Content for  TS 38.300  Word version:  19.0.0

This clause describes the functionalities for the support of eXtended Reality (XR) services that require high data rate and low latency communications. An overview of XR services is available in TR 38.835, while the service requirements are documented in TS 22.261. Please note however that some of those functionalities need not be limited to the provision of XR services.

XR-Awareness relies on QoS flows, PDU Sets, Data Bursts and traffic assistance information (see TS 23.501). The following PDU Set QoS Parameters may be provided by the SMF to the gNB as part of the QoS profile of the QoS flow:

• PDU Set Delay Budget (PSDB): as defined in TS 23.501, upper bound for the duration between the reception time of the first PDU (at the UPF for DL, at the UE for UL) and the time when all PDUs of a PDU Set have been successfully received (at the UE in DL, at the UPF in UL). When available, supersedes the PDB of the QoS flow.
• PDU Set Error Rate (PSER): as defined in TS 23.501, upper bound for a rate of non-congestion related PDU Set losses between RAN and the UE. When available, it supersedes the PER of the QoS flow.
• PDU Set Integrated Handling Information (PSIHI): indicates whether all PDUs of the PDU Set are needed for the usage of PDU Set by application layer, as defined in TS 23.501.
  The PDU Set based handling can be enabled based on the PDU Set QoS Parameters, or based on the DL PDU Set Information Marking Support Indication received from SMF.

During the Xn-handover preparation procedure, the source gNB sends the stored PDU Set QoS Parameters as part of the QoS profile to the target NG-RAN node. For NG handover, the AMF provides the PDU Set QoS parameters to the target gNB by means of the NGAP HANDOVER REQUEST message. The UPF can identify PDUs that belong to PDU Sets, and may indicate to the gNB the following PDU Set Information in the GTP-U header:

• PDU Set Sequence Number;
• Indication of End PDU of the PDU Set;
• PDU Sequence Number within a PDU Set;
• PDU Set Size in bytes;
• PDU Set Importance (PSI), which identifies the relative importance of a PDU Set compared to other PDU Sets within the same QoS Flow.

5GC may provide XR traffic assistance information to gNB through NG AP TSC Assistance Information (TSCAI) as specified in clause 5.37.8 of TS 23.501 (for both GBR and non-GBR QoS flows):

• UL and/or DL Periodicity;
• N6 Jitter Information (i.e. between UPF and Data Network) associated with the DL Periodicity.

This assistance information can be used by the gNB to configure DRX to enable better UE power saving. In addition, 5GC may provide the following information through NG-U as specified in clause 5.37.5.2 of TS 23.501:

• Indication of End of Data Burst in the GTP-U header of the last PDU in downlink:
  • this information can be used by the gNB to push the UE back to sleep when possible.
• Indication of Data Burst Size in the GTP-U header of the first PDUs of the data burst in downlink: this information can be used by the gNB to assist radio resource management.
• Indication of Time To Next Burst in the GTP-U header in downlink: this information represents the interval between the transmission of the last PDU in the current data burst and the first PDU of the next data burst, and can be used by the gNB to assist scheduling in downlink.

During the data forwarding for handover, the source gNB provides the Indication of End of Data Burst, Indication of Data Burst Size, and Time to Next Burst received from the UPF to target gNB in case one or more PDUs of the data burst is forwarded to target gNB. Finally, 5GC may provide the Multi-modal Service ID (MMSID) to NG-RAN, as part of the QoS parameters of the QoS flow, when establishing and/or updating the corresponding QoS Flows. It is up to the gNB's implementation to use this information for multi-modality service. In the uplink, the UE needs to be able to identify PDU Sets and Data Bursts dynamically, including PSI. How this is done is left up to UE implementation but when possible for a QoS flow, this is indicated to the gNB via UE Assistance Information.

Most XR video frame rates (15, 30, 45, 60, 72, 90 and 120 fps) correspond to periodicities that are not an integer (66.66, 33.33, 22.22, 16.66, 13.88, 11.11 and 8.33 ms respectively). The gNB may configure a DRX cycle expressed in rational numbers so that the DRX cycle matches those periodicities, e.g. for the traffic with a frame rate of 60 fps, the network may configure the UE with a DRX cycle of 50/3 ms. Configured grants may be configured without the need for the UE to wake up to monitor possible grants for UL retransmissions of configured grants, thus increasing the number of power saving opportunities for the UE.

During a handover from a gNB supporting PDU Set based handling to another gNB, the source gNB signals the PDU Set Information over Xn-U if the target node has signalled the support of PDU Set based handling in the Xn Handover Request Acknowledge message. During a handover, transition from RRC_INACTIVE to RRC_CONNECTED or RRC re-establishment from a gNB not supporting PDU Set based handling to a gNB supporting PDU Set based handling, the target/new serving gNB may indicate the support of PDU Set based handling to the SMF during the Path Switch Request procedure or Handover Resource Allocation procedure (in case of NG handover), the SMF will act as specified in TS 23.501. If the indication is absent, the SMF infers that PDU Set based handling is not supported by the target/new serving gNB node, then the SMF will act as specified in TS 23.501. During a handover, transition from RRC_INACTIVE to RRC_CONNECTED or RRC re-establishment from a gNB node not supporting PDU Set based handling to a gNB node supporting PDU Set based handling, the target/new serving gNB node may receive unmarked PDU(s) (i.e. PDU(s) without PDU Set Information Container) forwarded from the source/last serving gNB, node and marked PDU(s) (i.e. PDU(s) with PDU Set Information Container) from UPF, how the target/new serving gNB node handles the marked and unmarked PDUs for the same QoS flow is up to implementation.

To enable the transmission and reception during some of the measurements gaps configured for RRM measurements, a measurement gap occasion may be cancelled via DCI. In addition, the UE may provide, via UE Assistance information, a recommended gap occasion cancellation ratio per measurement gap configuration.