Improvements in and relating to L1 / L2-triggered mobility (LTM) in a telecommunication network

Abstract

A method of performing L1 / L2 Triggered Mobility (LTM) in a User Equipment (UE) connected in a Dual Connectivity (DC) configuration to a Master Node (MN) or Master Cell Group (MCG) and a Secondary Node

Description

The present invention relates to improvements in L1 / L2-Triggered Mobility (LTM) in a telecommunication network. Embodiments of the invention aim to provide solutions to support LTM with low latency, low complexity and no user plane data loss. Embodiments also aim to take into account the impact on legacy behaviours to avoid conflicts therewith. More particularly, embodiments aim to provide methods to support LTM cell switch for a User Equipment (UE) configured with dual connectivity, e.g. LTM cell switch for Secondary Cell Group (SCG). Embodiments also aim to provide several solutions to handle failure cases for LTM execution in order to recover quickly. Further, embodiments aim to address shortcomings in the prior art, whether mentioned herein or not. According to the present invention there is provided an apparatus and method as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows. According to a first aspect of the present invention, there is provided a method of performing L1 / L2 Triggered Mobility, LTM, in a User Equipment, UE, communicatively connected in a Dual Connectivity , DC, configuration to a Master Node, MN, or master Cell Group, MCG, and a Secondary Node, SN, or Secondary Cell Group, SCG, wherein: if LTM is triggered for the MN or MCG, then the UE maintains MCG Cell-Radio Network Temporary Identifier, C-RNTI, and clears or releases other current dedicated radio configurations associated with a cell group for which the LTM procedure is triggered; or if LTM is triggered for the SN or SCG, then the UE clears or releases current dedicated radio configuration associated with a cell group for which the LTM procedure is triggered In an embodiment, if LTM is triggered for the MN or MCG, then one of the other current dedicated radio configurations associated with a cell group for which the LTM procedure is triggered includes SCG C-RNTI. In an embodiment, if LTM is triggered for the SN or SCG, then conditions for parameters set in an RRC message and instructions of a lower layer are satisfied only to trigger a random access procedure. In an embodiment, upon receipt of an RRCReconfiguration message by the UE, determining if scg-State is included in the RRCReconfiguration message and if not, determining if reconfigurationWihSync is included in spCellConfig in nr-SCG and if the RRCReconfiguration message is not applied due to an LTM cell switch execution for which a lower layer indicates to skip the Random Access procedure, then initiate a Random Access procedure on the PSCell. According to a second aspect of the present invention, there is provided apparatus arranged to perform the method of the first aspect. Although a few preferred embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims. For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example only, to the accompanying diagrammatic drawings in which: Figure 1 shows a signalling procedure for LTM; Figure 2 shows a network configuration relevant to an embodiment of the invention; and Figure 3 shows a flowchart illustrating an embodiment of the invention. The procedure for LTM, as shown with reference to Figure 1 is as follows. 1. The UE sends a MeasurementReport message to the gNB. The gNB decides to use LTM and initiates candidate cell(s) preparation. 2. The gNB transmits an RRCReconfiguration message to the UE including the LTM candidate cell configurations of one or multiple candidate cells. 3. The UE stores the LTM candidate cell configurations and transmits a RRCReconfigurationComplete message to the gNB. 4a. The UE may perform DL synchronization with candidate cell(s) before receiving the cell switch command. DL synchronization for candidate cell(s) before cell switch command can be supported, at least based on SSB. 4b. The UE may perform early TA acquisition with candidate cell(s) requested by the network before receiving the cell switch command. This is done via Random access procedure (i.e. Contention-Free Random Access procedure, CFRA) triggered by a PDCCH order from the source cell, following which the UE sends preamble towards the indicated candidate cell. In order to minimize the data interruption of the source cell due to CFRA towards the candidate cell(s), the UE doesn’t receive RAR for the purpose of TA value acquisition and the TA value of the candidate cell is indicated in the cell switch command. The UE doesn’t maintain the TA timer for the candidate cell and relies on network implementation to guarantee the TA validity. Synchronization for candidate cell(s) before cell switch command is supported, at least based on SSB. TA acquisition of candidate cell(s) before LTM cell switch command is supported, at least based on PDCCH ordered RACH, where the PDCCH order is only triggered by source cell. The source cell can trigger UE’s RACH (Random Access Procedure) toward a candidate cell by PDCCH order to acquire TA(Timing Advance or Timing Advance value) for the candidate cell, which only performs preamble transmission and does not expect the reception of RAR (Random Access Response) to ease network implementation and UE implementation. Specifically, the preamble transmission during this RACH(Random Access procedure) for TA acquisition (i.e. early RACH) can be considered as this Random Access procedure is successfully completed. To reduce the processing complexity, UE does not have to calculate RA-RNTI (RNTI(Radio Network Temporary Identifier) for Random Access Response) before / when the preamble is transmitted, unlike normal Random Access procedure (RACH). To be more specific, UE transmits preamble to a candidate cell as indicated by PDCCH order. The network (or DU(Distributed Unit) or the candidate cell) calculates the TA (Timing Advance). The source cell / DU can get the calculated TA from the candidate cell / DU. By doing this RACH(Random Access procedure) for TA acquisition (i.e. early RACH), the network can have the TA values for the candidate cells and knows whether these TAs are still valid or not, e.g., by maintaining a network side timer (i.e. TAT(timeAlignmentTimer) for each TA value or each candidate cell). In this way, the source cell / DU gets to know the value and the validity of candidate cell TA. The source cell / DU needs to know whether a candidate cell TA is still valid because the source cell / DU needs to determine whether it can initiate a RACH-less solution for LTM cell switch and then determine whether it needs to include a beam indication (e.g.TCI state) and TA information in the LTM MAC CE. Therefore, the network can indicate a valid TA to the UE or indicate whether a TA is still valid in LTM MAC CE. The UE may not need to maintain a TA timer for candidate cells, which simplifies UE implementation. Upon the reception of the TA information indicated in LTM MAC CE, the UE can apply the TA value and start the TA timer for the target LTM candidate cell upon LTM execution (i.e. LTM cell switch) and UE can perform LTM cell switch without Random access procedure (i.e. with RACH-less solution to skip the Random access procedure) if TAT for the target LTM candidate cell is running (i.e. TA value is vaild) or if Beam failure is not detected for the target LTM candidate cell, which means that UE can monitor PDCCH from the target LTM candidate cell or UE can use configured grants the first UL data transmission to the target cell for RACH-less LTM execution (LTM cell switch). 5. The UE performs L1 measurements on the configured candidate cell(s), and transmits lower-layer measurement reports to the gNB. 6. The gNB decides to execute cell switch to a target cell, and transmits a MAC CE triggering cell switch by including the candidate configuration index of the target cell. The UE switches to the configuration of the target cell. 7. The UE performs random access procedure towards the target cell, if cell switch needs to include performing random access procedure. 8. The UE completes the LTM cell switch procedure by sending RRCReconfigurationComplete message to target cell. If the UE has performed a RA procedure in step 7, the UE considers that LTM execution is successfully completed when the random access procedure is successfully completed. For RACH-less LTM, the UE considers that LTM execution is successfully completed when the UE determines that the network has successfully received its first UL data. The UE determines successful reception of its first UL data by receiving a PDCCH addressing the UE’s C-RNTI in the target cell, which schedules a new transmission following the first UL data. The UE can perform the steps 4-8 multiple times for subsequent LTM cell switch based on the configuration provided in step 2. The LTM cell switch procedure has mainly been designed for UEs configured with a single connectivity, i.e. a single connection with one gNB. In New Radio (NR), having UEs configured with dual connectivity (DC) is common due to the coexistence of Long Term Evolution (LTE) and NR and the high requirement on data rate and low latency, i.e. two connections are provided for the UE, with MCG (Master Cell Group or MN (Master Node)) and SCG (Secondary Cell Group or SN (Secondary Node)). In general, a UE has different Radio Resource Control (RRC) procedures towards MCG and SCG, separately. Figure 2 shows a generic view of a DC configured network, including NR-gNB and LTE eNB and associated network components, as well as a UE. In an embodiment of the present invention, a UE is configured with dual connectivity, i.e. LTM cell switch procedure is supported for MCG and SCG, independently, and several solutions are described to achieve this. Firstly, the MCG should not be involved in LTM cell switch procedure for SCG to make it simple. However, given that SCG configuration can be sent via SRB1 (i.e. MCG), the UE should avoid triggering the corresponding actions related to SCG parameters if the parameters are received from MCG. One of the critical parameters is “reconfigurationwithsync”, which automatically triggers a random access (RA) procedure in SCG Medium Access Control (MAC) entity. To avoid this unintended behaviour, conditions relating to LTM candidate configuration and associated procedure follow later. In addition to this, the UE keeps MCG Cell-Radio Network Temporary Identifier (C-RNTI) upon LTM cell switch execution for MCG while the UE releases SCG C-RNTI upon LTM cell switch execution for SCG to save UE memory. This is because MCG C-RNTI may be used at RLF (Radio Link Failure) or RRC Re-establishment but it is not worth keeping SCG C-RNTI, as set out later. The following relates to RRC Reconfiguration. The purpose of this procedure is to modify an RRC connection, e.g. to establish / modify / release RBs / BH RLC channels / Uu Relay RLC channels / PC5 Relay RLC channels, to perform reconfiguration with sync, to setup / modify / release measurements, to add / modify / release SCells and cell groups, to add / modify / release conditional handover configuration, to add / modify / release conditional PSCell change or conditional PSCell addition configuration, to add / modify / LTM candidate cells. As part of the procedure, NAS dedicated information may be transferred from the Network to the UE. RRC reconfiguration to perform reconfiguration with sync includes, but is not limited to, the following cases: reconfiguration with sync and security key refresh, involving RA to the Pcell / PSCell, MAC reset, refresh of security and re-establishment of RLC and PDCP triggered by explicit L2 indicators; reconfiguration with sync but without security key refresh, involving RA to the Pcell / PSCell, MAC reset and RLC re-establishment and PDCP data recovery (for AM DRB or AM MRB) triggered by explicit L2 indicators. reconfiguration with sync for DAPS and security key refresh, involving RA to the target Pcell, establishment of target MAC, and for non-DAPS bearer: refresh of security and re-establishment of RLC and PDCP triggered by explicit L2 indicators; for DAPS bearer: establishment of RLC for the target Pcell, refresh of security and reconfiguration of PDCP to add the ciphering function, the integrity protection function and ROHC function of the target Pcell; for SRB: refresh of security and establishment of RLC and PDCP for the target Pcell; reconfiguration with sync for DAPS but without security key refresh, involving RA to the target Pcell, establishment of target MAC, and for non-DAPS bearer: RLC re-establishment and PDCP data recovery (for AM DRB or AM MRB) triggered by explicit L2 indicators. for DAPS bearer: establishment of RLC for target Pcell, reconfiguration of PDCP to add the ciphering function, the integrity protection function and ROHC function of the target Pcell; for SRB: establishment of RLC and PDCP for the target Pcell. reconfiguration with sync for direct-to-indirect path switch, not involving RA at target side, involving re-establishment of PDCP / PDCP data recovery (for AM DRB) triggered by explicit L2 indicators. In (NG) EN-DC and NR-DC, SRB3 can be used for measurement configuration and reporting, for UE assistance (re-)configuration and reporting for power savings, for IP address (re-)configuration and reporting for lAB-nodes, to (re-)configure MAC, RLC, BAP, physical layer and RLF timers and constants of the SCG configuration, and to reconfigure PDCP for DRBs associated with the S-KgNB or SRB3, and to reconfigure SDAP for DRBs associated with S-KgNB in NGEN-DC and NR-DC, and to add / modify / release conditional PSCell change configuration, provided that the (re-)configuration does not require any MN involvement, and to transmit RRC messages between the MN and the UE during fast MCG link recovery. In (NG)EN-DC and NR-DC, only measConfig, radioBearerConfig, conditionalReconfiguration, bap-Config, iab-IP-AddressConfigurationList, otherConfig and / or secondaryCellGroup are included in RRCReconfiguration received via SRB3, except when RRCReconfiguration is received within DLlnformationTransferMRDC. The Network may initiate the RRC reconfiguration procedure to a UE in RRC_CONNECTED. The Network applies the procedure as follows: the establishment of RBs (other than SRB1, that is established during RRC connection establishment) is performed only when AS security has been activated; the establishment of BH RLC Channels for IAB is performed only when AS security has been activated; the establishment of Uu Relay RLC channels and PC5 Relay RLC channels (other than SL-RLCO and SL-RLC1) for L2 U2N Relay UE is performed only when AS security has been activated, and the establishment of PC5 Relay RLC channels for L2 U2N Remote UE (other than SL-RLCO and SL-RLC1) is performed only when AS security has been activated; the addition of Secondary Cell Group and SCells is performed only when AS security has been activated; the reconfigurationWithSync is included in secondaryCellGroup only when at least one RLC bearer or BH RLC channel is setup in SCG; the reconfigurationWithSync is included in masterCellGroup only when AS security has been activated, and SRB2 with at least one DRB or multicast MRB or, for IAB, SRB2, are setup and not suspended; the conditionalReconfiguration for CPC is included only when at least one RLC bearer is setup in SCG; the conditionalReconfiguration for CHO or CPA is included only when AS security has been activated, and SRB2 with at least one DRB or multicast MRB or, for IAB, SRB2, are setup and not suspended. the Itm-CandidateConfig (LTM candidate cell configuration) for LTM is included only when AS security has been activated, and SRB2 with at least one DRB are setup and not suspended. The UE shall perform the following actions upon reception of the RRCReconfiguration, or upon execution of the conditional reconfiguration (CHO, CPA or CPC): For LTM cell switch, how to generate the RRCReconfigurationComplete message is proposed in the following. Option 1. The RRCReconfigurationComplete message is generated upon the reception of LTM triggering MAC CE (or LTM cell switch execution) and then is sent to the target cell during LTM cell switch procedure (e.g. by Message 3 if random access procedure is performed or uplink data transmission if random access procedure is skipped (or not performed, i.e. RACH-less case). This Option 1 makes UE implementation simple because UE cannot know to which cell UE will perform LTM cell switch in advance. NOTE : To reduce the processing delay for generation of RRCReconfiguration complete, UE may generate the RRCReconfigurationComplete message for each LTM candidate cell configuration upon the reception of RRCReconfiguration message including the Itm-CandidateConfig (LTM candidate cell configuration) in advance, i.e. UE can decide to send one of RRCReconfiguationComplete messages based on the received LTM triggering MAC CE in MAC entity for LTM cell switch procedure. 1> if the LTM cell switch is triggered from lower layers (e.g. by receiving the LTM triggering MAC CE in MAC entity or LTM cell switch execution) or if the target LTM candidate cell configuration is applied due to a LTM candidate cell execution (In another embodiment, the second RRCReconfigurationComplete message can be generated when the LTM cell switch (LTM execution) is successfully completed.): 2> set the content of the RRCReconfigurationComplete message as follows: 3> include the LTM candidate cell configuration / information (e.g. cell identity or UE identity or configuration index or configuration identity) for the target cell indicated from lower layers (e.g. as indicated by LTM triggering MAC CE) NOTE : In case this procedure is initiated due to the generation of a complete LTM candidate cell configuration, the UE should generate only one RRCReconfigurationComplete message even if it process the LTM reference configuration and a LTM candidate cell configuration. The RRCReconfigurationComplete message includes the contents for the target cell indicated by LTM triggering MAC CE. 1> if the RRCReconfiguration message includes the Itm-CandidateConfig (LTM candidate cell configuration): 2> perform the LTM configuration procedure as specified in 3.3.1.3; 1> set the content of the RRCReconfigurationComplete message as follows if the RRCReconfiguration message does not include the Itm-CandidateConfig (LTM candidate cell configuration): NOTE : In case this procedure is initiated due to the generation of a complete LTM candidate cell configuration, the UE should generate only one RRCReconfigurationComplete message even if it process the LTM reference configuration and a LTM candidate cell configuration. The RRCReconfigurationComplete message includes the contents for the target cell indicated by LTM triggering MAC CE. 2> if the RRCReconfiguration includes the masterCellGroup containing the reportUplinkTxDirectCurrent: 3> include the uplinkTxDirectCurrentList for each MCG serving cell with UL; 3> include uplinkDirectCurrentBWP-SUL for each MCG serving cell configured with SUL carrier, if any, within the uplinkTxDirectCurrentList; 2> if the RRCReconfiguration includes the masterCellGroup containing the reportUplinkTxDirectCurrentTwoCarrier: 3> include in the uplinkTxDirectCurrentTwoCarrierList the list of uplink Tx DC locations for the configured intra-band uplink carrier aggregation in the MCG; 2> if the RRCReconfiguration includes the masterCellGroup containing the reportUplinkTxDirectCurrentMoreCarrier: 3> include in the uplinkTxDirectCurrentMoreCarrierList the list of uplink Tx DC locations for the configured intra-band uplink carrier aggregation in the MCG; 2> if the RRCReconfiguration includes the secondaryCellGroup containing the reportllplinkTxDirectCurrent: 3> include the uplinkTxDirectCurrentList for each SCG serving cell with UL; 3> include uplinkDirectCurrentBWP-SUL for each SCG serving cell configured with SUL carrier, if any, within the uplinkTxDirectCurrentList; 2> if the RRCReconfiguration includes the secondaryCellGroup containing the reportUplinkTxDirectCurrentTwoCarrier: 3> include in the uplinkTxDirectCurrentTwoCarrierList the list of uplink Tx DC locations for the configured intra-band uplink carrier aggregation in the SCG; 2> if the RRCReconfiguration includes the secondaryCellGroup containing the reportUplinkTxDirectCurrentMoreCarrier: 3> include in the uplinkTxDirectCurrentMoreCarrierList the list of uplink Tx DC locations for the configured intra-band uplink carrier aggregation in the SCG; NOTE Ob: The UE does not expect that the reportUplinkTxDirectCurrentTwoCarrier or reportUplinkTxDirectCurrentMoreCarrier is received in both masterCellGroup and in secondaryCellGroup. Network only configures at most one of reportUplinkTxDirectCurrent, reportUplinkTxDirectCurrentTwoCarrier or reportUplinkTxDirectCurrentMoreCarrier in one RRC message. 2> if the RRCReconfiguration message includes the mrdc-SecondaryCellGroupConfig with mrdc-SecondaryCellGroup set to eutra-SCG: 3> include in the eutra-SCG-Response the E-UTRA RRCConnectionReconfigurationComplete message in accordance with TS 36.331 clause 5.3.5.3; 2> if the RRCReconfiguration message includes the mrdc-SecondaryCellGroupConfig with mrdc-SecondaryCellGroup set to nr-SCG: 3> include in the nr-SCG-Response the SCG RRCReconfigurationComplete message; 3> if the RRCReconfiguration message is applied due to conditional reconfiguration execution and the RRCReconfiguration message does not include the reconfigurationWithSync in the masterCellGroup: 4> include in the selectedCondRRCReconfig the condReconfigld for the selected cell of conditional reconfiguration execution; 2> if the RRCReconfiguration includes the reconfigurationWithSync in spCellConfig of an MCG: 3> if the UE has logged measurements available for NR and if the RPLMN is included in plmn-ldentityList stored in VarLogMeasReport: 4> include the logMeasAvailable in the RRCReconfigurationComplete message; 4> if Bluetooth measurement results are included in the logged measurements the UE has available for NR: 5> include the logMeasAvailableBT in the RRCReconfigurationComplete message; 4> if WLAN measurement results are included in the logged measurements the UE has available for NR: 5> include the logMeasAvailableWLAN in the RRCReconfigurationComplete message; 3> if the sigLoggedMeasType in VarLogMeasReport is included: 4> if T330 timer is running and the logged measurements configuration is for NR: 5> set sigLogMeasConfigAvailable to true in the RRCReconfigurationComplete message; 4> else: 5> if the UE has logged measurements available for NR: 6> set sigLogMeasConfigAvailable to false in the RRCReconfigurationComplete message; 3> if the UE has connection establishment failure or connection resume failure information available in VarConnEstFailReport or VarConnEstFailReportList and if the RPLMN is equal to plmn-ldentity stored in VarConnEstFailReport or in at least one of the entries of VarConnEstFailReportList: 4> include connEstFaillnfoAvailable in the RRCReconfigurationComplete message; 3> if the UE has radio link failure or handover failure information available in VarRLF-Report and if the RPLMN is included in plmn-ldentityList stored in VarRLF-Report; or 3> if the UE has radio link failure or handover failure information available in VarRLF-Report of TS 36.331

[10] and if the UE is capable of cross-RAT RLF reporting and if the RPLMN is included in plmn-ldentityList stored in VarRLF-Report of TS 36.331

[10] : 4> include rlf-InfoAvailable in the RRCReconfigurationComplete message; 3> if the UE was configured with successHO-Config when connected to the source Pcell; and 3> if the applied RRCReconfiguration is not due to a conditional reconfiguration execution upon cell selection performed while timer T311 was running, as defined in 5.3.7.3: 4> perform the actions for the successful handover report determination as specified in clause 5.7.10.6, upon successfully completing the Random Access procedure triggered for the reconfigurationWithSync in spCellConfig of the MCG; 3> if the UE has successful handover information available in VarSuccessHO-Report and if the RPLMN is included in plmn-ldentityList stored in VarSuccessHO-Report: 4> include successHO-InfoAvailable in the RRCReconfigurationComplete message; 2> if the RRCReconfiguration message was received via SRB1, but not within mrdc-SecondaryCellGroup or E-UTRA RRCConnectionReconfiguration or E-UTRA RRCConnectionResume: 3> if the UE is configured to provide the measurement gap requirement information of NR target bands: 4> if the RRCReconfiguration message includes the needForGapsConfigNR; or 4> if the NeedForGapsInfoNR information is changed compared to last time the UE reported this information: 5> include the NeedForGapsInfoNR and set the contents as follows: 6> include intraFreq-needForGap and set the gap requirement information of intra-frequency measurement for each NR serving cell; 6> if requestedTargetBandFilterNR is configured: 7> for each supported NR band that is also included in requestedTargetBandFilterNR, include an entry in interFreq-needForGap and set the gap requirement information forthat band; 6> else: 7> include an entry in interFreq-needForGap and set the corresponding gap requirement information for each supported NR band; 3> if the UE is configured to provide the measurement gap and NCSG requirement information of NR target bands: 4> if the RRCReconfiguration message includes the needForGapNCSG-ConfigNR; or 4> if the needForGapNCSG-InfoNR information is changed compared to last time the UE reported this information: 5> include the NeedForGapNCSG-InfoNR and set the contents as follows: 6> include intraFreq-needForNCSG and set the gap and NCSG requirement information of intra-frequency measurement for each NR serving cell; 6> if requestedTargetBandFilterNCSG-NR is configured: 7> for each supported NR band included in requestedTargetBandFilterNCSG-NR, include an entry in interFreq-needForNCSG and set the NCSG requirement information forthat band; 6> else: 7> include an entry for each supported NR band in interFreq-needForNCSG and set the corresponding NCSG requirement information; 3> if the UE is configured to provide the measurement gap and NCSG requirement information of E UTRA target bands: 4> if the RRCReconfiguration message includes the needForGapNCSG-ConfigEUTRA; or 4> if the needForGapNCSG-InfoEUTRA information is changed compared to last time the UE reported this information: 5> include the NeedForGapNCSG-InfoEUTRA and set the contents as follows: 6> if requestedTargetBandFilterNCSG-EUTRA is configured, for each supported E-UTRA band included in requestedTargetBandFilterNCSG-EUTRA, include an entry in needForNCSG-EUTRA and set the NCSG requirement information for that band; otherwise, include an entry for each supported E-UTRA band in needForNCSG-EUTRA and set the corresponding NCSG requirement information; 2> if this procedure is initiated due to the generation of a complete LTM candidate cell configuration: 3> the procedure ends. Option 2. Upon the reception of RRCReconfiguation, RRCReconfiguationComplete is generated corresponding to the RRCReconfiguration, and sent to the source cell (serving cell or the current cell UE received the RRCReconfiguration from). Another RRCReconfigurationComplete message is generated upon the reception of LTM triggering MAC CE (or LTM cell switch execution) and then is sent to the target cell during LTM cell switch procedure (e.g. by Message 3 if random access procedure is performed or uplink data transmission if random access procedure is skipped (or not performed, i.e. RACH-less case). This Option 2 has the network know the successful delivery of RRCReconfiguration and makes UE implementation simple because UE cannot know to which cell UE will perform LTM cell switch in advance. NOTE : To reduce the processing delay for generation of RRCReconfiguration complete, UE may generate the RRCReconfigurationComplete message for each LTM candidate cell configuration upon the reception of RRCReconfiguration message including the Itm-CandidateConfig (LTM candidate cell configuration) in advance, i.e. UE can decide to send one of RRCReconfiguationComplete messages based on the received LTM triggering MAC CE in MAC entity for LTM cell switch procedure. 1> if the LTM cell switch is triggered from lower layers (e.g. by receiving the LTM triggering MAC CE in MAC entity or LTM cell switch execution) or if the target LTM candidate cell configuration is applied due to a LTM candidate cell execution (In another embodiment, the second RRCReconfigurationComplete message can be generated when the LTM cell switch (LTM execution) is successfully completed.): 2> set the content of the RRCReconfigurationComplete message as follows: 3> include the LTM candidate cell configuration / information (e.g. cell identity or UE identity or configuration index or configuration identity) for the target cell indicated from lower layers (e.g. as indicated by LTM triggering MAC CE) NOTE : In case this procedure is initiated due to the generation of a complete LTM candidate cell configuration, the UE should generate only one RRCReconfigurationComplete message even if it process the LTM reference configuration and a LTM candidate cell configuration. The RRCReconfigurationComplete message includes the contents for the target cell indicated by LTM triggering MAC CE. 1> if the RRCReconfiguration message includes the Itm-CandidateConfig (LTM candidate cell configuration): 2> perform the LTM configuration procedure as specified in 3.3.1.3; 2> set the content of the RRCReconfigurationComplete message as follows: NOTE : In case this procedure is initiated due to the generation of a complete LTM candidate cell configuration, the UE should generate only one RRCReconfigurationComplete message even if it process the LTM reference configuration and a LTM candidate cell configuration. The RRCReconfigurationComplete message includes the contents for the target cell indicated by LTM triggering MAC CE. 2> if the RRCReconfiguration includes the masterCellGroup containing the reportUplinkTxDirectCurrent: 3> include the uplinkTxDirectCurrentList for each MCG serving cell with UL; 3> include uplinkDirectCurrentBWP-SUL for each MCG serving cell configured with SUL carrier, if any, within the uplinkTxDirectCurrentList; 2> if the RRCReconfiguration includes the masterCellGroup containing the reportUplinkTxDirectCurrentTwoCarrier: 3> include in the uplinkTxDirectCurrentTwoCarrierList the list of uplink Tx DC locations for the configured intra-band uplink carrier aggregation in the MCG; 2> if the RRCReconfiguration includes the masterCellGroup containing the reportUplinkTxDirectCurrentMoreCarrier: 3> include in the uplinkTxDirectCurrentMoreCarrierList the list of uplink Tx DC locations for the configured intra-band uplink carrier aggregation in the MCG; 2> if the RRCReconfiguration includes the secondaryCellGroup containing the reportUplinkTxDirectCurrent: 3> include the uplinkTxDirectCurrentList for each SCG serving cell with UL; 3> include uplinkDirectCurrentBWP-SUL for each SCG serving cell configured with SUL carrier, if any, within the uplinkTxDirectCurrentList; 2> if the RRCReconfiguration includes the secondaryCellGroup containing the reportUplinkTxDirectCurrentTwoCarrier: 3> include in the uplinkTxDirectCurrentTwoCarrierList the list of uplink Tx DC locations for the configured intra-band uplink carrier aggregation in the SCG; 2> if the RRCReconfiguration includes the secondaryCellGroup containing the reportUplinkTxDirectCurrentMoreCarrier: 3> include in the uplinkTxDirectCurrentMoreCarrierList the list of uplink Tx DC locations for the configured intra-band uplink carrier aggregation in the SCG; NOTE Ob: The UE does not expect that the reportUplinkTxDirectCurrentTwoCarrier or reportUplinkTxDirectCurrentMoreCarrier is received in both masterCellGroup and in secondaryCellGroup. Network only configures at most one of reportUplinkTxDirectCurrent, reportUplinkTxDirectCurrentTwoCarrier or reportUplinkTxDirectCurrentMoreCarrier in one RRC message. 2> if the RRCReconfiguration message includes the mrdc-SecondaryCellGroupConfig with mrdc-SecondaryCellGroup set to eutra-SCG: 3> include in the eutra-SCG-Response the E-UTRA RRCConnectionReconfigurationComplete message in accordance with TS 36.331 clause 5.3.5.3; 2> if the RRCReconfiguration message includes the mrdc-SecondaryCellGroupConfig with mrdc-SecondaryCellGroup set to nr-SCG: 3> include in the nr-SCG-Response the SCG RRCReconfigurationComplete message; 3> if the RRCReconfiguration message is applied due to conditional reconfiguration execution and the RRCReconfiguration message does not include the reconfigurationWithSync in the masterCellGroup: 4> include in the selectedCondRRCReconfig the condReconfigld for the selected cell of conditional reconfiguration execution; 2> if the RRCReconfiguration includes the reconfigurationWithSync in spCellConfig of an MCG: 3> if the UE has logged measurements available for NR and if the RPLMN is included in plmn-ldentityList stored in VarLogMeasReport: 4> include the logMeasAvailable in the RRCReconfigurationComplete message; 4> if Bluetooth measurement results are included in the logged measurements the UE has available for NR: 5> include the logMeasAvailableBT in the RRCReconfigurationComplete message; 4> if WLAN measurement results are included in the logged measurements the UE has available for NR: 5> include the logMeasAvailableWLAN in the RRCReconfigurationComplete message; 3> if the sigLoggedMeasType in VarLogMeasReport is included: 4> if T330 timer is running and the logged measurements configuration is for NR: 5> set sigLogMeasConfigAvailable to true in the RRCReconfigurationComplete message; 4> else: 5> if the UE has logged measurements available for NR: 6> set sigLogMeasConfigAvailable to false in the RRCReconfigurationComplete message; 3> if the UE has connection establishment failure or connection resume failure information available in VarConnEstFailReport or VarConnEstFailReportList and if the RPLMN is equal to plmn-ldentity stored in VarConnEstFailReport or in at least one of the entries of VarConnEstFailReportList: 4> include connEstFaillnfoAvailable in the RRCReconfigurationComplete message; 3> if the UE has radio link failure or handover failure information available in VarRLF-Report and if the RPLMN is included in plmn-ldentityList stored in VarRLF-Report; or 3> if the UE has radio link failure or handover failure information available in VarRLF-Report of TS 36.331

[10] and if the UE is capable of cross-RAT RLF reporting and if the RPLMN is included in plmn-ldentityList stored in VarRLF-Report of TS 36.331 : 4> include rlf-InfoAvailable in the RRCReconfigurationComplete message; 3> if the UE was configured with successHO-Config when connected to the source Pcell; and 3> if the applied RRCReconfiguration is not due to a conditional reconfiguration execution upon cell selection performed while timer T311 was running, as defined in 5.3.7.3: 4> perform the actions for the successful handover report determination as specified in clause 5.7.10.6, upon successfully completing the Random Access procedure triggered for the reconfigurationWithSync in spCellConfig of the MCG; 3> if the UE has successful handover information available in VarSuccessHO-Report and if the RPLMN is included in plmn-ldentityList stored in VarSuccessHO-Report: 4> include successHO-InfoAvailable in the RRCReconfigurationComplete message; 2> if the RRCReconfiguration message was received via SRB1, but not within mrdc-SecondaryCellGroup or E-UTRA RRCConnectionReconfiguration or E-UTRA RRCConnectionResume: 3> if the UE is configured to provide the measurement gap requirement information of NR target bands: 4> if the RRCReconfiguration message includes the needForGapsConfigNR; or 4> if the NeedForGapsInfoNR information is changed compared to last time the UE reported this information: 5> include the NeedForGapsInfoNR and set the contents as follows: 6> include intraFreq-needForGap and set the gap requirement information of intra-frequency measurement for each NR serving cell; 6> if requestedTargetBandFilterNR is configured: 7> for each supported NR band that is also included in requestedTargetBandFilterNR, include an entry in interFreq-needForGap and set the gap requirement information forthat band; 6> else: 7> include an entry in interFreq-needForGap and set the corresponding gap requirement information for each supported NR band; 3> if the UE is configured to provide the measurement gap and NCSG requirement information of NR target bands: 4> if the RRCReconfiguration message includes the needForGapNCSG-ConfigNR; or 4> if the needForGapNCSG-InfoNR information is changed compared to last time the UE reported this information: 5> include the NeedForGapNCSG-InfoNR and set the contents as follows: 6> include intraFreq-needForNCSG and set the gap and NCSG requirement information of intra-frequency measurement for each NR serving cell; 6> if requestedTargetBandFilterNCSG-NR is configured: 7> for each supported NR band included in requestedTargetBandFilterNCSG-NR, include an entry in interFreq-needForNCSG and set the NCSG requirement information forthat band; 6> else: 7> include an entry for each supported NR band in interFreq-needForNCSG and set the corresponding NCSG requirement information; 3> if the UE is configured to provide the measurement gap and NCSG requirement information of E UTRA target bands: 4> if the RRCReconfiguration message includes the needForGapNCSG-ConfigEUTRA; or 4> if the needForGapNCSG-InfoEUTRA information is changed compared to last time the UE reported this information: 5> include the NeedForGapNCSG-InfoEUTRA and set the contents as follows: 6> if requestedTargetBandFilterNCSG-EUTRA is configured, for each supported E-UTRA band included in requestedTargetBandFilterNCSG-EUTRA, include an entry in needForNCSG-EUTRA and set the NCSG requirement information for that band; otherwise, include an entry for each supported E-UTRA band in needForNCSG-EUTRA and set the corresponding NCSG requirement information; 2> if this procedure is initiated due to the generation of a complete LTM candidate cell configuration: 3> the procedure ends. Option 3. Upon the reception of RRCReconfiguation, RRCReconfiguationComplete is generated corresponding to the RRCReconfiguration, and sent to the source cell (serving cell or the current cell UE received the RRCReconfiguration from). A RRCReconfigurationComplete message is generated and sent to the target LTM cell if the Random Access procedure is triggred upon the reception of LTM triggering MAC CE (or LTM cell switch execution) (e.g. by Message 3). However, the RRCReconfigurationComplete message is not generated and not sent to the target LTM Cell if the random access procedure is not triggered or not performed (i.e. skipped (RACH-less case) upon the reception of LTM triggering MAC CE (or LTM cell switch execution). UE can perform the uplink data transmission without RRCReconfigurationComplete messge (i.e. only with user plane data). This Option 3 reduces the signalling overhead on top of the benefits of Option2. NOTE : To reduce the processing delay for generation of RRCReconfiguration complete, UE may generate the RRCReconfigurationComplete message for each LTM candidate cell configuration upon the reception of RRCReconfiguration message including the Itm-CandidateConfig (LTM candidate cell configuration) in advance, i.e. UE can decide to send one of RRCReconfiguationComplete messages based on the received LTM triggering MAC CE in MAC entity for LTM cell switch procedure. 3> if the LTM cell switch is triggered from lower layers (e.g. by receiving the LTM triggering MAC CE in MAC entity or LTM cell switch execution) or if the target LTM candidate cell configuration is applied due to a LTM candidate cell execution or the Random Access procedure is triggered (or if lower layers (i.e. MAC layer) indicate that a Random Access procedure is needed for LTM Cell execution or if BFI_COUNTER >= beamFailurelnstanceMaxCount for the target LTM candidate cell or the timeAlignmentTimer associated with the target LTM candidate cell (or TAG that the target LTM cell belongs to) is not running or if the first MAC CE does not include TA value (i.e. Timing Advance Command) or if the first MAC CE indicates that a Random access procedure is needed by indicator (e.g. special TA value)) (In another embodiment, the second RRCReconfigurationComplete message can be generated when the LTM cell switch (LTM execution) is successfully completed.): 2> set the content of the RRCReconfigurationComplete message as follows: 3> include the LTM candidate cell configuration / information (e.g. cell identity or UE identity or configuration index or configuration identity) for the target cell indicated from lower layers (e.g. as indicated by LTM triggering MAC CE) NOTE : In case this procedure is initiated due to the generation of a complete LTM candidate cell configuration, the UE should generate only one RRCReconfigurationComplete message even if it process the LTM reference configuration and a LTM candidate cell configuration. The RRCReconfigurationComplete message includes the contents for the target cell indicated by LTM triggering MAC CE. 1> if the RRCReconfiguration message includes the Itm-CandidateConfig (LTM candidate cell configuration): 2> perform the LTM configuration procedure as specified in 3.3.1.3; 4> set the content of the RRCReconfigurationComplete message as follows: NOTE : In case this procedure is initiated due to the generation of a complete LTM candidate cell configuration, the UE should generate only one RRCReconfigurationComplete message even if it process the LTM reference configuration and a LTM candidate cell configuration. The RRCReconfigurationComplete message includes the contents for the target cell indicated by LTM triggering MAC CE. 2> if the RRCReconfiguration includes the masterCellGroup containing the reportUplinkTxDirectCurrent: 3> include the uplinkTxDirectCurrentList for each MCG serving cell with UL; 3> include uplinkDirectCurrentBWP-SUL for each MCG serving cell configured with SUL carrier, if any, within the uplinkTxDirectCurrentList; 2> if the RRCReconfiguration includes the masterCellGroup containing the reportUplinkTxDirectCurrentTwoCarrier: 3> include in the uplinkTxDirectCurrentTwoCarrierList the list of uplink Tx DC locations for the configured intra-band uplink carrier aggregation in the MCG; 2> if the RRCReconfiguration includes the masterCellGroup containing the reportUplinkTxDirectCurrentMoreCarrier: 3> include in the uplinkTxDirectCurrentMoreCarrierList the list of uplink Tx DC locations for the configured intra-band uplink carrier aggregation in the MCG; 2> if the RRCReconfiguration includes the secondaryCellGroup containing the reportUplinkTxDirectCurrent: 3> include the uplinkTxDirectCurrentList for each SCG serving cell with UL; 3> include uplinkDirectCurrentBWP-SUL for each SCG serving cell configured with SUL carrier, if any, within the uplinkTxDirectCurrentList; 2> if the RRCReconfiguration includes the secondaryCellGroup containing the reportUplinkTxDirectCurrentTwoCarrier: 3> include in the uplinkTxDirectCurrentTwoCarrierList the list of uplink Tx DC locations for the configured intra-band uplink carrier aggregation in the SCG; 2> if the RRCReconfiguration includes the secondaryCellGroup containing the reportUplinkTxDirectCurrentMoreCarrier: 3> include in the uplinkTxDirectCurrentMoreCarrierList the list of uplink Tx DC locations for the configured intra-band uplink carrier aggregation in the SCG; NOTE Ob: The UE does not expect that the reportUplinkTxDirectCurrentTwoCarrier or reportUplinkTxDirectCurrentMoreCarrier is received in both masterCellGroup and in secondaryCellGroup. Network only configures at most one of reportUplinkTxDirectCurrent, reportUplinkTxDirectCurrentTwoCarrier or reportUplinkTxDirectCurrentMoreCarrier in one RRC message. 2> if the RRCReconfiguration message includes the mrdc-SecondaryCellGroupConfig with mrdc-SecondaryCellGroup set to eutra-SCG: 3> include in the eutra-SCG-Response the E-UTRA RRCConnectionReconfigurationComplete message in accordance with TS 36.331clause 5.3.5.3; 2> if the RRCReconfiguration message includes the mrdc-SecondaryCellGroupConfig with mrdc-SecondaryCellGroup set to nr-SCG: 3> include in the nr-SCG-Response the SCG RRCReconfigurationComplete message; 3> if the RRCReconfiguration message is applied due to conditional reconfiguration execution and the RRCReconfiguration message does not include the reconfigurationWithSync in the masterCellGroup: 4> include in the selectedCondRRCReconfig the condReconfigld for the selected cell of conditional reconfiguration execution; 2> if the RRCReconfiguration includes the reconfigurationWithSync in spCellConfig of an MCG: 3> if the UE has logged measurements available for NR and if the RPLMN is included in plmn-ldentityList stored in VarLogMeasReport: 4> include the logMeasAvailable in the RRCReconfigurationComplete message; 4> if Bluetooth measurement results are included in the logged measurements the UE has available for NR: 5> include the logMeasAvailableBT in the RRCReconfigurationComplete message; 4> if WLAN measurement results are included in the logged measurements the UE has available for NR: 5> include the logMeasAvailableWLAN in the RRCReconfigurationComplete message; 3> if the sigLoggedMeasType in VarLogMeasReport is included: 4> if T330 timer is running and the logged measurements configuration is for NR: 5> set sigLogMeasConfigAvailable to true in the RRCReconfigurationComplete message; 4> else: 5> if the UE has logged measurements available for NR: 6> set sigLogMeasConfigAvailable to false in the RRCReconfigurationComplete message; 3> if the UE has connection establishment failure or connection resume failure information available in VarConnEstFailReport or VarConnEstFailReportList and if the RPLMN is equal to plmn-ldentity stored in VarConnEstFailReport or in at least one of the entries of VarConnEstFailReportList: 4> include connEstFaillnfoAvailable in the RRCReconfigurationComplete message; 3> if the UE has radio link failure or handover failure information available in VarRLF-Report and if the RPLMN is included in plmn-ldentityList stored in VarRLF-Report; or 3> if the UE has radio link failure or handover failure information available in VarRLF-Report of TS 36.331

[10] and if the UE is capable of cross-RAT RLF reporting and if the RPLMN is included in plmn-ldentityList stored in VarRLF-Report of TS 36.331

[10] : 4> include rlf-InfoAvailable in the RRCReconfigurationComplete message; 3> if the UE was configured with successHO-Config when connected to the source Pcell; and 3> if the applied RRCReconfiguration is not due to a conditional reconfiguration execution upon cell selection performed while timer T311 was running, as defined in 5.3.7.3: 4> perform the actions for the successful handover report determination as specified in clause 5.7.10.6, upon successfully completing the Random Access procedure triggered for the reconfigurationWithSync in spCellConfig of the MCG; 3> if the UE has successful handover information available in VarSuccessHO-Report and if the RPLMN is included in plmn-ldentityList stored in VarSuccessHO-Report: 4> include successHO-InfoAvailable in the RRCReconfigurationComplete message; 2> if the RRCReconfiguration message was received via SRB1, but not within mrdc-SecondaryCellGroup or E-UTRA RRCConnectionReconfiguration or E-UTRA RRCConnectionResume: 3> if the UE is configured to provide the measurement gap requirement information of NR target bands: 4> if the RRCReconfiguration message includes the needForGapsConfigNR; or 4> if the NeedForGapsInfoNR information is changed compared to last time the UE reported this information: 5> include the NeedForGapsInfoNR and set the contents as follows: 6> include intraFreq-needForGap and set the gap requirement information of intra-frequency measurement for each NR serving cell; 6> if requestedTargetBandFilterNR is configured: 7> for each supported NR band that is also included in requestedTargetBandFilterNR, include an entry in interFreq-needForGap and set the gap requirement information forthat band; 6> else: 7> include an entry in interFreq-needForGap and set the corresponding gap requirement information for each supported NR band; 3> if the UE is configured to provide the measurement gap and NCSG requirement information of NR target bands: 4> if the RRCReconfiguration message includes the needForGapNCSG-ConfigNR; or 4> if the needForGapNCSG-InfoNR information is changed compared to last time the UE reported this information: 5> include the NeedForGapNCSG-InfoNR and set the contents as follows: 6> include intraFreq-needForNCSG and set the gap and NCSG requirement information of intra-frequency measurement for each NR serving cell; 6> if requestedTargetBandFilterNCSG-NR is configured: 7> for each supported NR band included in requestedTargetBandFilterNCSG-NR, include an entry in interFreq-needForNCSG and set the NCSG requirement information forthat band; 6> else: 7> include an entry for each supported NR band in interFreq-needForNCSG and set the corresponding NCSG requirement information; 3> if the UE is configured to provide the measurement gap and NCSG requirement information of E UTRA target bands: 4> if the RRCReconfiguration message includes the needForGapNCSG-ConfigEUTRA; or 4> if the needForGapNCSG-InfoEUTRA information is changed compared to last time the UE reported this information: 5> include the NeedForGapNCSG-InfoEUTRA and set the contents as follows: 6> if requestedTargetBandFilterNCSG-EUTRA is configured, for each supported E-UTRA band included in requestedTargetBandFilterNCSG-EUTRA, include an entry in needForNCSG-EUTRA and set the NCSG requirement information for that band; otherwise, include an entry for each supported E-UTRA band in needForNCSG-EUTRA and set the corresponding NCSG requirement information; 2> if this procedure is initiated due to the generation of a complete LTM candidate cell configuration: 3> the procedure ends. As set out above, RRCReconfigurationComplete message is generated and transmitted to the target LTM candidate cell during LTM execution procedure or when the target LTM cell configuration (indicated by the configuration Identify in the first MAC CE) is applied or upon the reception of the first MAC CE in Option 1, Option 2 or Option 3 (e.g. if the Random Access procedure (or RACH-less solution) is triggered upon the reception of LTM triggering MAC CE). Option 1, Option 2 or Option 3, set out how to submit the RRCReconfigurationComplete message via which SRB during LTM execution procedure, which is also extended to the dual connectivity scenario (e.g. for UE configured with MCG and SCG). As set out herein, the LTM candidate cell configurations can be configured via SRB1 or split SRB1 or SRB3 by RRCReconfiguration message. The LTM candidate cell configurations for MCG or SCG can be configured via SRB1 or split SRB1 or SRB3 by RRCReconfiguration message. The RRCReconfiguraton message including LTM candidate cell configurations does not include reconfigurationWithSync to avoid RRC message triggered handover. In another embodiment, RRCReconfiguraton message including LTM candidate cell configurations includes reconfigurationWithSync but it should not trigger a Random access procedure. For MCG case, the generation of RRCReconfiguration can automatically trigger a Random access procedure over cell change. With this reason, especially, for the SCG case (i.e. if the RRCReconfiguration message was received via SRB1 within the nr-SCG within mrdc-SecondaryCellGroup (UE in NR-DC, mrdc-SecondaryCellGroup was received in RRCReconfiguration or RRCResume via SRB1), do not initiate the Random Access procedure on the PSCell if reconfigurationWithSync was included in spCellConfig in NR SCG and if the RRCReconfiguration message is applied due to an LTM cell switch execution. For example, if the scg-State is not included in the RRCReconfiguration or RRCResume message containing the RRCReconfiguration message and if reconfigurationWithSync was included in spCellConfig in nr-SCG and if the RRCReconfiguration message is not applied due to an LTM cell switch execution, UE initiates the Random Access procedure on the PSCell. In another example, if the scg-State is not included in the RRCReconfiguration or RRCResume message containing the RRCReconfiguration message and if reconfigurationWithSync was included in spCellConfig in nr-SCG and if the RRCReconfiguration message is not applied due to an LTM cell switch execution for which a lower layer indicates to skip the Random Access procedure, UE initiates the Random Access procedure on the PSCell. The UE configured with single connectivity (i.e. MCG only) or not configured with dual connectivity (i.e. MCG and SCG or MCG) can be configured with LTM candidate cell configurations (e.g. for MCG) by the reception of a first RRCReconfiguration message via SRB1. Then, a first RRCReconfigurationComplete message corresponding to the first RRCReconfiguration can be generated and sent to the source serving cell (Master gNB, i.e. MCG) via SRB1 where sent the first RRCReconfiguration message to UE. When UE receives the first MAC CE including the target LTM configuration ID (Identity) from the source serving cell, UE can apply the corresponding target LTM configuration (e.g for MCG) (or RRCReconfiguration for the target LTM cell of MCG) indicated by the configuration ID in the first MAC CE. Upon the reception of the first MAC CE or the application of the target LTM configuration, UE generates a second RRCReconfigurationComplete corresponding the target LTM configuration with the contents (e.g. configuration ID or information for the target LTM configuration or reply or confirmation) and sends to the target cell (or gNB or MCG) via SRB1. In another embodiment, the second RRCReconfigurationComplete message can be generated when the LTM cell switch (LTM execution) is successfully completed. Furthermore, the first RRCReconfigurationComplete is submitted as follows (which can be also applied to UE configured with dual connectivity): 1> if the UE is configured with E-UTRA nr-SecondaryCellGroupConfig (UE in (NG)EN-DC): 2> submit the first RRCReconfigurationComplete via E-UTRA; 1> else if the first RRCReconfiguration message was received via SRB3 (UE in NR-DC): 2> if the first RRCReconfiguration message was received within DLlnformationTransferMRDC: 3> if the first RRCReconfiguration message was received within the nr-SCG within mrdc-SecondaryCellGroup (NR SCG RRC Reconfiguration): 4> perform SCG reconfiguration accordingly: 3> else (e.g. first RRCReconfiguration message was received within master cell group configuration (NR MCG RRCReconfiguration): 4> submit the first RRCReconfigurationComplete message via SRB1 to lower layers for transmission using the new configuration; 2> else: 3> submit the first RRCReconfigurationComplete message via SRB3 to lower layers for transmission using the new configuration; 1 >else (the first RRCReconfiguration was received via SRB1): 2> submit the first RRCReconfigurationComplete message via SRB1 to lower layers for transmission using the new configuration; The UE configured with dual connectivity (i.e. MCG and SCG) can be configured with LTM candidate cell configurations (e.g. for MCG or SCG) by the reception of a first RRCReconfiguration message via SRB1 (or split SRB1) or SRB3. a first RRCReconfigurationComplete message corresponding to the first RRCReconfiguration can be generated and sent to the source serving cell. For each case of dual connectivity, howto submit the second RRCReconfigurationComplete is as follows. If a UE is configured with LTM candidate cell configuration for SCG or if the LTM cell switch is triggered from lower layers (e.g. by receiving the LTM triggering MAC CE from SCG in MAC entity of SCG or LTM cell switch execution in SCG) or if the target LTM candidate cell configuration for SCG is applied due to a LTM candidate cell execution, UE generates the second RRCReconfigurationComplete message. And then, if the UE is configured with E-UTRA nr-SecondaryCellGroupConfig (UE in (NG)EN-DC), UE submit the second RRCReconfigurationComplete via E-UTRA. In another embodiment, the second RRCReconfigurationComplete message can be generated when the LTM cell switch (LTM execution) is successfully completed. If a UE is configured with LTM candidate cell configuration for SCG or if the LTM cell switch is triggered from lower layers (e.g. by receiving the LTM triggering MAC CE from SCG in MAC entity of SCG or LTM cell switch execution in SCG) or if the target LTM candidate cell configuration for SCG is applied due to a LTM candidate cell execution, UE generates the second RRCReconfigurationComplete message. And then, if the RRCReconfiguration message (or LTM candidate configuration for SCG) was received via SRB1 within the nr-SCG within mrdc-SecondaryCellGroup (UE in NR-DC, mrdc-SecondaryCellGroup was received in RRCReconfiguration or RRCResume via SRB1), UE submits the second RRCReconfigurationComplete message (e.g. to SCG or MCG via SRB1 (or via split SRB1)) via the NR MCG embedded in NR RRC message ULInformationTransferMRDC. In another embodiment, the second RRCReconfigurationComplete message can be generated when the LTM cell switch (LTM execution) is successfully completed. If a UE is configured with received via SRB3 (UE in NR-DC) and if the RRCReconfiguration message (or LTM candidate configuration for SCG) was received within DLlnformationTransferMRDC and if the RRCReconfiguration message was not received within the nr-SCG within mrdc-SecondaryCellGroup (i.e. it’s not NR SCG RRC Reconfiguration, or if target LTM candidate cell configuration for SCG or if the LTM cell switch is triggered from lower layers (e.g. by receiving the LTM triggering MAC CE from SCG in MAC entity of SCG or LTM cell switch execution in SCG) or if the target LTM candidate cell configuration for SCG is applied due to a LTM candidate cell execution, UE generates the second RRCReconfigurationComplete message. And then, if the RRCReconfiguration message (or LTM candidate configuration for SCG) was LTM candidate configuration was received within master cell group configuration (i.e. it’s NR MCG RRCReconfiguration), UE submits the second RRCReconfigurationComplete message via SRB1 to lower layers for transmission using the new configuration because DLlnformationTransferMRDC includes the configuration from MCG, which need to be sent to MCG via SRB1. In another embodiment, the second RRCReconfigurationComplete message can be generated when the LTM cell switch (LTM execution) is successfully completed. If a UE is configured with LTM candidate cell configuration for SCG or if the LTM cell switch is triggered from lower layers (e.g. by receiving the LTM triggering MAC CE from SCG in MAC entity of SCG or LTM cell switch execution in SCG) or if the target LTM candidate cell configuration for SCG is applied due to a LTM candidate cell execution, UE generates the second RRCReconfigurationComplete message. And then, if the RRCReconfiguration message (or LTM candidate configuration for SCG) was received via SRB3 (UE in NR-DC) and if the RRCReconfiguration message (or LTM candidate configuration for SCG) was not received within DLlnformationTransferMRDC, UE submits the second RRCReconfigurationComplete message via SRB3 to lower layers for transmission using the new configuration because the configuration corresponds to SCG, which need to be sent to SCG via SRB3. In another embodiment, the second RRCReconfigurationComplete message can be generated when the LTM cell switch (LTM execution) is successfully completed. If a UE is configured with LTM candidate cell configuration for SCG or if the LTM cell switch is triggered from lower layers (e.g. by receiving the LTM triggering MAC CE from SCG in MAC entity of SCG or LTM cell switch execution in SCG) or if the target LTM candidate cell configuration for SCG is applied due to a LTM candidate cell execution, UE generates the second RRCReconfigurationComplete message. And then, if RRCReconfiguration (or LTM candidate configuration for SCG) was received via SRB1, UE submits the RRCReconfigurationComplete message via SRB1 to lower layers for transmission using the new configuration. In another embodiment, the second RRCReconfigurationComplete message can be generated when the LTM cell switch (LTM execution) is successfully completed. To implement the details described above, specifically, the UE shall perform the following actions upon reception of the RRCReconfiguration, or upon execution of the conditional reconfiguration (CHO, CPA or CPC) or upon execution of LTM procedure (or LTM cell switch): 1> if the LTM cell switch is triggered from lower layers (e.g. by receiving the LTM triggering MAC CE in MAC entity or LTM cell switch execution) or if the target LTM candidate cell configuration is applied due to a LTM candidate cell execution: 2> set the content of the second RRCReconfigurationComplete message as follows: 3> include the LTM candidate cell configuration / information (e.g. cell identity or UE identity or configuration index or configuration identity) for the target cell indicated from lower layers (e.g. as indicated by LTM triggering MAC CE) 3> if the RRCReconfiguration message includes the mrdc-SecondaryCellGroupConfig with mrdc-SecondaryCellGroup set to nr-SCG: 4> include in the nr-SCG-Response the SCG RRCReconfigurationComplete message; 4> if the RRCReconfiguration message is applied due to conditional reconfiguration execution and the RRCReconfiguration message does not include the reconfigurationWithSync in the masterCellGroup: 5> include in the selectedCondRRCReconfig the condReconfigld for the selected cell of conditional reconfiguration execution; 4> if the RRCReconfiguration (or target LTM candidate configuration) is applied due to a LTM candidate cell execution for LTM cell switch (e.g. triggered by the reception of the first MAC CE) which can be configured via LTM candidate cell configuration contained in nr-SCG within mrdc-SecondaryCellGroup: 5> include in the selected LTM candidate configuration the configuration ID (Identity) for the selected LTM candidate cell of LTM execution. The configuration ID can be indicated by the first MAC CE; T o ease the network implementation for handling of the second RRCReconfigurationComplete messages, the second RRCReconfigurationComplete is submitted as follows: 1> if the UE is configured with E-UTRA nr-SecondaryCellGroupConfig (UE in (NG)EN-DC): 2> submit the second RRCReconfigurationComplete via E-UTRA; 1> else if the RRCReconfiguration message (or target LTM candidate configuration) was received via SRB1 within the nr-SCG within mrdc-SecondaryCellGroup (UE in NR-DC, mrdc-SecondaryCellGroup was received in RRCReconfiguration or RRCResume via SRB1): 2> if the RRCReconfiguration is applied due to a conditional reconfiguration execution for CPC which is configured via conditionalReconfiguration contained in nr-SCG within mrdc-SecondaryCellGroup; or 2> if the RRCReconfiguration (or target LTM candidate configuration) is applied due to a LTM candidate cell execution for LTM cell switch (e.g. triggered by the reception of the first MAC CE) which can be configured via LTM candidate cell configuration contained in nr-SCG within mrdc-SecondaryCellGroup: 3> submit the second RRCReconfigurationComplete message (e.g. to SCG or MCG via SRB1 (or via split SRB1)) via the NR MCG embedded in NR RRC message ULInformationTransferMRDC, e.g. The UE shall set the contents of the ULInformationTransferMRDC message as follows: if there is a need to transfer MR-DC dedicated information related to NR, UE sets the ul-DCCH-MessageNR to include the NR MR-DC dedicated information to be transferred (e.g., NR RRC MeasurementReport, UEAssistancelnformation, Failureinformation, RRCReconfigurationComplete, MCGFailurelnformation, or lABOtherlnformation message. 1> else if the RRCReconfiguration message (or target LTM candidate configuration) was received via SRB3 (UE in NR-DC): 2> if the RRCReconfiguration message (or target LTM candidate configuration) was received within DLlnformationTransferMRDC: 3> if the RRCReconfiguration message was received within the nr-SCG within mrdc-SecondaryCellGroup (NR SCG RRC Reconfiguration): 4> perform SCG reconfiguration accordingly: 3> else (e.g. target LTM candidate configuration was received within master cell group configuration (NR MCG RRCReconfiguration): 4> submit the second RRCReconfigurationComplete message via SRB1 to lower layers for transmission using the new configuration; 2> else: 3> submit the second RRCReconfigurationComplete message via SRB3 to lower layers for transmission using the new configuration; 1> else (RRCReconfiguration (or target LTM candidate configuration) was received via SRB1): 2> submit the second RRCReconfigurationComplete message via SRB1 to lower layers for transmission using the new configuration; The DLlnformationTransferMRDC message is used for the downlink transfer of RRC messages during fast MCG link recovery via SRB3 while the ULInformationTransferMRDC message is used for the uplink transfer of MR-DC dedicated information via SRB1 or SRB3 (e.g. for transferring the NR or E-UTRA RRC MeasurementReport message, the Failureinformation message, the UEAssistancelnformation message, the RRCReconfigurationComplete message, the lABOtherlnformation message or the NR or E-UTRA RRC MCGFailurelnformation message). In another embodiment, the UE configured with dual connectivity (i.e. MCG and SCG) can be configured with LTM candidate cell configurations (e.g. for MCG or SCG) by the reception of a first RRCReconfiguration message via SRB1 (or split SRB1) or SRB3. a first RRCReconfigurationComplete message corresponding to the first RRCReconfiguration can be generated and sent to the source serving cell. For each case of dual connectivity, howto submit the second RRCReconfigurationComplete is as follows. If a UE is configured with LTM candidate cell configuration for MCG or if the LTM cell switch is triggered from lower layers (e.g. by receiving the LTM triggering MAC CE from MCG in MAC entity of MCG or LTM cell switch execution in MCG) or if the target LTM candidate cell configuration for MCG is applied due to a LTM candidate cell execution, UE generates the second RRCReconfigurationComplete message. And then, if RRCReconfiguration (or LTM candidate configuration for MCG) was received via SRB1, UE submits the RRCReconfigurationComplete message via SRB1 to lower layers for transmission using the new configuration. In another embodiment, the second RRCReconfigurationComplete message can be generated when the LTM cell switch (LTM execution) is successfully completed. If a UE is configured with LTM candidate cell configuration for SCG or if the LTM cell switch is triggered from lower layers (e.g. by receiving the LTM triggering MAC CE from SCG in MAC entity of SCG or LTM cell switch execution in SCG) or if the target LTM candidate cell configuration for SCG is applied due to a LTM candidate cell execution, UE generates the second RRCReconfigurationComplete message. And then, if the RRCReconfiguration message (or LTM candidate configuration for SCG) was received via SRB1 within the nr-SCG within mrdc-SecondaryCellGroup (UE in NR-DC, mrdc-SecondaryCellGroup was received in RRCReconfiguration or RRCResume via SRB1), UE submits the second RRCReconfigurationComplete message (e.g. to SCG or MCG via SRB1 (or via split SRB1)) via the NR MCG embedded in NR RRC message ULInformationTransferMRDC. In another embodiment, the second RRCReconfigurationComplete message can be generated when the LTM cell switch (LTM execution) is successfully completed. If a UE is configured with LTM candidate cell configuration for SCG or if the LTM cell switch is triggered from lower layers (e.g. by receiving the LTM triggering MAC CE from SCG in MAC entity of SCG or LTM cell switch execution in SCG) or if the target LTM candidate cell configuration for SCG is applied due to a LTM candidate cell execution, UE generates the second RRCReconfigurationComplete message. And then, if the RRCReconfiguration message (or LTM candidate configuration for SCG) was received via SRB3 (UE in NR-DC) and if the RRCReconfiguration message (or LTM candidate configuration for SCG) was not received within DLlnformationTransferMRDC, UE submits the second RRCReconfigurationComplete message via SRB3 to lower layers for transmission using the new configuration because the configuration corresponds to SCG, which need to be sent to SCG via SRB3 and the DLlnformationTransferMRDC message is used for the downlink transfer of RRC messages during fast MCG link recovery. In another embodiment, the second RRCReconfigurationComplete message can be generated when the LTM cell switch (LTM execution) is successfully completed. If a UE is configured with LTM candidate cell configuration for SCG or if the LTM cell switch is triggered from lower layers (e.g. by receiving the LTM triggering MAC CE from SCG in MAC entity of SCG or LTM cell switch execution in SCG) or if the target LTM candidate cell configuration for SCG is applied due to a LTM candidate cell execution, UE generates the second RRCReconfigurationComplete message. And then, if RRCReconfiguration (or LTM candidate configuration for SCG) was received via SRB1, UE submits the RRCReconfigurationComplete message via SRB1 to lower layers for transmission using the new configuration. In another embodiment, the second RRCReconfigurationComplete message can be generated when the LTM cell switch (LTM execution) is successfully completed. In another embodiment, the UE configured with dual connectivity (i.e. MCG and SCG) can be configured with LTM candidate cell configurations (e.g. for MCG or SCG) by the reception of a first RRCReconfiguration message via SRB1 (or split SRB1) or SRB3. a first RRCReconfigurationComplete message corresponding to the first RRCReconfiguration can be generated and sent to the source serving cell. For each case of dual connectivity, howto submit the second RRCReconfigurationComplete is as follows. If a UE is configured with LTM candidate cell configuration for MCG (or SCG) or if the LTM cell switch is triggered from lower layers (e.g. by receiving the LTM triggering MAC CE from MCG (or SCG) in MAC entity of MCG (or SCG) or LTM cell switch execution in MCG(or SCG)) or if the target LTM candidate cell configuration for MCG (or SCG) is applied due to a LTM candidate cell execution, UE generates the second RRCReconfigurationComplete message. And then, UE submits the second RRCReconfigurationComplete as follows: (In another embodiment, the second RRCReconfigurationComplete message can be generated when the LTM cell switch (LTM execution) is successfully completed). 1> if the UE is in (NG)EN-DC: 2> if SRB3 is configured or the SCG is not deactivated: 3> submit the second RRCReconfigurationComplete via SRB3 to lower layers for transmission, upon which the procedure ends; 2> else: 3> submit the second RRCReconfigurationComplete via E-UTRA embedded in E-UTRA RRC message ULInformationTransferMRDC. 1> else if the UE is in NR-DC: 2> if the LTM candidate cell configuration is associated with the SCG: 3> if SRB3 is configured or the SCG is not deactivated: 4> submit the second RRCReconfigurationComplete via SRB3 to lower layers for transmission, upon which the procedure ends; 3> else: 4> submit the second RRCReconfigurationComplete via SRB1 embedded in NR RRC message ULInformationTransferMRDC', 2> else: 3> submit the second RRCReconfigurationComplete via SRB1 to lower layers for transmission, upon which the procedure ends; 1> else (i.e. UE configured with single connectivity): 2> submit the second RRCReconfigurationComplete to lower layers for transmission, upon which the procedure ends. In embodiments of this invention, LTM execution procedure for SCG can be performed if (or when) the SCG is not deactivated or if (or when) the SCG is activated. In embodiments of this invention, the LTM configuration for candidate cells can indicate the reference configuration for LTM candidate cells or the complete configuration for LTM candidate cells. The reference configuration can be the complete configuration or the reference configuration and a LTM candidate-cell specific configuration can be the complete configuration for the LTM candidate cell. Upon LTM execution, UE can suspend all radio bearers except SRBs (e.g. SRBO, SRB1, SRB2, SRB3, SRB4 or SRB5), in order to avoid the data processing or data transmission (or reception) to the source cell or to avoid the data transmission in the random access procedure to the target cell. After the successful completion of LTM execution (or LTM cell switch to the target cell), UE can resume all suspended radio bearers except the SRBs to start the data transmission or reception. The UE shall perform the following actions based on a received LTM-CandidateConfig IE: 1> store the received Itm-ReferenceConfiguration in VarLTM-Config, if present; 1 >if the LTM-CandidateConfig includes the Itm-CandidateToReleaseList: 2> perform the LTM candidate cell release; 1 >if the LTM-CandidateConfig includes the Itm-CandidateToAddModList: 2> perform the LTM candidate cell addition or reconfiguration; 1> perform the actions to generate a complete LTM configuration; NOTE X: It is up to the UE implementation to postpone the generation of a complete LTM configuration until the executing of an LTM cell switch. The following relates to LTM candidate cell release. The UE shall: 1 >for each Itm-Candidateld in the Itm-CandidateToReleaseList: 2> if the current VarLTM-Config includes an Itm-Candidate with the given Itm-Candidateld: 3> release the Itm-Candidate from VarLTM-Config; The LTM candidate cell configuration can be automatically released by UE in the following cases (or it can be released by the explicit indicator of the received RRC messages): - Upon the successful completion of LTM execution (or LTM cell switch) - Upon the reception of RRCRelease message (because LTM execution is available only in RRC CONNECTED state) - if the RRCSetup is received in response to an RRCReestablishmentRequest (because this means that UE failed to RRC Reestablishment procedure when UE sent an RRCReestablishmentRequest to recover the RRC connection with the network), where The RRCSetup message is used to establish SRB1 and transmitted (or received) via SRBO. In another embodiment, UE can release the LTM candidate cell configuration upon the reception of RRCRelease message indicating the transition to RRC IDLE mode while UE can store or keep it upon reception of RRCRelease message indicating the transition to RRC INACTIVE mode and it can be re-configured or used to resume RRC connection with RRCResume message. For example, RRCRelease message indicating the state transition to RRC INACTIVE can also indicate UE whether to keep or release the LTM candidate cell configuration. When UE performs RRC Resume procedure, the network can send RRCResume message including a indicator whether to whether to restore or release the LTM candidate cell configuration. The following relates to LTM candidate cell addition / modification. The UE shall: 1 >for each Itm-Candidateld in the Itm-CandidateToAddModList: 2> if the current VarLTM-Config includes an Itm-Candidate with the given Itm-Candidateld'. 3> modify the Itm-Candidate within VarLTM-Config in accordance with the received Itm-Candidate; 2> else: 3> add the received Itm-Candidate to VarLTM-Config. The following relates to Generation of UE LTM configuration.The purpose of this procedure is for the UE to generate a complete LTM candidate cell configuration (or LTM candidate cell configuration) for each LTM candidate cell to be stored and the LTM candidate cell configuration for the target cell indicated by lower layers (i.e. as indicated by LTM triggering MAC CE) is applied only when an indication of an LTM cell switch is received by lower layers. During the generation of a complete LTM candidate cell configuration, the current UE configuration shall not be modified. The UE shall: 1> for each Itm-Candidate in Itm-CandidateConfigList within VarLTM-Config; 2> store the Itm-Candidateld included in Itm-Candidate within VarLTM-UE-Config; 2> it Itm-Candidate includes Itm-ConfigComplete; 3> generate a complete LTM candidate cell configuration for the received Itm-Candidate according to the actions and store it in ue-LTM-Config within VarLTM-UE-Config. 2> else: 3> generate a complete LTM candidate cell configuration by applying Itm-Candidate on top of referenceconfiguration according to the actions and store it in ue-LTM-Config within VarLTM-UE-Config. The following relates to LTM cell switch execution. Upon the indication by lower layers that an LTM cell switch procedure is triggered, the UE shall: 1> release / clear all current dedicated radio configuration except for the following: 2> if the LTM cell switch is triggered on the MCG: the MCG C-RNTI; UE needs to maintain or keep the MCG C-RNTI upon the indication by lower layers that an LTM cell switch procedure is triggered on the MCG as UE may use this RNTI at RLF or at RRC Re-establishent procedure, which can occur during LTM scell switch procedure. the AS security configurations associated with the master key; 2> else, if the LTM cell switch is triggered on the SCG: UE doesn’t have to keep the SCG C-RNTI as there is no use case for this RNTI during LTM scell switch procedure, (i.e. UE discards (or releases or clears) SCG C-RNTI upon the indication by lower layers that an LTM cell switch procedure is triggered on the SCG)- the AS security configurations associated with the secondary key; the SRB1 / SRB2 configurations and DRB configurations as configured by radioBearerConfig or radioBearerConfig2' the UE variables VarLTM-Config and VarLTM-UE-Config. 1> release / clear all current common radio configuration associated with the cell group for which the LTM cell switch procedure is triggered; 1> use the default values specified for timers T310, T311 and constants N310, N311 associated with the cell group for which the LTM cell switch procedure is triggered; 1> apply the default L1 parameter values as specified in corresponding physical layer specifications except for the following: parameters for which values are provided in SIB1 (i.e. system information); 1 >apply the value of the newUE-ldentity as the C-RNTI for this cell group according to the LTM candidate cell configuration related to the the LTM candidate cell configuration identity as received by lower layers; 1> configure lower layers in accordance with the received spCellConfigCommon according to the LTM candidate cell configuration indicated by lower layers; 1> configure lower layers in accordance with the received rach-ConfigDedicated according to the LTM candidate cell configuration indicated by lower layers. 1> configure the PDCP entity for LTM candidate cell configuration indicated by lower layers with state variables continuation for SRBs, and with the same security configuration as the PDCP entity for the source cell group; 1 >stop timer T310 for the corresponding SpCell, if running; 1> if this procedure is executed for the MCG: 2> if timer T316 is running; 3> stop timer T316; 1 >stop timer T312 for the corresponding SpCell, if running; 1> start timer a supervisor timer (i.e. T3xx) for this cell group with the timer value set to the configured value in RRCReconfiguration, as included within the field Itm-Timers; 1> reset the MAC entity of this cell group; 1> apply the specified BCCH configuration for the target LTM candidate cell configuration; 1> acquire the MIB of the target SpCell as indicated in the LTM candidate cell configuration indicated by lower layers, if applicable; 1> apply the LTM configuration in UE-LTM-Config within VarLTM-UE-Config related to the LTM candidate cell configuration identity as received by lower layers. 1> if the value of field Itm-NoResetID contained within the LTM-Candidate IE related to the LTM candidate cell configuration identity (Target configuration ID) as received by lower layers (i.e. MAC layer) is equal to the value of Itm-ServingCellNoResetID within VarLTM-ServingCellNoResetlD: 2> continue using the current RLC entity in the LTM candidate cell configuration indicated by lower layers; 2> replace the value of Itm-ServingCellNoResetID in VarLTM-ServingCellNoResetID with the value received within Itm-NoResetID; 1> else: 2> for each RLC-BearerConfig within rlc-BearerToAddModList that is part of current UE configuration: 3> re-establish the RLC entity; 2> for each drb-ldentity value included in the drb-ToAddModList that is part of the current UE configuration: 3> trigger the PDCP entity of this DRB to perform data recovery; 2> replace the value of Itm-ServingCellNoResetID in VarLTM-ServingCellNoResetID with the value received within Itm-NoResetID; 1> continue using the current PDCP entity in the LTM candidate cell configuration(Target configuration ID) indicated by lower layers (i.e. MAC layer);1 >apply the LTM configuration in ue-LTM-Config within VarLTM-UE-Config related to the LTM candidate cell configuration identity as received from lower layers; 1> consider the LTM candidate cell indicated by lower layers to be the serving cell; 1> if the RRCReconfiguration message including the LTM-Candidate IE related to the LTM candidate cell configuration identity (Target configuration ID) as received by lower layers (i.e. MAC layer) was received via SRB1 within the nr-SCG within mrdc-SecondaryCellGroup (UE in NR-DC): 2> submit the RRCReconfigurationComplete message via the NR MCG embedded in NR RRC message ULInformationTransferMRDC; 1> else if RRCReconfiguration message including the LTM-Candidate IE related to the LTM candidate cell configuration identity as received by lower layers was received via SRB3 (UE in NR-DC): 2> submit the RRCReconfigurationComplete message via SRB3 to lower layers for transmission using the new configuration; 1> else (RRCReconfiguration was received via SRB1): 1> 2> submit the RRCReconfigurationComplete message to lower layers for transmission via SRB1 using the new configuration.submit the RRCReconfigurationComplete message to lower layers for transmission using the new configuration. The LTM cell switch execution procedure above can be extended to cover the dual connectivity case. When UE is configured with dual connectivity (i.e. MCG and SCG). The LTM execution procedure can be initiated in either MCG or SCG. However, note that this procedure would have some impact on MCG failure recovery procedure. The MCG failure recovery is mainly managed by a timer (i.e. T316). The purpose of MCG failure recovery is to inform the network about an MCG failure the UE has experienced i.e. MCG radio link failure, which reports it to MCG via SCG (i.e. via split SRB1 or SRB3) by sending a RRC message (i.e. MCG failure information message). A UE in RRC_CONNECTED, for which AS security has been activated with SRB2 and at least one DRB or multicast MRB setup or, for IAB, SRB2, may initiate the fast MCG link recovery procedure in order to continue the RRC connection without re-establishment. A UE configured with split SRB1 or SRB3 can initiate this procedure to report MCG failures when neither MCG nor SCG transmission is suspended, the SCG is not deactivated, T316 is configured and upon detecting radio link failure of the MCG while T316 is not running. When the MCG failure is informed to MCG, the MCG can send RRC Release message, RRC Reconfiguration message with reconfigurationwithSync (i.e. handover indication) for the PCell, or MobilityFromNRCommand message via SCG (i.e. via split SRB1 or SRB3) to release or recover the RRC connection. The timer (i.e. T316) can be configured only if the UE is configured with split SRB1 or SRB3. UE starts the timer T316 when UE transmits the RRC message (i.e. MCG Failure Information message). UE submits the MCG Failure Information message to lower layers for transmission via SRB1 if SRB1 is configured as split SRB. Otherwise (i.e. SRB3 configured), UE submits the MCG Failure Information message to lower layers for transmission embedded in NR RRC message ULInformationTransferMRDC via SRB3. UE stops the timer T316 upon receiving RRC Release message, RRC Reconfiguration message with reconfigurationwithSync (i.e. handover indication) for the PCell, MobilityFromNRCommand message, or upon initiating the RRC re-establishment procedure. Upon the expiry of the timer T316, UE initiates the RRC reestablishment procedure. Considering the MCG failure recovery procedure as set out above, if T316 is running, it means that the MCG failure already happened. Therefore, it is important to carefully consider the case that LTM cell switch execution is initiated when T316 is running. To handle this case efficiently, there are the following options. One of these options can be implemented to proceed LTM execution. Option 1: In this option, if UE receives the first MAC CE and is going to initiate the LTM cell switch procedure when T316 is running, then UE can stop T316 and perform the LTM cell switch procedure as the LTM cell switch procedure can recover the MCG radio link by cell switching, which may expedite the MCG failure recovery. The corresponding procedure is as follows. Upon the indication by lower layers that an LTM cell switch procedure is triggered, the UE shall: 1> release / clear all current dedicated radio configuration except for the following: 2> if the LTM cell switch is triggered on the MCG: the MCG C-RNTI; UE needs to maintain or keep the MCG C-RNTI upon the indication by lower layers that an LTM cell switch procedure is triggered on the MCG as UE may use this RNTI at RLF or at RRC Re-establishent procedure, which can occur during LTM scell switch procedure. the AS security configurations associated with the master key; 2> else, if the LTM cell switch is triggered on the SCG: UE doesn’t have to keep the SCG C-RNTI as there is no use case for this RNTI during LTM scell switch procedure, (i.e. UE discards (or releases or clears) SCG C-RNTI upon the indication by lower layers that an LTM cell switch procedure is triggered on the SCG)-the AS security configurations associated with the secondary key; the SRB1 / SRB2 configurations and DRB configurations as configured by radioBearerConfig or radioBearerConfig2; the UE variables VarLTM-Config and VarLTM-UE-Config. 1> release / clear all current common radio configuration associated with the cell group for which the LTM cell switch procedure is triggered; 1> use the default values specified for timers T310, T311 and constants N310, N311 associated with the cell group for which the LTM cell switch procedure is triggered; 1> apply the default L1 parameter values as specified in corresponding physical layer specifications except for the following: parameters for which values are provided in SIB1 (i.e. system information); 1 >apply the value of the newUE-ldentity as the C-RNTI for this cell group according to the LTM candidate cell configuration related to the the LTM candidate cell configuration identity as received by lower layers; 1> configure lower layers in accordance with the received spCellConfigCommon according to the LTM candidate cell configuration indicated by lower layers; 1> configure lower layers in accordance with the received rach-ConfigDedicated according to the LTM candidate cell configuration indicated by lower layers. 1> configure the PDCP entity for LTM candidate cell configuration indicated by lower layers with state variables continuation for SRBs, and with the same security configuration as the PDCP entity for the source cell group; 1 >stop timer T310 for the corresponding SpCell, if running; 1> if this procedure is executed for the MCG: 2> if timer T316 is running; 3> stop timer T316; 1 >stop timer T312 for the corresponding SpCell, if running; 1> start timer a supervisor timer (i.e. T3xx) for this cell group with the timer value set to the configured value in RRCReconfiguration, as included within the field Itm-Timers; 1> reset the MAC entity of this cell group; 1> apply the specified BCCH configuration for the target LTM candidate cell configuration; 1> acquire the MIB of the target SpCell as indicated in the LTM candidate cell configuration indicated by lower layers, if applicable; 1> apply the LTM configuration in UE-LTM-Config within VarLTM-UE-Config related to the LTM candidate cell configuration identity as received by lower layers. 1> if the value of field Itm-NoResetID contained within the LTM-Candidate IE related to the LTM candidate cell configuration identity (Target configuration ID) as received by lower layers (i.e. MAC layer) is equal to the value of Itm-ServingCellNoResetlD within VarLTM-ServingCellNoResetlD: 2> continue using the current RLC entity in the LTM candidate cell configuration indicated by lower layers; 2> replace the value of Itm-ServingCellNoResetID in VarLTM-ServingCellNoResetID with the value received within Itm-NoResetlD: 1> else: 2> for each RLC-BearerConfig within rlc-BearerToAddModList that is part of current UE configuration: 3> re-establish the RLC entity; 2> for each drb-ldentity value included in the drb-ToAddModList that is part of the current UE configuration: 3> trigger the PDCP entity of this DRB to perform data recovery; 2> replace the value of Itm-ServingCellNoResetID in VarLTM-ServingCellNoResetID with the value received within Itm-NoResetID; 1> continue using the current PDCP entity in the LTM candidate cell configuration(Target configuration ID) indicated by lower layers (i.e. MAC layer);1> apply the LTM configuration in ue-LTM-Config within VarLTM-UE-Config related to the LTM candidate cell configuration identity as received from lower layers; 1> consider the LTM candidate cell indicated by lower layers to be the serving cell; 1> if the RRCReconfiguration message including the LTM-Candidate IE related to the LTM candidate cell configuration identity (Target configuration ID) as received by lower layers (i.e. MAC layer) was received via SRB1 within the nr-SCG within mrdc-SecondaryCellGroup (UE in NR-DC): 2> submit the RRCReconfigurationComplete message via the NR MCG embedded in NR RRC message ULInformationTransferMRDC: 1> else if RRCReconfiguration message including the LTM-Candidate IE related to the LTM candidate cell configuration identity as received by lower layers was received via SRB3 (UE in NR-DC): 2> submit the RRCReconfigurationComplete message via SRB3 to lower layers for transmission using the new configuration; 1> else (RRCReconfiguration was received via SRB1): 2> submit the RRCReconfigurationComplete message to lower layers for transmission via SRB1 using the new configuration.submit the RRCReconfigurationComplete message to lower layers for transmission using the new configuration. Option 2: In this option, if UE receives the first MAC CE and is going to initiate the LTM cell switch procedure when T316 is running, then UE does not perform the LTM cell switch procedure as the LTM cell switch procedure may be difficult to be controlled by the CU of the MCG. The LTM cell switch can be triggered by DU of the MCG, which may cause misalignment between CU and DU. Note that LTM cell switch can be performed within a cell group. As the running of T316 indicates MCG (Master cell group) radio link failure, UE can wait the response from MCG in the MCG failure recovery procedure, rather than performing LTM cell candidate procedure. The corresponding procedure is as follows. Upon the indication by lower layers that an LTM cell switch procedure is triggered, if T316 is not running (while T316 is not running), the UE shall: 1> release / clear all current dedicated radio configuration except for the following: 2> if the LTM cell switch is triggered on the MCG: the MCG C-RNTI; UE needs to maintain or keep the MCG C-RNTI upon the indication by lower layers that an LTM cell switch procedure is triggered on the MCG as UE may use this RNTI at RLE or at RRC Re-establishent procedure, which can occur during LTM scell switch procedure. the AS security configurations associated with the master key; 2> else, if the LTM cell switch is triggered on the SCG: UE doesn’t have to keep the SCG C-RNTI as there is no use case for this RNTI during LTM scell switch procedure, (i.e. UE discards (or releases or clears) SCG C-RNTI upon the indication by lower layers that an LTM cell switch procedure is triggered on the SCG)-the AS security configurations associated with the secondary key; the SRB1 / SRB2 configurations and DRB configurations as configured by radioBearerConfig or radioBearerConfig2; the UE variables VarLTM-Config and VarLTM-UE-Config. 1> release / clear all current common radio configuration associated with the cell group for which the LTM cell switch procedure is triggered; 1> use the default values specified for timers T310, T311 and constants N310, N311 associated with the cell group for which the LTM cell switch procedure is triggered; 1> apply the default L1 parameter values as specified in corresponding physical layer specifications except for the following: parameters for which values are provided in SIB1 (i.e. system information); 1 >apply the value of the newUE-ldentity as the C-RNTI for this cell group according to the LTM candidate cell configuration related to the the LTM candidate cell configuration identity as received by lower layers; 1> configure lower layers in accordance with the received spCellConfigCommon according to the LTM candidate cell configuration indicated by lower layers; 1> configure lower layers in accordance with the received rach-ConfigDedicated according to the LTM candidate cell configuration indicated by lower layers. 1> configure the PDCP entity for LTM candidate cell configuration indicated by lower layers with state variables continuation for SRBs, and with the same security configuration as the PDCP entity for the source cell group; 1 >stop timer T310 for the corresponding SpCell, if running; 1> if this procedure is executed for the MCG: 2> if timer T316 is running; 3> stop timer T316; 1 >stop timer T312 for the corresponding SpCell, if running; 1> start timer a supervisor timer (i.e. T3xx) for this cell group with the timer value set to the configured value in RRCReconfiguration, as included within the field Itm-Timers; 1> reset the MAC entity of this cell group; 1> apply the specified BCCH configuration for the target LTM candidate cell configuration; 1> acquire the MIB of the target SpCell as indicated in the LTM candidate cell configuration indicated by lower layers, if applicable; 1> apply the LTM configuration in UE-LTM-Config within VarLTM-UE-Config related to the LTM candidate cell configuration identity as received by lower layers. 1> if the value of field Itm-NoResetID contained within the LTM-Candidate IE related to the LTM candidate cell configuration identity (Target configuration ID) as received by lower layers (i.e. MAC layer) is equal to the value of Itm-ServingCellNoResetID within VarLTM-ServingCellNoResetlD: 2> continue using the current RLC entity in the LTM candidate cell configuration indicated by lower layers; 2> replace the value of Itm-ServingCellNoResetID in VarLTM-ServingCellNoResetID with the value received within Itm-NoResetID; 1> else: 2> for each RLC-BearerConfig within rlc-BearerToAddModList that is part of current UE configuration: 3> re-establish the RLC entity; 2> for each drb-ldentity value included in the drb-ToAddModList that is part of the current UE configuration: 3> trigger the PDCP entity of this DRB to perform data recovery; 2> replace the value of Itm-ServingCellNoResetID in VarLTM-ServingCellNoResetID with the value received within Itm-NoResetID; 1> continue using the current PDCP entity in the LTM candidate cell configuration(Target configuration ID) indicated by lower layers (i.e. MAC layer);1 >apply the LTM configuration in ue-LTM-Config within VarLTM-UE-Config related to the LTM candidate cell configuration identity as received from lower layers; 1> consider the LTM candidate cell indicated by lower layers to be the serving cell; 1> if the RRCReconfiguration message including the LTM-Candidate IE related to the LTM candidate cell configuration identity (Target configuration ID) as received by lower layers (i.e. MAC layer) was received via SRB1 within the nr-SCG within mrdc-SecondaryCellGroup (UE in NR-DC): 2> submit the RRCReconfigurationComplete message via the NR MCG embedded in NR RRC message ULInformationTransferMRDC; 1> else if RRCReconfiguration message including the LTM-Candidate IE related to the LTM candidate cell configuration identity as received by lower layers was received via SRB3 (UE in NR-DC): 2> submit the RRCReconfigurationComplete message via SRB3 to lower layers for transmission using the new configuration; 1> else (RRCReconfiguration was received via SRB1): 2> submit the RRCReconfigurationComplete message to lower layers for transmission via SRB1 using the new configuration.submit the RRCReconfigurationComplete message to lower layers for transmission using the new configuration. For the above options, UE can stop T310 and T312 when LTM execution is initiated as these timers are used to monitor radio link. For example, UE starts T310 upon detecting physical layer problems for the SpCell i.e. upon receiving pre-configured number of consecutive out-of-sync indications from lower layers, stops it upon receiving several consecutive in-sync indications from lower layers for the SpCell, upon receiving RRCReconfiguration with reconfigurationWithSync forthat cell group, upon reception of MobilityFromNRCommand, upon the reconfiguration of rlf-TimersAndConstant, upon initiating the connection re-establishment procedure, upon conditional reconfiguration execution i.e. when applying a stored RRCReconfiguration message including reconfigurationWithSync for that cell group, upon initiating the MCG failure information procedure, and upon LTM cell switch execution. For example, UE starts T312 if T312 is configured in MCG, upon triggering a measurement report for a measurement identity for which T312 has been configured and useT312 value has been set to true, while T310 in PCell is running and UE stops T312 upon receiving pre-configured number of consecutive in-sync indications from lower layers for the SpCell, receiving RRCReconfiguration with reconfigurationWithSync for that cell group, upon reception of MobilityFromNRCommand, upon initiating the RRC re-establishment procedure, upon the reconfiguration of rlf-TimersAndConstant, upon initiating the MCG failure information procedure, upon conditional reconfiguration execution i.e. when applying a stored RRCReconfiguration message including reconfigurationWithSync for that cell group, upon the expiry of T310 in corresponding SpCell, upon SCG release, if the T312 is kept in SCG, if T312 is configured in SCG and useT312 has been set to true, upon triggering a measurement report for a measurement identity for which T312 has been configured, or and upon LTM cell switch execution or while T310 in PSCell is running. For the sake of completeness, Figure 3 shows a flowchart representing a method according to the invention. At S101, a UR is communicatively connected in a Dual Connectivity , DC, configuration to a Master Node, MN, or master Cell Group, MCG, and a Secondary Node, SN, or Secondary Cell Group, SCG, At S102, a determination is made if LTM is triggered for MN / MCG or SN / SCG. If triggered for MN / MCG, then, at S103, the UE maintains MCG Cell-Radio Network Temporary Identifier, C-RNTI, and clears or releases other current dedicated radio configurations associated with a cell group for which the LTM procedure is triggered. If triggered for Sn / SCG, then, at S104, the UE clears or releases current dedicated radio configuration associated with a cell group for which the LTM procedure is triggered. At least some of the example embodiments described herein may be constructed, partially or wholly, using dedicated special-purpose hardware. Terms such as ‘component’, ‘module’ or ‘unit’ used herein may include, but are not limited to, a hardware device, such as circuitry in the form of discrete or integrated components, a Field Programmable Gate Array (FPGA) or Application Specific Integrated Circuit (ASIC), which performs certain tasks or provides the associated functionality. In some embodiments, the described elements may be configured to reside on a tangible, persistent, addressable storage medium and may be configured to execute on one or more processors. These functional elements may in some embodiments include, by way of example, components, such as software components, object-oriented software components, class components and task components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. Although the example embodiments have been described with reference to the components, modules and units discussed herein, such functional elements may be combined into fewer elements or separated into additional elements. Various combinations of optional features have been described herein, and it will be appreciated that described features may be combined in any suitable combination. In particular, the features of any one example embodiment may be combined with features of any other embodiment, as appropriate, except where such combinations are mutually exclusive. Throughout this specification, the term “comprising” or “comprises” means including the component(s) specified but not to the exclusion of the presence of others. Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. 5 Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. 10 The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. 15

Claims

1. A method of performing L1 / L2 Triggered Mobility, LTM, in a User Equipment, UE, communicatively connected in a Dual Connectivity , DC, configuration to a Master Node, MN, or master Cell Group, MCG, and a Secondary Node, SN, or Secondary Cell Group, SCG, wherein:if LTM is triggered for the MN or MCG, then the UE maintains MCG Cell-Radio Network Temporary Identifier, C-RNTI, and clears or releases other current dedicated radio configurations associated with a cell group for which the LTM procedure is triggered; orif LTM is triggered for the SN or SCG, then the UE clears or releases current dedicated radio configuration associated with a cell group for which the LTM procedure is triggered2. The method of claim 1 wherein if LTM is triggered for the MN or MCG, then one of the other current dedicated radio configurations associated with a cell group for which the LTM procedure is triggered includes SCG C-RNTI.

3. The method of any preceding claim wherein if LTM is triggered for the SN or SCG, then conditions for parameters set in an RRC message and instructions of a lower layer are satisfied only to trigger a random access procedure.

4. The method of any preceding claim wherein, upon receipt of an RRCReconfiguration message by the UE, determining if scg-State is included in the RRCReconfiguration message and if not, determining if reconfigurationWihSync is included in spCellConfig in nr-SCG and if the RRCReconfiguration message is not applied due to an LTM cell switch execution for which a lower layer indicates to skip the Random Access procedure, then initiate a Random Access procedure on the PSCell.

5. Apparatus arranged to perform the method of any preceding claim.

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