5 ATSSS control procedures

24.1933GPPAccess Traffic Steering, Switching and SplittingStage 3TS

5.1 Introduction

The ATSSS control procedures include:

a) handling of multi-access PDU connectivity service procedures (see clause 5.2); and

b) access performance measurement procedures (see clause 5.3).

In clause 5.2, handling of multi-access PDU connectivity service procedures include following management procedures:

a) activation of multi-access PDU connectivity service;

b) re-activation of user-plane resources;

c) release of user-plane resources;

d) updating ATSSS parameters;

e) converting PDU session transferred from EPS to MA PDU session; and

f) PDU session establishment with network modification to MA PDU session.

In clause 5.3, access performance measurement procedures are performed by exchanges of PMF protocol messages between the PMF in a UE and the PMF in the UPF over the user plane. For MA PDU Sessions of IPv4, IPv6, or IPv4v6 PDU session type, the PMF protocol messages are transported using UDP. For MA PDU sessions of Ethernet PDU session type, the PMF protocol messages are transported using Ethernet frames. The protocol stacks of the PMF protocol are specified in clause 5.32.5.4 of 3GPP TS 23.501 [2].

5.2 Multi-access PDU connectivity service

Editor’s note: This clause will specify handling of multi-access PDU connectivity service. What content under this clause will be moved into TS 24.501 is FFS.

5.2.1 Activation of multi-access PDU connectivity service

Activating multi-access PDU connectivity service refers to the establishment of user-plane resources on both 3GPP access and non-3GPP access:

a) if the UE is registered over both 3GPP access and non-3GPP access in the same PLMN, the UE shall initiate the UE-requested PDU session establishment procedure as specified in clause 6.4.1.2 of 3GPP TS 24.501 [6] over 3GPP access or non-3GPP access. Over which access to initiate this UE-requested PDU session establishment procedure is UE implementation specific. When the UE receives the PDU SESSION ESTABLISHMENT ACCEPT message including the ATSSS container IE as specified in clause 6.4.1.3 of 3GPP TS 24.501 [6] and user plane resources are established in both accesses (e.g. received lower layer indication in 3GPP access and established IKEv2 tunnel in untrusted non-3GPP access), the UE shall consider that the MA PDU session has been established over both 3GPP access and non-3GPP access;

b) if the UE is registered over both 3GPP access and non-3GPP access in different PLMNs, the UE shall initiate the UE-requested PDU session establishment procedure as specified in clause 6.4.1.2 of 3GPP TS 24.501 [6] over 3GPP access and non-3GPP access sequentially. Over which access to first initiate the UE-requested PDU session establishment procedure is UE implementation specific. When the UE receives the PDU SESSION ESTABLISHMENT ACCEPT message including the ATSSS container IE as specified in clause 6.4.1.3 of 3GPP TS 24.501 [6] over the selected access, the UE shall consider that the MA PDU session has been established and the user plane resources of the MA PDU session on this access are successfully established. The UE shall then initiate the UE-requested PDU session establishment procedure with the same PDU Session ID, as specified in clause 6.4.1.2 of 3GPP TS 24.501 [6] over the other access, in order to establish user plane resources on the other access for the MA PDU session. If the UE receives the PDU SESSION ESTABLISHMENT ACCEPT message including the ATSSS container IE as specified in clause 6.4.1.3 of 3GPP TS 24.501 [6] over the other access, the UE shall consider that the user plane resources of the MA PDU session have been established over both 3GPP access and non-3GPP access; or

c) if the UE is registered to a PLMN over only one access, either 3GPP access or non-3GPP access, the UE shall initiate the UE-requested PDU session establishment procedure as specified in clause 6.4.1.2 of 3GPP TS 24.501 [6] over this access. When the UE receives the PDU SESSION ESTABLISHMENT ACCEPT message including the ATSSS container IE as specified in clause 6.4.1.3 of 3GPP TS 24.501 [6] over the access, the UE shall consider that the MA PDU session has been established and the user plane resources of the MA PDU session on this access are successfully established. When the UE at a later point in time registers over the other access, either in the same PLMN or in a different PLMN, the UE shall initiate the UE-requested PDU session establishment procedure with the same PDU Session ID as specified in clause 6.4.1.2 of 3GPP TS 24.501 [6] over the other access in order to establish user plane resources on the other access for the MA PDU session. If the UE receives the PDU SESSION ESTABLISHMENT ACCEPT message including the ATSSS container IE as specified in clause 6.4.1.3 of 3GPP TS 24.501 [6] over the other access, the UE shall consider that the user plane resources of the MA PDU session have been established over both 3GPP access and non-3GPP access.

5.2.2 Re-activation of user-plane resources

In order to re-establish the user-plane resources of an MA PDU session:

a) if the UE requests re-establishment of the user-plane resources of the MA PDU session over 3GPP access which were released, the UE shall include the Uplink data status IE indicating the related MA PDU session,

1) in the REGISTRATION REQUEST message when the registration procedure for mobility and periodic registration update is initiated by the UE over 3GPP access as specified in clause 5.5.1.3.2 of 3GPP TS 24.501 [6]; or

2) in the SERVICE REQUEST message when the service request procedure initiated by the UE over 3GPP access as specified in clause 5.6.1.2 of 3GPP TS 24.501 [6];

b) if the UE requests re-establishment of the user-plane resources of the MA PDU session over non-3GPP access which were released and the UE is in 5GMM-CONNECTED mode over non-3GPP access, the UE shall include the Uplink data status IE indicating the related MA PDU session,

1) in the REGISTRATION REQUEST message when the registration procedure for mobility registration update is initiated by the UE over non-3GPP access as specified in clause 5.5.1.3.2 of 3GPP TS 24.501 [6]; or

2) in the SERVICE REQUEST message when the service request procedure initiated by the UE over non-3GPP access as specified in clause 5.6.1.2 of 3GPP TS 24.501 [6];

c) if the UE requests re-establishment of the user-plane resources of the MA PDU session over non-3GPP access which were released and the UE is in 5GMM-IDLE mode over non-3GPP access,

1) for untrusted non-3GPP access, the UE shall perform the procedure as specified in clause 7.3 of 3GPP TS 24.502 [7] and include the Uplink data status IE indicating the related MA PDU session in the SERVICE REQUEST message when the service request procedure initiated by the UE over non-3GPP access as specified in clause 5.6.1.2 of 3GPP TS 24.501 [6]; or

2) for trusted non-3GPP access, the UE shall perform the procedures as specified in clause 7.3A of 3GPP TS 24.502 [7] and include the Uplink data status IE indicating the related MA PDU session in the SERVICE REQUEST message when the service request procedure initiated by the UE over non-3GPP access as specified in clause 5.6.1.2 of 3GPP TS 24.501 [6]; and

d) if the network requests re-establishment of the user-plane resources of the MA PDU session over 3GPP access which were released, the UE in 5GMM-IDLE mode over 3GPP access shall initiate the service request procedure by sending a SERVICE REQUEST message to the AMF upon receipt of the paging request as specified in clause 5.6.1.2 of 3GPP TS 24.501 [6].

NOTE: When the UE is in 5GMM-IDLE mode over non-3GPP access, the network does not request the UE to re-establish the user-plane resources of the MA PDU session over non-3GPP access which were released as specified in 3GPP TS 23.502 [3].

5.2.3 Release of user-plane resources

In order to release the MA PDU session’s user-plane resources of 3GPP access, of non-3GPP access or of both accesses:

a) the SMF shall initiate the network-requested PDU session release procedure as specified in clause 6.3.3.2 of 3GPP TS 24.501 [6] over 3GPP access or non-3GPP access, by sending the PDU SESSION RELEASE COMMAND message to the UE, e.g. when the AMF indicates to the SMF that the UE is deregistered over an access or when S-NSSAI of the MA PDU session is not in the Allowed NSSAI over an access. Over which access to initiate this network-requested PDU session release procedure is SMF implementation specific. To release the MA PDU session, the PDU SESSION RELEASE COMMAND message as specified in clause 6.4.3.2 of 3GPP TS 24.501 [6] shall include the Access type IE indicating of which access or of both accesses, the user-plane resources are released;

b) the UE shall initiate the UE-requested PDU session release procedure as specified in clause 6.4.3.2 of 3GPP TS 24.501 [6] over 3GPP access or non-3GPP access by sending the PDU SESSION RELEASE REQUEST message to the network. Over which access to initiate this UE-requested PDU session release procedure is UE implementation specific; and

c) when the UE receives the PDU SESSION RELEASE COMMAND message, the UE shall behave as specified in 3GPP TS 24.501 [6] clause 6.3.3.3, and consider that the user plane resources of the MA PDU session have been released over the accesses indicated in Access type IE.

5.2.4 Updating ATSSS parameters

An SMF can update ATSSS parameters, e.g. the ATSSS rules, according to the procedure for the network-requested PDU session modification as specified in clause 6.3.2 of 3GPP TS 24.501 [6] over 3GPP access network or non-3GPP access network. The SMF may change the access network over which the traffic of the GBR QoS flow is transmitted by updating the UE’s ATSSS rules.

Editor’s note: Whether the UE can request to update ATSSS rules is FFS.

5.2.5 Converting PDU session transferred from EPS to MA PDU session

When an ATSSS capable UE has transferred a PDN connection from S1 mode to N1 mode in the network supporting N26 interface and the related URSP or UE local configuration does not mandate the PDU session shall be established over a single access:

a) if the UE is registered over both 3GPP access and non-3GPP access in the same PLMN, the UE may initiate the UE-requested PDU session modification procedure by sending the PDU SESSION MODIFICATION REQUEST message including 5GSM capability IE over 3GPP access as specified in clause 6.4.2.2 of 3GPP TS 24.501 [6]. The UE may set the Request type IE to either:

1) "modification request" and include the MA PDU session information IE set to "MA PDU session network upgrade allowed" as specified in clause 9.11.3.63 of 3GPP TS 24.501 [6]; or

2) "MA PDU request"

in the UL NAS TRANSPORT message as specified in clause 8.2.10 of 3GPP TS 24.501 [6]. When the UE receives the PDU SESSION MODIFICATION COMMAND message including the ATSSS container IE as specified in clause 6.4.2.3 of 3GPP TS 24.501 [6], the UE shall consider that the requested PDU session was converted by the network to an MA PDU session and user plane resources are established in both 3GPP access and non-3GPP access;

b) if the UE is registered over both 3GPP access and non-3GPP access in a different PLMN, the UE may initiate the UE-requested PDU session modification procedure by sending the PDU SESSION MODIFICATION REQUEST message including 5GSM capability IE over 3GPP access as specified in clause 6.4.2.2 of 3GPP TS 24.501 [6]. The UE may set the Request type IE to either:

1) "modification request" and include the MA PDU session information IE set to "MA PDU session network upgrade allowed" as specified in clause 9.11.3.63 of 3GPP TS 24.501 [6]; or

2) "MA PDU request"

in the UL NAS TRANSPORT message as specified in clause 8.2.10 of 3GPP TS 24.501 [6]. When the UE receives the PDU SESSION MODIFICATION COMMAND message including the ATSSS container IE as specified in clause 6.4.2.3 of 3GPP TS 24.501 [6], the UE shall consider that the requested PDU session was converted by the network to an MA PDU session. The UE shall then initiate the UE-requested PDU session establishment procedure with the same PDU Session ID, as specified in clause 6.4.1.2 of 3GPP TS 24.501 [6] over non-3GPP access, in order to establish user plane resources on the other access for the MA PDU session; or

c) if the UE is registered over 3GPP access only, the UE may initiate the UE-requested PDU session modification procedure by sending the PDU SESSION MODIFICATION REQUEST message including 5GSM capability IE over 3GPP access as specified in clause 6.4.2.2 of 3GPP TS 24.501 [6], The UE may set the Request type IE to either:

1) "modification request" and include the MA PDU session information IE set to "MA PDU session network upgrade allowed" as specified in clause 9.11.3.63 of 3GPP TS 24.501 [6]; or

2) "MA PDU request"

in the UL NAS TRANSPORT message as specified in clause 8.2.10 of 3GPP TS 24.501 [6]. When the UE receives the PDU SESSION MODIFICATION COMMAND message including the ATSSS container IE as specified in clause 6.4.2.3 of 3GPP TS 24.501 [6], the UE shall consider that the requested PDU session was converted by the network to an MA PDU session. When the UE at a later point in time registers over the non-3GPP access, either in the same PLMN or in a different PLMN, the UE shall initiate the UE-requested PDU session establishment procedure with the same PDU Session ID as specified in clause 6.4.1.2 of 3GPP TS 24.501 [6] over non-3GPP access in order to establish user plane resources on non-3GPP access for the MA PDU session.

5.2.6 PDU session establishment with network modification to MA PDU session

When an ATSSS capable UE establishes a new PDU session and the related URSP or UE local configuration does not mandate the PDU session shall be established over a single access:

a) if the UE is registered over both 3GPP access and non-3GPP access in the same PLMN and the UE initiates the UE-requested PDU session establishment procedure over 3GPP access or non-3GPP access, the UE may include the MA PDU session information IE in the UL NAS TRANSPORT message and set the IE to "MA PDU session network upgrade is allowed" as specified in clause 9.11.3.63 of 3GPP TS 24.501 [6]. When the UE receives the PDU SESSION ESTABLISHMENT ACCEPT message including the ATSSS container IE as specified in clause 6.4.1.3 of 3GPP TS 24.501 [6], the UE shall consider that the requested PDU session is established as an MA PDU session;

b) if the UE is registered over both 3GPP access and non-3GPP access in different PLMNs and the UE initiates the UE-requested PDU session establishment procedure over 3GPP access or non-3GPP access, the UE may include the MA PDU session information IE in the UL NAS TRANSPORT message and shall set the IE to "MA PDU session network upgrade is allowed" as specified in clause 9.11.3.63 of 3GPP TS 24.501 [6]. When the UE receives the PDU SESSION ESTABLISHMENT ACCEPT message including the ATSSS container IE as specified in clause 6.4.1.3 of 3GPP TS 24.501 [6] over the access, the UE shall consider that the requested PDU session is established as an MA PDU session on this access. The UE shall then initiate the UE-requested PDU session establishment procedure with the same PDU Session ID, as specified in clause 6.4.1.2 of 3GPP TS 24.501 [6] over the other access, in order to establish user plane resources on the other access for the MA PDU session. If the UE receives the PDU SESSION ESTABLISHMENT ACCEPT message including the ATSSS container IE as specified in clause 6.4.1.3 of 3GPP TS 24.501 [6] over the other access, the UE shall consider that the user plane resources of the MA PDU session have been established over both 3GPP access and non-3GPP access; or

c) if the UE is registered to a PLMN over only one access, either 3GPP access or non-3GPP access, and the UE requests to establish a PDU session over this access, the UE may include the MA PDU session information IE in the UL NAS TRANSPORT message and shall set the IE to "MA PDU session network upgrade is allowed" as specified in clause 9.11.3.63 of 3GPP TS 24.501 [6]. When the UE receives the PDU SESSION ESTABLISHMENT ACCEPT message including the ATSSS container IE as specified in clause 6.4.1.3 of 3GPP TS 24.501 [6] over the access, the UE shall consider that the requested PDU session is established as an MA PDU session on this access. When the UE at a later point in time registers over the other access, either in the same PLMN or in a different PLMN, the UE shall initiate the UE-requested PDU session establishment procedure with the same PDU Session ID as specified in clause 6.4.1.2 of 3GPP TS 24.501 [6] over the other access in order to establish user plane resources on the other access for the MA PDU session. If the UE receives the PDU SESSION ESTABLISHMENT ACCEPT message including the ATSSS container IE as specified in clause 6.4.1.3 of 3GPP TS 24.501 [6] over the other access, the UE shall consider that the user plane resources of the MA PDU session have been established over both 3GPP access and non-3GPP access.

5.3 Access performance measurement procedures

5.3.1 UE-initiated RTT measurement

Editor’s note: The procedure for UE-initiated RTT measurement is FFS.

5.3.2 Network-initiated RTT measurement

Editor’s note: The procedure for Network-initiated RTT measurement is FFS.

5.4 Reporting of access availability procedures

Editor’s note: This clause will specify the procedures of UE notifying the network when an access should be considered as available or unavailable.