5.27.2.5.2 Proactive RAN feedback for adaptation of Burst Arrival Time and Periodicity

If the NG-RAN receives a Burst Arrival Time and Burst Arrival Time Window in the TSCAI for a QoS Flow, the 5GS will perform the following actions:

• The NG-RAN can determine a BAT offset in order to align the expected arrival of the traffic bursts (as indicated in the BAT) with the time when the next transmission over the air interface in each direction (i.e. DL or UL) is expected. The BAT offset shall always be provided by NG-RAN and it shall be within the BAT Window. The BAT offset is calculated with reference to the BAT.
• If the BAT offset is provided from NG-RAN to the SMF in the response to the QoS Flow establishment or modification request, the SMF provides the BAT offset to the PCF and the PCF notifies the AF as described in clause 6.1.3.23a of TS 23.503 [45]. The SMF also updates the BAT value of the locally stored TSCAI based on the received BAT offset.

NOTE 1: SMF updates the locally stored TSCAI so that after a handover SMF provides the updated BAT (adjusted by the BAT offset) to the target NG-RAN node.

• The SMF may adjust the BAT offset received from NG-RAN based on the clock drifting report from UPF as specified in clause 4.4.3.4 of TS 23.502 [3].

NOTE 2: The feedback from RAN implies that the RAN accepts the BAT offset. If the AF requested BAT is acceptable for NG-RAN, the NG-RAN provides a BAT offset of zero.

• If the RAN also receives a Periodicity Range along with the Periodicity in the TSCAI for a QoS flow, the 5GS will further perform the following actions:
• The RAN may determine an adjusted periodicity in order to align the periodicity of the traffic bursts with the expected time interval between subsequent transmission opportunities over the air interface in each direction (i.e. DL or UL). If the RAN determines an adjusted periodicity, the RAN provides it together with a BAT offset mentioned above. The adjusted periodicity shall be within the Periodicity Range and the BAT offset is based on the adjusted periodicity.
• The adjusted periodicity is forwarded to the AF via the SMF and the PCF together with a BAT offset in the same way it is described above. The SMF also updates the periodicity value of the locally stored TSCAI based on the received adjusted periodicity.

NOTE 3: SMF updates the locally stored TSCAI so that after a handover SMF provides the adjusted periodicity to the target NG-RAN node.

• If interworking with a TSN network deployed in the transport network is supported, the SMF/CUC uses the adjusted periodicity (if provided) and BAT offset accepted by the RAN to adjust the related parameters in the Talker/Listener Group and the Talker/Listener Group is as described in Annex M, clause M.1. How the related parameters are adjusted is left to the implementation.