Section: 5.32.5.2 Round Trip Time Measurements
Content: RTT measurements can be conducted by the UE and UPF independently. There is no measurement reporting from one side to the other. RTT measurements are defined to support the "Smallest Delay", "Priority-based", "Load Balancing" or "Redundant" steering mode (i.e. when RTT threshold value is applied). The estimation of the RTT by the UE and by the UPF is based on the following mechanism: 1. The PMF in the UE sends over the user plane PMF-Echo Request messages to the PMF in the UPF, and the PMF in the UPF responds to each one with a PMF-Echo Response message. Similarly, the PMF in the UPF sends over the user plane PMF-Echo Request messages to the PMF in the UE, and the PMF in the UE responds to each one with a PMF-Echo Response message. 2. When the UP connection of the MA PDU session is deactivated on an access, no PMF-Echo Request messages are sent on this access. The PMF in the UPF shall not send PMF-Echo Request on this access if the UP connection is not available or after it receives notification from the (H-)SMF to stop sending the PMF-Echo Request on this access. 3. The UE and the UPF derive an estimation of the average RTT over an access type and QoS Flow by averaging the RTT measurements obtained over this access type and QoS Flow.