3GPP 23.501 v20.2.0 — the document's own text
5.32.6.3.1 ATSSS-LL Functionality
Taught in 11. Using two accesses at once (The 5G system architecture, in depth).
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 or MPQUIC-E functionality is required in the UE for MA PDU Session of type Ethernet.
In addition:
- When the UE neither supports the MPTCP functionality, nor the MPQUIC-UDP functionality, nor the MPQUIC-IP functionality, the ATSSS-LL functionality is mandatory in the UE for an MA PDU Session of type IP.
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).