Section: 7.7 SCG/MCG failure handling
Content: RLF is declared separately for the MCG and for the SCG. If radio link failure is detected for MCG, fast MCG link recovery is configured and the SCG is not deactivated, the UE triggers fast MCG link recovery. Otherwise, the UE initiates the RRC connection re-establishment procedure. During the execution of PSCell addition or PSCell change, if radio link failure is detected for MCG, the UE initiates the RRC connection re-establishment procedure. During fast MCG link recovery, the UE suspends MCG transmissions for all radio bearers, except SRB0, and, if any, BH RLC channels and reports the failure with MCGFailureInformation message to the MN via the SCG, using the SCG leg of split SRB1 or SRB3. The UE includes in the MCGFailureInformation message the measurement results available according to current measurement configuration of both the MN and the SN. Once the fast MCG link recovery is triggered, the UE maintains the current measurement configurations from both the MN and the SN, and continues measurements based on configuration from the MN and the SN, if possible. The UE initiates the RRC connection re-establishment procedure if it does not receive an RRCConnectionReconfiguration message, RRCReconfiguration message, MobilityFromNRCommand message, MobilityFromEUTRACommand message, RRCConnectionRelease message or RRCRelease message within a certain time after fast MCG link recovery was initiated. Upon reception of the MCGFailureInformation message, the MN can send RRCConnectionReconfiguration message, RRCReconfiguration message, MobilityFromNRCommand message, MobilityFromEUTRACommand message, RRCConnectionRelease message or RRCRelease message to the UE, using the SCG leg of split SRB1 or SRB3. Upon receiving an RRCConnectionReconfiguration message, RRCReconfiguration message, MobilityFromNRCommand message or MobilityFromEUTRACommand message, the UE resumes MCG transmissions for all radio bearers. Upon receiving an RRCConnectionRelease message or RRCRelease message, the UE releases all the radio bearers and configurations. NOTE 1: It is up to network implementation to guarantee that the RRC-related messages are delivered to the UE by the SN before the release of its control plane resources. The following SCG failure cases are supported: - SCG RLF; - SCG beam failure while the SCG is deactivated; - SN addition/change failure; - For EN-DC, NGEN-DC and NR-DC, SCG configuration failure or CPC configuration failure (only for messages on SRB3); - For EN-DC, NGEN-DC and NR-DC, SCG RRC integrity check failure (on SRB3); - For EN-DC, NGEN-DC and NR-DC, consistent UL LBT failure on PSCell; - For IAB-MT, reception of a BH RLF indication from SCG; - CPA/CPC or subsequent CPAC execution failure; - SCG LTM cell switch failure. Upon SCG failure, if MCG transmissions of radio bearers are not suspended, the UE suspends SCG transmissions for all radio bearers and, if any, BH RLC channels, if the SCG failure is not triggered by SCG beam failure, and reports the SCGFailureInformation to the MN, instead of triggering re-establishment. If SCG failure is detected while MCG transmissions for all radio bearers are suspended, the UE initiates the RRC connection re-establishment procedure. SCG/MCG failure handling by UE also applies to IAB MT. In all SCG failure cases, the UE maintains the current measurement configurations from both the MN and the SN and the UE continues measurements based on configuration from the MN and the SN if possible. The SN measurements configured to be routed via the MN will continue to be reported after the SCG failure. NOTE 2: UE may not continue measurements based on configuration from the SN after SCG failure in certain cases (e.g. UE cannot maintain the timing of PSCell). The UE includes in the SCGFailureInformation message the measurement results available according to current measurement configuration of both the MN and the SN. The MN handles the SCGFailureInformation message and may decide to keep, change, or release the SN/SCG. In all the cases, the measurement results according to the SN configuration and the SCG failure type may be forwarded to the old SN and/or to the new SN. In case of CPA/CPC, upon transmission of the SCGFailureInformation message to the MN, the UE stops evaluating the CPA/CPC execution condition. In case of subsequent CPAC, upon transmission of the SCGFailureInformation message to the MN or upon transmission of the MCGFailureInformation message to the SN, the UE stops evaluating the subsequent CPAC execution condition. The UE is not required to continue measurements for candidate PSCell(s) for execution condition upon transmission of the SCGFailureInformation message to the MN.