Section: 10.11.1 EN-DC
Content: The secondary RAT data volume reporting function is used to report the data volume of secondary RAT to CN. In EN-DC, if configured, the MN reports the uplink and downlink data volumes of used NR resources to the EPC on a per EPS bearer basis as specified in TS 36.300[ Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 ]  [2]. Periodic reporting is performed by periodically sending the Secondary RAT Data Usage Report messages to the MME. The data volume is counted by the node hosting PDCP. Downlink data volume is counted in bytes of PDCP SDUs successfully delivered to the UE over NR (for RLC AM) or transmitted to the UE over NR (for RLC UM). Uplink data volume is counted in bytes of PDCP SDUs received by the node hosting PDCP over NR. Forwarded packets shall not be counted when PDCP entity is relocated. When PDCP duplication is activated, packets shall be counted only once. Figure 10.11.1-1: Secondary RAT data volume periodic reporting - EN-DC Figure 10.11.1-1 shows an example signalling flow for secondary RAT data volume periodic reporting: 1. If the 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 NR radio resources for the related SN-terminated E-RABs. 2. The MN sends the Secondary RAT Data Usage Report message to MME to provide information on the used NR resource. NOTE: The Secondary RAT Data Usage Report message sent by the MN may also include secondary RAT report information of MN-terminated bearers.