicates whether it supports 3GPP access leg over EPC. Based on the UE capability, the SMF determines whether the non-3GPP access should be released or not when the MA-PDU Session is moved to EPS as described in clause 4.22.6.2. After the establishment of a MA-PDU Session and setting up user-plane resources in 3GPP access in EPC and non-3GPP access in 5GC, the UE distributes the uplink traffic across the two access networks as described in clause 5.32.1 of TS 23.501. Similarly, the PDU Session Anchor UPF performs distribution of downlink traffic across the two access networks as described in clause 5.32.1 of TS 23.501. The PMF protocol may be used via any user plane connection, i.e. via 3GPP access in EPC or non-3GPP access in 5GC. The PCF functionality to support ATSSS, as described in clause 5.32.1 of TS 23.501 and TS 23.503 applies also in the case of interworking with EPC. When the 3GPP access leg of a MA-PDU Session using both 3GPP and non-3GPP access connected to 5GC is transferred to EPC, the PDU Session continues to work as a MA-PDU Session using E-UTRAN/EPC and non-3GPP access connected to 5GC, as described in clause 4.22.6.

When the UE wants to request a new PDN Connection in EPC and wants to use this PDN Connection as user-plane resource associated with a MA-PDU Session:

• The UE requests establishment of a new PDN Connection when the UE is registered via 3GPP access in EPS using PDN Connection Establishment procedure. The UE provides via PCO to PGW-C+SMF the following information:
  • An indication that the PDN Connection is requested to be associated with a MA-PDU Session
  • The UE's ATSSS capabilities as described in clause 5.32.2 of TS 23.501 (i.e. whether the UE is capable of supporting the ATSSS-LL functionality, the MPTCP functionality, the MPQUIC functionality, or any combination of them).
• The MME may select a PGW-C+SMF as described in TS 23.401 and clause 4.11.0a.4.
• The PGW-C+SMF determines based its capabilities whether the request can be accepted. The PCF decides whether the multi-access connectivity is allowed or not based on operator policy and subscription data, as described in clause 4.22.2. The PGW-C+SMF provides the following information in the PCO to the UE:
  • An indication whether the request for using the PDN Connection for MA-PDU Session is accepted or not.
  • If the UE has indicated that it is capable of supporting the MPTCP functionality and/or the MPQUIC functionality and the PGW-C+SMF accepts to activate the MPTCP functionality and/or the MPQUIC functionality, then the network provides MPTCP proxy information and/or MPQUIC proxy information to the UE, as described in clause 5.32.2 of TS 23.501.
  • UE Measurement Assistance Information (as described in clause 5.32.2 of TS 23.501).

After the PDN Connection establishment:

• If the UE registers to 5GC and wants to add non-3GPP user-plane resources, then the UE shall send a PDU Session Establishment Request over this access containing a "MA PDU Request" indication as described in clause 5.32.2 of TS 23.501.

When the UE wants to request a new MA-PDU Session in 5GC/non-3GPP access, the description in clause 5.32.2 of TS 23.501, applies. After the MA-PDU Session establishment in 5GS/non-3GPP access, the description in clause 5.32.2 of TS 23.501, applies with the following additions:

• If the UE is registered to EPC and wants to add user-plane resources on 3GPP access over EPC, then the UE shall send a PDN Connection Establishment Request over this access containing a "handover" indication and include a "MA-PDU Request" indication in the PCO as well as the PDU Session ID of the existing MA-PDU Session on non-3GPP access over 5GC.
• When the UE deregisters from the EPC access (but remains registered on the 5GC access), the MME will notify the PGW-C+SMF that the PDN Connection is released, as described in TS 23.401. The SMF can then notify the UPF that the access type has become unavailable.

In order to support EPS interworking when Ethernet type PDN Connection is not supported in EPS, the UE may use non-IP type PDN Connection when the UE establishes a PDN Connection in EPS as an added 3GPP access leg of an Ethernet type MA-PDU Session. In this case, the UE and SMF shall locally associate the PDN Connection as an Ethernet type PDU Session as described in TS 23.501. When Ethernet type PDN Connection is not supported in EPS, the UE does not request to establish a PDN Connection with "MA-PDU Request" indication before the UE registers to 5GS and establishes MA-PDU Session over non-3GPP access. A UE that has an established MA-PDU session over non-3GPP access in 5GC and 3GPP access in EPS, may be able to use EN-DC for the 3GPP access leg. Depending on the RAT types supported by the UE, the PDN connection may also be handed over to 3GPP access in 5GC. For a UE supporting both E-UTRAN/EPC access and NG-RAN/5GC access, the user plane resources for 3GPP access may be moved between E-UTRAN/EPC access and NG-RAN/5GC access as described in clause 5.17.2 of TS 23.501. The PDU Session and User Plane resources active over non-3GPP access are not affected by such inter 3GPP access RAT change.

The general principles for QoS support with ATSSS as described in clause 5.32.4 of TS 23.501, apply, with the clarifications provided in this clause. With an MA-PDU Session associated to a PDN Connection on EPS there may be separate user-plane tunnels between the AN and the PGW-U+UPF, one associated with 3GPP access in EPC and one associated with non-3GPP access in 5GS. As described in clause 4.11.1.1, the PGW-C+SMF maps the 5G QoS information received from PCC to EPS QoS parameters. This mapping is e.g. based on operator configuration and may result in that multiple QoS flows are mapped to a single EPS bearer. The PGW-C+SMF applies the appropriate QoS signalling in each access, e.g. to manage dedicated bearers in the access associated with EPC and QoS flows in the access associated with 5GC. The PGW-C+SMF also provides N4 rules to UPF for performing QoS enforcement and for mapping downlink traffic to appropriate GTP-U tunnels. As described in clause 5.32.4 of TS 23.501, for a GBR QoS flow, the QoS profile is provided to a single access network at a given time. GBR QoS flows (and associated MBR, GBR) are thus only enforced in either the access associated to EPC or the access associated to 5GC. In order to maintain consistency between QoS information received via AS and NAS layers in each system, the PGW-C+SMF only provides the GBR QoS information to the UE for the access where the GBR traffic is enforced. The UE shall treat the uplink traffic sent via EPC according to the EPS QoS information received in EPC (e.g. UL TFTs) and the uplink traffic sent via 5GC according to the 5G QoS rules received in 5GS. The UE thus need to determine what access to use (3GPP and Non-3GPP) before applying the uplink QoS treatment. The UPF shall treat the downlink traffic according to the N4 rules (QER, etc.) received from PGW-C+SMF.

This clause applies to the case where, for a PDU Session, multi-access connectivity via both EPC (over 3GPP access) and 5GC (over non-3GPP access) is supported and allowed in the UE and network. In this case, multi-access connectivity using ATSSS via both non-3GPP access to EPC and 3GPP access to 5GC may be provided as described in this clause. For this scenario, the general principles for ATSSS as described in clause 5.32 of TS 23.501 apply, with the additions provided in this clause 4.22.2.3. A Multi-Access PDU Session may be extended with user-plane resources via an associated PDN Connection on non-3GPP access in EPC. This enables a scenario where a MA PDU Session can simultaneously be associated with user-plane resources on non-3GPP access network connected to EPC and 3GPP access connected to 5GC. Such a PDN Connection in EPS would thus be associated with multi-access capability in the UE and PGW-C+SMF. The UE may operate in either single-registration mode or dual-registration mode in 3GPP access. Irrespective of whether the UE operates in single-registration mode or dual-registration mode in 3GPP access, it is assumed that the UE supports simultaneous registrations for 3GPP access in 5GC and non-3GPP access in EPC. The ATSSS rules are provided from the PGW-C+SMF to the UE via SM NAS signalling over 5GC, as described in clause 5.32.2 of TS 23.501. ATSSS rules may be provided via the EPC. When a UE establishes a MA PDU Session in 5GS, the UE indicates whether it supports non-3GPP access leg over EPC. Based on the UE capability, the SMF determines whether the 3GPP access should be released or not when the MA PDU Session is moved to EPS as described in clause 4.22.6.2. After the establishment of a MA PDU Session and setting up user-plane resources in non-3GPP access in EPC and 3GPP access in 5GC, the UE distributes the uplink traffic across the two access networks as described in clause 5.32.1 of TS 23.501. Similarly, the PDU Session Anchor UPF performs distribution of downlink traffic across the two access networks as described in clause 5.32.1 of TS 23.501. The PMF protocol may be used via any user plane connection, i.e. via non-3GPP access in EPC or 3GPP access in 5GC. The PCF functionality to support ATSSS, as described in clause 5.32.1 of TS 23.501 and TS 23.503 applies also in the case of interworking with EPC. When the 3GPP access leg of a MA PDU Session using one 3GPP access path via 5GC and one non-3GPP access path via ePDG is transferred to EPC, the PDU Session may continue to work as a MA PDU Session using E-UTRAN/EPC and non-3GPP access connected to ePDG, as described in clause 4.22.6.

When the UE wants to request a new PDN Connection in EPC and wants to use this PDN Connection as user-plane resource associated with a MA PDU Session:

• The UE requests establishment of a new PDN Connection when the UE is registered via non-3GPP access in EPS using PDN Connection Establishment procedure. The UE provides the following ATSSS information to ePDG via IKE signalling:
  • An indication that the PDN Connection is requested to be associated with a MA PDU Session
  • The UE's ATSSS capabilities as described in clause 5.32.2 of TS 23.501 (i.e. whether the UE is capable of supporting any combination of the ATSSS-LL functionality, the MPTCP functionality, and the MPQUIC functionality).
• The ePDG may select a PGW-C+SMF as described in TS 23.402. The ePDG forwards the ATSSS information to the selected PGW-C+SMF via APCO in Create Session Request message.
• The PGW-C+SMF determines based its capabilities whether the request can be accepted. The PCF decides whether the multi-access connectivity is allowed or not based on operator policy and subscription data, as described in clause 4.22.2. The PGW-C+SMF provides the following information via the APCO in the Create Session Response message to the ePDG:
  • An indication whether the request for using the PDN Connection for MA-PDU Session is accepted or not.
  • If the UE has indicated that it is capable of supporting the MPTCP functionality and the PGW-C+SMF accepts to activate the MPTCP functionality, then the network provides MPTCP proxy information to the UE, as described in clause 5.32.2 of TS 23.501.
  • If the UE has indicated that it is capable of supporting the MPQUIC functionality and the PGW-C+SMF accepts to activate the MPQUIC functionality, then the network provides MPQUIC proxy information to the UE, as described in clause 5.32.2 of TS 23.501.
  • UE Measurement Assistance Information (as described in clause 5.32.2 of TS 23.501).
  • ATSSS rules
• The ePDG forwards the received above information to the UE via IKE signalling.

After the PDN Connection establishment:

• If the UE registers to 5GC and wants to add 3GPP user-plane resources, then the UE shall send a PDU Session Establishment Request over this access containing a "MA PDU Request" indication as described in clause 5.32.2 of TS 23.501.

When the UE wants to request a new MA PDU Session in 5GC/3GPP access, the description in clause 5.32.2 of TS 23.501, applies. After the MA PDU Session establishment in 5GS/3GPP access, the description in clause 5.32.2 of TS 23.501, applies with the following additions:

• If the UE is registered to EPC and wants to add user-plane resources on non-3GPP access over EPC, then the UE shall send a PDN Connection Establishment Request over this access containing the IP address of the MA PDU Session in CFG_REQUEST Configuration Payload, and include a "MA PDU Request" indication and UE's ATSSS capabilities and the PDU Session ID of the existing MA PDU Session on 3GPP access over 5GC. The ePDG forwards the ATSSS information via the APCO in the Create Session Request message to the PGW-C/SMF.
• When the UE deregisters from the EPC access (but remains registered on the 5GC access), the ePDG will notify the PGW-C+SMF that the PDN Connection is released, as described in TS 23.402. The SMF can then notify the UPF that the access type has become unavailable.

A UE that has an established MA-PDU session over 3GPP access in 5GC and non-3GPP access in EPS, may be able to use Dual Connectivity for the 3GPP access leg. Depending on the RAT types supported by the UE, the PDU Session may also be handed over to 3GPP access in EPC. For a UE supporting both E-UTRAN/EPC access and NG-RAN/5GC access, the user plane resources for 3GPP access may be moved between E-UTRAN/EPC access and NG-RAN/5GC access as described in clause 5.17.2 of TS 23.501. The SMF+PGW-C may keep the MA PDU Session when the user plane resources of the MA PDU Session is only established in EPS over both accesses.

Based on the signalling flow in Figure 4.11.1.2.1-1, the procedure is performed with the following differences and modifications:

• Step 2 is also performed with all the SMF+PGW-Cs corresponding to MA-PDU Sessions with allocated EBI(s).
• In step 12e, the AMF requests the release of the 3GPP access of the MA-PDU Session which has resources established for 3GPP access, but not expected to be transferred to EPC, i.e. no EBI(s) allocated to the MA-PDU Session by triggering Nsmf_PDUSession_UpdateSMContext service operation.
• In step 16, if the MA PDU Session is established in both 3GPP and non-3GPP accesses and the MA PDU Session is moved to EPS and if the UE or the network does not supports MA PDU Session with 3GPP access connected to EPC, the SMF triggers the MA PDU Session Release procedure over non-3GPP access. If UE and the network support MA PDU Session with 3GPP access connected to EPC, the SMF should keep the user-plane resources over non-3GPP access in 5GC and use the PDN Connection as the 3GPP access leg of the MA PDU Session. If the MA PDU Session is established using one 3GPP access path via 5GC and one non-3GPP access path via ePDG/EPC and the MA PDU Session is moved to EPS and if the UE and network supports MA PDU Session with non-3GPP access connected to EPC, the SMF may keep the MA PDU Session.

Based on the signalling flow in Figure 4.11.1.3.2-1, the procedure is performed with the following differences and modifications:

• Step 5a is also performed with all the SMF+PGW-Cs corresponding to the MA-PDU Sessions with allocated EBI(s).
• In step 12, if the MA PDU Session is established in both 3GPP and non-3GPP accesses and the MA PDU Session is moved to EPS and if the UE or the network does not support MA PDU Session with 3GPP access connected to EPC, the SMF triggers the MA PDU Session Release procedure over non-3GPP access. If UE and the network support MA PDU Session with 3GPP access connected to EPC, the SMF should keep the user-plane resources over non-3GPP access in 5GC and use the PDN Connection as the 3GPP access leg of the MA PDU Session. If the MA PDU Session is established using one 3GPP access path via 5GC and one non-3GPP access path via ePDG/EPC and the MA PDU Session is moved to EPS and if the UE and network supports MA PDU Session with non-3GPP access connected to EPC, the SMF may keep the MA PDU Session.
• In step 15a, the AMF also requests the release of the MA-PDU Session which has resources established for 3GPP access, but not expected to be transferred to EPS, i.e. no EBI(s) allocated to the MA-PDU Session by triggering Nsmf_PDUSession_UpdateSMContext service operation.

Based on the signalling flow in Figure 4.11.1.4.1-1, additionally for the MA-PDU Session, with the following differences and clarifications:

• In step 1, the following procedures and relevant steps are also initiated during the UE Requested MA-PDU Session Establishment, the UE Requested PDU Session Establishment with Network Modification to MA-PDU Session and the UE or network requested MA-PDU Session Modification procedures.
• In step 2, if the QoS Flow(s) of the MA-PDU Session is established and the MA-PDU Session is established over 3GPP access and other existing conditions satisfies EPS interworking, the SMF requests EBI allocation for the QoS Flow(s) of the MA-PDU Session.

Based on the clause 4.11.1.4.3, additionally the following procedures are updated to revoke the EPS bearer ID(s) assigned to the QoS Flow(s) in the MA-PDU Session:

• UE or network requested MA-PDU Session Release (non-roaming and roaming with local breakout) in clause 4.22.10.2.
• UE or network requested MA-PDU Session Release (home-routed roaming) in clause 4.22.10.3.
• UE or network requested MA-PDU Session Modification (non-roaming and roaming with local breakout) in clause 4.22.8.2.
• UE or network requested MA-PDU Session Modification (home-routed roaming) in clause 4.22.8.3.
• When the MA-PDU Session is released over 3GPP access, the UE and the SMF locally release the EBI(s) for the MA-PDU Session. The SMF notifies the AMF of the released EBI(s) by sending Nsmf_PDUSession_SMContextStatusNotify service operation if the MA-PDU Session is established in the same PLMN. If the MA-PDU Session is established in different PLMNs, the SMF notifies the release of the MA-PDU Session and as a result, the AMF removes associated EBI(s).

Based on the signalling flow in Figure 4.11.2.2-1, the procedure is performed with the following differences and modifications:

• In step 10 (and step 13 in clause 4.11.2.4.1), if the MA-PDU Session is established in both 3GPP and non-3GPP accesses and the MA-PDU Session is moved to EPS and if the UE and the network does not support MA-PDU Session with 3GPP access connected to EPC, the PGW-C + SMF triggers the MA-PDU Session Release procedure over non-3GPP access. PGW-C + SMF and UE locally release the context related to ATSSS operation, e.g. ATSSS rules and Measurement Assistance Information for the relevant session. If the UE and the network support MA-PDU Session with 3GPP access connected to EPC, the UE includes a "MA-PDU Request" indication and the PDU Session ID in the PCO, the SMF should keep the user-plane resources over non-3GPP access in 5GC and use the PDN Connection as the 3GPP access leg of the MA-PDU Session.
• In step 13, during the additional PDN Connectivity Procedure, if the MA-PDU Session is established in both 3GPP and non-3GPP accesses and if the UE and the network support MA-PDU Session with 3GPP access connected to EPC, the UE includes a "MA-PDU Request" indication and the PDU Session ID in the PCO, the SMF should keep the user-plane resources over non-3GPP access in 5GC and use the PDN Connection as the 3GPP access leg of the MA-PDU Session. If the UE and the network does not support MA-PDU Session with 3GPP access connected to EPC and the MA-PDU Session is moved to EPS, the PGW-C + SMF triggers the MA-PDU Session Release procedure over non-3GPP access. PGW-C + SMF and UE locally release the context related to ATSSS operation, e.g. ATSSS rules and Measurement Assistance Information for the relevant session(s).
• Step 14 is also performed for the MA-PDU session(s) transferred to EPS.