3GPP 23.501 v20.2.0 — the document's own text
5.32.5.6 Suspend and Resume Traffic Duplication
Taught in 11. Using two accesses at once (The 5G system architecture, in depth).
As part of the Redundant Steering Mode, a UPF can decide to suspend traffic duplication for a UE by sending PMF- Suspend Duplication Request message to the UE. How the UPF determines to suspend traffic duplication is implementation specific.
NOTE 1: The Suspension of traffic duplication can be caused by e.g. the locally detected UPF congestion. In that way the UPF can stop receiving duplicated traffic via 3GPP and non-3GPP access network simultaneously.
The UPF may indicate in the PMF-Suspend Duplication Request message the type of traffic (i.e. GBR or non-GBR) for which traffic duplication is being suspended. The PMF-Suspend Duplication Request message is sent over the user plane of any available access network of the MA PDU Session. Once the UE receives the PMF-Suspend Duplication Request message from the UPF, the UE shall stop duplicating the type of traffic for which traffic duplication is suspended.
If the UPF does not provide the type of traffic (GBR or non-GBR) in the PMF-Suspend Duplication Request message, traffic duplication is suspended for all traffic for which traffic duplication is being performed. Once UPF suspended traffic duplication and if no Primary Access is configured, both the UE and the UPF decide, based on their own implementation, which access network to use for sending UL and DL traffic. If the Primary Access is configured, both the UE and the UPF use the Primary Access for sending UL and DL traffic.
The UPF may decide to resume traffic duplication for a UE by sending the PMF-Resume Duplication Request message. How the UPF determines to resume traffic duplication is implementation specific.
NOTE 2: Traffic duplication can be resumed e.g. when the UPF has detected that local congestion has diminished.
Once the UE receives the PMF-Resume Duplication Request message from the UPF, the UE may restart to duplicate the type of traffic for which traffic duplication is resumed based on the provided Redundant steering mode policies and UE implementation.