Section: 10.11.2 MR-DC with 5GC
Content: The secondary RAT data volume reporting function is used to report the data volume of secondary RAT to the 5GC. In MR-DC with 5GC, if configured, the MN reports the uplink and downlink data volumes of used secondary RAT resources to the 5GC as specified in TS 23.501[ System architecture for the 5G System (5GS) ]  [11]. Configuration for reporting of secondary RAT data volume may happen separately for NR and E-UTRA. Secondary RAT data volume reporting indicates the secondary RAT type. For each PDU session, it contains data volumes consumed for the whole PDU Session, or for selected QoS flow, or both. Periodic reporting is performed by periodically sending the Secondary RAT Data Usage Report messages to the 5GC. The data volume is counted by the node hosting PDCP. Downlink data volume is counted in bytes of SDAP SDUs successfully delivered to the UE (for RLC AM) or transmitted to the UE (for RLC UM). Uplink data volume is counted in bytes of SDAP SDUs received by the node hosting PDCP. Forwarded packets shall not be counted when PDCP entity is relocated. When PDCP duplication is activated, packets shall be counted only once. Figure 10.11.2-1: Secondary RAT data volume periodic reporting - MR-DC with 5GC Figure 10.11.2-1 shows an example signalling flow for secondary RAT data volume periodic reporting: 1. For SN terminated bearers, the SN sends the Secondary RAT Data Usage Report message to the MN and includes the data volumes of used secondary RAT resources for PDU Sessions or selected QoS flows or both mapped to SN-terminated bearers. If periodic reporting is configured, then the SN periodically sends the Secondary RAT Data Usage Report message to the MN and includes the data volumes of used radio resources. 2. The MN sends the Secondary RAT Data Usage Report message to the 5GC to provide information on the used radio resources. NOTE: The Secondary RAT Data Usage Report message sent by the MN may also include secondary RAT data volumes of used secondary RAT resources for MN terminated bearers.