Section: 10.10.1 EN-DC
Content: The RRC Transfer procedure is used to deliver an RRC message, encapsulated in a PDCP PDU between the MN and the SN (and vice versa) so that it may be forwarded to/from the UE using split SRB. The RRC transfer procedure is also used for: - providing an NR measurement report, NR failure information, NR UE assistance information or intra-SN CPC execution completion from the UE to the SN via the MN. If UE is IAB-MT, providing NR IAB other information from the IAB-MT to the SN via the MN; - providing MCG failure information from the UE to the MN via the SN and an RRC reconfiguration, or release, or an inter-RAT handover command from the MN to the UE via the SN. Additional details of the RRC transfer procedure are defined in TS 36.423[ Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 Application Protocol (X2AP) ]  [9]. Split SRB: Figure 10.10.1-1: RRC Transfer procedure for the split SRB (DL operation) Figure 10.10.1-1 shows an example signaling flow for the DL RRC Transfer in case of the split SRB: 1. The MN, when it decides to use the split SRBs, starts the procedure by initiating the RRC Transfer procedure. The MN encapsulates the RRC message in a PDCP-C PDU and ciphers with own keys. NOTE: The usage of the split SRBs shall be indicated in the Secondary Node Addition procedure or Modification procedure. 2. The SN forwards the RRC message to the UE. 3. The SN may send PDCP delivery acknowledgement of the RRC message forwarded in step 2. Figure 10.10.1-2: RRC Transfer procedure for the split SRB (UL operation) Figure 10.10.1-2 shows an example signaling flow for the UL RRC Transfer in case of the split SRB: 1. When the UE provides response to the RRC message, it sends it to the SN. 2. The SN initiates the RRC Transfer procedure, in which it transfers the received PDCP-C PDU with encapsulated RRC message. NR measurement report, NR failure information, NR UE assistance information, NR IAB other information or intra-SN CPC execution completion: Figure 10.10.1-3: RRC Transfer procedure for NR measurement report, NR failure information, NR UE assistance information, NR IAB other information or intra-SN CPC execution completion Figure 10.10.1-3 shows an example signaling flow for RRC Transfer in case of the forwarding of the NR measurement report, NR failure information, NR IAB other information from the UE, NR UE assistance information or intra-SN CPC execution completion: 1. When the UE sends a measurement report, NR failure information, NR UE assistance information, NR IAB other information or intra-SN CPC execution completion, it sends it to the MN in a container within ULInformationTransferMRDC message as specified in TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [10]. 2. The MN initiates the RRC Transfer procedure, in which it transfers the received NR measurement report, NR failure information, NR UE assistance information, NR IAB other information or intra-SN CPC execution completion as an octet string. MCG failure information and RRC Reconfiguration / RRC Release / inter-RAT handover command over SRB3: Figure 10.10.1-4: RRC Transfer procedure for MCG failure information Figure 10.10.1-4 shows an example signaling flow for RRC Transfer in case of the forwarding of the MCG failure information from the UE: 1. When the UE sends EUTRA MCGFailureInformation message over SRB3, it sends it to the SN in a container within ULInformationTransferMRDC message as specified in TS 38.331[ NR; Radio Resource Control (RRC); Protocol specification ]  [4]. 2. The SN initiates the RRC Transfer procedure, in which it transfers the received EUTRA MCGFailureInformation message as an octet string. 3. The MN initiates the RRC Transfer procedure, in which it transfers the EUTRA RRCConnectionReconfiguration message, or EUTRA RRCConnectionRelease message, or MobilityFromEUTRACommand message as an octet string. 4. The SN sends the received EUTRA RRC message to the UE over SRB3 in a container within DLInformationTransferMRDC, message as specified in TS 38.331[ NR; Radio Resource Control (RRC); Protocol specification ]  [4].