5.32.3 Policy for ATSSS Control

If dynamic PCC is to be used for the MA PDU Session, the PCF may take ATSSS policy decisions and create PCC rules that contain MA PDU Session Control information, (as specified in TS 23.503 [45]), which determines how the uplink and the downlink traffic of the MA PDU Session should be distributed across the 3GPP and non-3GPP accesses. If dynamic PCC is not deployed, local policy in SMF is used.

The SMF receives the PCC rules with MA PDU Session Control information and maps these rules into (a) ATSSS rules, which are sent to the UE and (b) N4 rules, which are sent to the UPF. The ATSSS rules are provided as a prioritized list of rules (see clause 5.32.8), which are applied by the UE to enforce the ATSSS policy in the uplink direction and the N4 Rules are applied by the UPF to enforce the ATSSS policy in the downlink direction.

The ATSSS rules are sent to UE with a NAS message when the MA PDU Session is created or updated by the SMF, e.g. after receiving updated/new PCC rules from the PCF. Similarly, the N4 rules are sent to UPF when the MA PDU Session is created or updated by the SMF.

The details of the policy control related to ATSSS are specified in TS 23.503 [45].