Section: 5.32.6.3.1 ATSSS-LL Functionality
Content: The ATSSS-LL functionality in the UE does not apply a specific protocol. It is a data switching function, which decides how to steer, switch and split the uplink traffic across 3GPP and non-3GPP accesses, based on the provisioned ATSSS rules and local conditions (e.g. signal loss conditions). The ATSSS-LL functionality in the UE may be applied to steer, switch and split all types of traffic, including TCP traffic, UDP traffic, Ethernet traffic, etc. The ATSSS-LL functionality does not support the Redundant Steering Mode. The ATSSS-LL functionality may be enabled in the UE when the UE provides an "ATSSS-LL capability" during the PDU Session Establishment procedure. The ATSSS-LL functionality is mandatory in the UE for MA PDU Session of type Ethernet. In addition: - When the UE neither supports the MPTCP functionality nor the MPQUIC functionality, the ATSSS-LL functionality is mandatory in the UE for an MA PDU Session of type IP. - When the UE supports the MPTCP functionality and does not support the MPQUIC functionality, the ATSSS-LL functionality with Active-Standby Steering Mode is mandatory in the UE for an MA PDU Session of type IP to support non-MPTCP traffic. - When the UE supports the MPQUIC functionality and does not support the MPTCP functionality, the ATSSS-LL functionality with Active-Standby Steering Mode is mandatory in the UE for an MA PDU Session of type IP to support non-MPQUIC traffic. - When the UE supports both the MPTCP functionality and the MPQUIC functionality, the ATSSS-LL functionality with Active-Standby Steering Mode is mandatory in the UE for an MA PDU Session of type IP to support non-MPTCP and non-MPQUIC traffic. The network shall also support the ATSSS-LL functionality as defined for the UE. The ATSSS-LL functionality in the UPF is enabled for a MA PDU Session by ATSSS-LL functionality indication received in the Multi-Access Rules (MAR).