8.7.12 RRC Transfer

36.4233GPPEvolved Universal Terrestrial Radio Access Network (E-UTRAN)Release 17TSX2 Application Protocol (X2AP)

8.7.12.1 General

The purpose of the RRC Transfer procedure is to deliver a PDCP-C PDU encapsulating an LTE RRC message to the en-gNB so that it may then be forwarded to the UE, or from the en-gNB, if it was received from the UE. Delivery status may also be provided from the en-gNB to the MeNB using the RRC Transfer.

The procedure is also to enable transfer of the NR RRC message container with the NR measurements from the MeNB to the en-gNB, when received from the UE.

The procedure is also to enable transfer of the NR RRC message container with the NR failure information from the MeNB to the en-gNB, when received from the UE.

The procedure is also used to enable transfer of the NR RRC message container with an IAB information from the MeNB to the en-gNB, when received from the IAB-MT.

The procedure is also to enable transfer of the NR RRC message container with the NR RRCReconfigurationComplete message from the MeNB to the en-gNB, when received from the UE.

The procedure is also to enable transfer of the NR RRC message container with the UE Assistance information from the MeNB to the en-gNB, when received from the UE.

The procedure uses UE-associated signalling.

8.7.12.2 Successful Operation

Figure 8.7.12.2-1: RRC Transfer procedure, successful operation.

Either the MeNB initiates the procedure by sending the RRC TRANSFER message to the en-gNB or the en-gNB initiates the procedure by sending the RRC TRANSFER message to the MeNB.

If the en-gNB receives an RRC TRANSFER message which does not include the RRC Container IE in the Split SRB IE, or the RRC container IE in NR UE Report IE, or the RRC Container IE in the Fast MCG Recovery via SRB3 from MN to SN IE, or the RRC Container IE in the Fast MCG Recovery via SRB3 from SN to MN IE, it shall ignore the message. If the en-gNB receives an RRC TRANSFER message with the Delivery Status IE, it shall ignore the message. If the en-gNB receives the RRC Container IE in the Split SRB IE, it shall deliver the contained PDCP-C PDU encapsulating an RRC message to the UE. If the en-gNB receives the RRC Container IE in the Fast MCG Recovery from MeNB to SgNB IE, the en-gNB shall, if supported, deliver the contained RRC Container encapsulating an RRC message to the UE.

If the MeNB receives the Delivery Status IE in the split SRB IE the MeNB shall consider RRC messages up to the indicated NR PDCP SN as having been successfully delivered (as defined in TS 36.322 [40]) to the UE by the en-gNB. If the MeNB receives the RRC Container IE in the Fast MCG Recovery from SgNB to MeNB IE, the MeNB shall, if supported, consider MCG link failure detected at the UE as specified in TS 37.340 [32].

8.7.12.3 Abnormal Conditions

In case of the split SRBs, the receiving node may ignore the message, if the MeNB has not indicated possibility of RRC transfer at the bearer setup.