5.3.7 RRC connection re-establishment

38.3313GPPNRProtocol specificationRadio Resource Control (RRC)Release 17TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

5.3.7.1 General

Figure 5.3.7.1-1: RRC connection re-establishment, successful

Figure 5.3.7.1-2: RRC re-establishment, fallback to RRC establishment, successful

The purpose of this procedure is to re-establish the RRC connection. A UE in RRC_CONNECTED, for which AS security has been activated with SRB2 and at least one DRB/multicast MRB setup or, for IAB, SRB2, may initiate the procedure in order to continue the RRC connection. The connection re-establishment succeeds if the network is able to find and verify a valid UE context or, if the UE context cannot be retrieved, and the network responds with an RRCSetup according to clause 5.3.3.4.

The network applies the procedure e.g as follows:

– When AS security has been activated and the network retrieves or verifies the UE context:

– to re-activate AS security without changing algorithms;

– to re-establish and resume the SRB1;

– When UE is re-establishing an RRC connection, and the network is not able to retrieve or verify the UE context:

– to discard the stored AS Context and release all RBs and BH RLC channels and Uu Relay RLC channels;

– to fallback to establish a new RRC connection.

If AS security has not been activated, the UE shall not initiate the procedure but instead moves to RRC_IDLE directly, with release cause ‘other’. If AS security has been activated, but SRB2 and at least one DRB or multicast MRB or, for IAB, SRB2, are not setup, the UE does not initiate the procedure but instead moves to RRC_IDLE directly, with release cause ‘RRC connection failure’.

5.3.7.2 Initiation

The UE initiates the procedure when one of the following conditions is met:

1> upon detecting radio link failure of the MCG and t316 is not configured, in accordance with 5.3.10; or

1> upon detecting radio link failure of the MCG while SCG transmission is suspended, in accordance with 5.3.10; or

1> upon detecting radio link failure of the MCG while PSCell change or PSCell addition is ongoing, in accordance with 5.3.10; or

1> upon detecting radio link failure of the MCG while the SCG is deactivated, in accordance with 5.3.10; or

1> upon re-configuration with sync failure of the MCG, in accordance with clause 5.3.5.8.3; or

1> upon mobility from NR failure, in accordance with clause 5.4.3.5; or

1> upon integrity check failure indication from lower layers concerning SRB1 or SRB2, except if the integrity check failure is detected on the RRCReestablishment message; or

1> upon an RRC connection reconfiguration failure, in accordance with clause 5.3.5.8.2; or

1> upon detecting radio link failure for the SCG while MCG transmission is suspended, in accordance with clause 5.3.10.3 in NR-DC or in accordance with TS 36.331 [10] clause 5.3.11.3 in NE-DC; or

1> upon reconfiguration with sync failure of the SCG while MCG transmission is suspended in accordance with clause 5.3.5.8.3; or

1> upon SCG change failure while MCG transmission is suspended in accordance with TS 36.331 [10] clause 5.3.5.7a; or

1> upon SCG configuration failure while MCG transmission is suspended in accordance with clause 5.3.5.8.2 in NR-DC or in accordance with TS 36.331 [10] clause 5.3.5.5 in NE-DC; or

1> upon integrity check failure indication from SCG lower layers concerning SRB3 while MCG is suspended; or

1> upon T316 expiry, in accordance with clause 5.7.3b.5; or

1> upon detecting sidelink radio link failure by L2 U2N Remote UE in RRC_CONNECTED, in accordance with clause 5.8.9.3; or

1> upon reception of NotificationMessageSidelink including indicationType by L2 U2N Remote UE in RRC_CONNECTED, in accordance with clause 5.8.9.10; or

1> upon PC5 unicast link release indicated by upper layer at L2 U2N Remote UE in RRC_CONNECTED.

Upon initiation of the procedure, the UE shall:

1> stop timer T310, if running;

1> stop timer T312, if running;

1> stop timer T304, if running;

1> start timer T311;

1> stop timer T316, if running;

1> if UE is not configured with attemptCondReconfig:

2> reset MAC;

2> release spCellConfig, if configured;

2> suspend all RBs, and BH RLC channels for IAB-MT, and Uu Relay RLC channels for L2 U2N Relay UE, except SRB0 and broadcast MRBs;

2> release the MCG SCell(s), if configured;

2> if MR-DC is configured:

3> perform MR-DC release, as specified in clause 5.3.5.10;

2> release delayBudgetReportingConfig, if configured and stop timer T342, if running;

2> release overheatingAssistanceConfig, if configured and stop timer T345, if running;

2> release idc-AssistanceConfig, if configured;

2> release btNameList, if configured;

2> release wlanNameList, if configured;

2> release sensorNameList, if configured;

2> release drx-PreferenceConfig for the MCG, if configured and stop timer T346a associated with the MCG, if running;

2> release maxBW-PreferenceConfig for the MCG, if configured and stop timer T346b associated with the MCG, if running;

2> release maxCC-PreferenceConfig for the MCG, if configured and stop timer T346c associated with the MCG, if running;

2> release maxMIMO-LayerPreferenceConfig for the MCG, if configured and stop timer T346d associated with the MCG, if running;

2> release minSchedulingOffsetPreferenceConfig for the MCG, if configured stop timer T346e associated with the MCG, if running;

2> release rlm-RelaxationReportingConfig for the MCG, if configured and stop timer T346j associated with the MCG, if running;

2> release bfd-RelaxationReportingConfig for the MCG, if configured and stop timer T346k associated with the MCG, if running;

2> release releasePreferenceConfig, if configured stop timer T346f, if running;

2> release onDemandSIB-Request if configured, and stop timer T350, if running;

2> release referenceTimePreferenceReporting, if configured;

2> release sl-AssistanceConfigNR, if configured;

2> release obtainCommonLocation, if configured;

2> release musim-GapAssistanceConfig, if configured and stop timer T346h, if running;

2> release musim-LeaveAssistanceConfig, if configured;

2> release ul-GapFR2-PreferenceConfig, if configured;

2> release scg-DeactivationPreferenceConfig, if configured, and stop timer T346i, if running;

2> release propDelayDiffReportConfig, if configured;

2> release rrm-MeasRelaxationReportingConfig, if configured;

2> release maxBW-PreferenceConfigFR2-2, if configured;

2> release maxMIMO-LayerPreferenceConfigFR2-2, if configured;

2> release minSchedulingOffsetPreferenceConfigExt, if configured;

1> release successHO-Config, if configured;

1> if any DAPS bearer is configured:

2> reset the source MAC and release the source MAC configuration;

2> for each DAPS bearer:

3> release the RLC entity or entities as specified in TS 38.322 [4], clause 5.1.3, and the associated logical channel for the source SpCell;

3> reconfigure the PDCP entity to release DAPS as specified in TS 38.323 [5];

2> for each SRB:

3> release the PDCP entity for the source SpCell;

3> release the RLC entity as specified in TS 38.322 [4], clause 5.1.3, and the associated logical channel for the source SpCell;

2> release the physical channel configuration for the source SpCell;

2> discard the keys used in the source SpCell (the K_gNB key, the K_RRCenc key, the K_RRCint key, the K_UPint key and the K_UPenc key), if any;

1> release sl-L2RelayUE-Config, if configured;

1> release sl-L2RemoteUE-Config, if configured;

1> release the SRAP entity, if configured;

1> if the UE is acting as L2 U2N Remote UE:

2> if the PC5-RRC connection with the U2N Relay UE is determined to be released:

3> indicate upper layers to trigger PC5 unicast link release;

3> perform either cell selection in accordance with the cell selection process as specified in TS 38.304 [20], or relay selection as specified in clause 5.8.15.3, or both;

2> else (i.e., maintain the PC5 RRC connection):

3> consider the connected L2 U2N Relay UE as suitable and perform actions as specified in clause 5.3.7.3a;

NOTE 1: It is up to Remote UE implementation whether to release or keep the current PC5 unicast link.

1> else:

2> perform cell selection in accordance with the cell selection process as specified in TS 38.304 [20].

NOTE 2: For L2 U2N Remote UE, if both a suitable cell and a suitable relay are available, the UE can select either one based on its implementation.

5.3.7.3 Actions following cell selection while T311 is running

Upon selecting a suitable NR cell, the UE shall:

1> ensure having valid and up to date essential system information as specified in clause 5.2.2.2;

1> stop timer T311;

1> if T390 is running:

2> stop timer T390 for all access categories;

2> perform the actions as specified in 5.3.14.4;

1> stop the relay (re)selection procedure, if ongoing;

1> if the cell selection is triggered by detecting radio link failure of the MCG or re-configuration with sync failure of the MCG or mobility from NR failure, and

1> if attemptCondReconfig is configured; and

1> if the selected cell is not configured with CondEventT1, or the selected cell is configured with CondEventT1 and leaving condition has not been fulfilled; and

1> if the selected cell is one of the candidate cells for which the reconfigurationWithSync is included in the masterCellGroup in the MCG VarConditionalReconfig:

2> if the UE supports RLF-Report for conditional handover, set the choCellId in the VarRLF-Report to the global cell identity, if available, otherwise to the physical cell identity and carrier frequency of the selected cell;

2> apply the stored condRRCReconfig associated to the selected cell and perform actions as specified in 5.3.5.3;

NOTE 1: It is left to network implementation to how to avoid keystream reuse in case of CHO based recovery after a failed handover without key change.

1> else:

2> if UE is configured with attemptCondReconfig:

3> reset MAC;

3> release spCellConfig, if configured;

3> release the MCG SCell(s), if configured;

3> release delayBudgetReportingConfig, if configured and stop timer T342, if running;

3> release overheatingAssistanceConfig , if configured and stop timer T345, if running;

3> if MR-DC is configured:

4> perform MR-DC release, as specified in clause 5.3.5.10;

3> release idc-AssistanceConfig, if configured;

3> release btNameList, if configured;

3> release wlanNameList, if configured;

3> release sensorNameList, if configured;

3> release drx-PreferenceConfig for the MCG, if configured and stop timer T346a associated with the MCG, if running;

3> release maxBW-PreferenceConfig for the MCG, if configured and stop timer T346b associated with the MCG, if running;

3> release maxCC-PreferenceConfig for the MCG, if configured and stop timer T346c associated with the MCG, if running;

3> release maxMIMO-LayerPreferenceConfig for the MCG, if configured and stop timer T346d associated with the MCG, if running;

3> release minSchedulingOffsetPreferenceConfig for the MCG, if configured and stop timer T346e associated with the MCG, if running;

3> release rlm-RelaxationReportingConfig for the MCG, if configured and stop timer T346j associated with the MCG, if running;

3> release bfd-RelaxationReportingConfig for the MCG, if configured and stop timer T346k associated with the MCG, if running;

3> release releasePreferenceConfig, if configured and stop timer T346f, if running;

3> release onDemandSIB-Request if configured, and stop timer T350, if running;

3> release referenceTimePreferenceReporting, if configured;

3> release sl-AssistanceConfigNR, if configured;

3> release obtainCommonLocation, if configured;

3> release scg-DeactivationPreferenceConfig, if configured, and stop timer T346i, if running;

3> release musim-GapAssistanceConfig, if configured and stop timer T346h, if running;

3> release musim-LeaveAssistanceConfig, if configured;

3> release propDelayDiffReportConfig, if configured;

3> release ul-GapFR2-PreferenceConfig, if configured;

3> release rrm-MeasRelaxationReportingConfig, if configured;

3> release maxBW-PreferenceConfigFR2-2, if configured;

3> release maxMIMO-LayerPreferenceConfigFR2-2, if configured;

3> release minSchedulingOffsetPreferenceConfigExt, if configured;

3> suspend all RBs, and BH RLC channels for the IAB-MT, except SRB0 and broadcast MRBs;

2> remove all the entries within the MCG VarConditionalReconfig, if any;

2> for each measId, if the associated reportConfig has a reportType set to condTriggerConfig:

3> for the associated reportConfigId:

4> remove the entry with the matching reportConfigId from the reportConfigList within the VarMeasConfig;

3> if the associated measObjectId is only associated to a reportConfig with reportType set to condTriggerConfig:

4> remove the entry with the matching measObjectId from the measObjectList within the VarMeasConfig;

3> remove the entry with the matching measId from the measIdList within the VarMeasConfig;

2> release the PC5 RLC entity for SL-RLC0, if any;

2> start timer T301;

2> apply the default L1 parameter values as specified in corresponding physical layer specifications except for the parameters for which values are provided in SIB1;

2> apply the default MAC Cell Group configuration as specified in 9.2.2;

2> apply the CCCH configuration as specified in 9.1.1.2;

2> apply the timeAlignmentTimerCommon included in SIB1;

2> initiate transmission of the RRCReestablishmentRequest message in accordance with 5.3.7.4;

NOTE 2: This procedure applies also if the UE returns to the source PCell.

Upon selecting an inter-RAT cell, the UE shall:

1> perform the actions upon going to RRC_IDLE as specified in 5.3.11, with release cause ‘RRC connection failure’.

5.3.7.3a Actions following relay selection while T311 is running

Upon selecting a suitable L2 U2N Relay UE, the L2 U2N Remote UE shall:

1> ensure having valid and up to date essential system information as specified in clause 5.2.2.2;

1> stop timer T311;

1> if T390 is running:

2> stop timer T390 for all access categories;

2> perform the actions as specified in 5.3.14.4;

1> stop the cell (re)selection procedure, if ongoing;

1> start timer T301;

1> release the RLC entity for SRB0, if any;

1> establish a SRAP entity as specified in TS 38.351 [66], if no SRAP entity has been established;

1> apply the specified configuration of SL-RLC0 as specified in 9.1.1.4;

1> apply the SDAP configuration and PDCP configuration as specified in 9.1.1.2 for SRB0;

1> initiate transmission of the RRCReestablishmentRequest message in accordance with 5.3.7.4.

5.3.7.4 Actions related to transmission of RRCReestablishmentRequest message

The UE shall set the contents of RRCReestablishmentRequest message as follows:

1> if the procedure was initiated due to radio link failure as specified in 5.3.10.3 or reconfiguration with sync failure as specified in 5.3.5.8.3:

2> set the reestablishmentCellId in the VarRLF-Report to the global cell identity of the selected cell;

1> set the ue-Identity as follows:

2> set the c-RNTI to the C-RNTI used in the source PCell (reconfiguration with sync or mobility from NR failure) or used in the PCell in which the trigger for the re-establishment occurred (other cases);

2> set the physCellId to the physical cell identity of the source PCell (reconfiguration with sync or mobility from NR failure) or of the PCell in which the trigger for the re-establishment occurred (other cases);

2> set the shortMAC-I to the 16 least significant bits of the MAC-I calculated:

3> over the ASN.1 encoded as per clause 8 (i.e., a multiple of 8 bits) VarShortMAC-Input;

3> with the K_RRCint key and integrity protection algorithm that was used in the source PCell (reconfiguration with sync or mobility from NR failure) or of the PCell in which the trigger for the re-establishment occurred (other cases); and

3> with all input bits for COUNT, BEARER and DIRECTION set to binary ones;

1> set the reestablishmentCause as follows:

2> if the re-establishment procedure was initiated due to reconfiguration failure as specified in 5.3.5.8.2:

3> set the reestablishmentCause to the value reconfigurationFailure;

2> else if the re-establishment procedure was initiated due to reconfiguration with sync failure as specified in 5.3.5.8.3 (intra-NR handover failure) or 5.4.3.5 (inter-RAT mobility from NR failure):

3> set the reestablishmentCause to the value handoverFailure;

2> else:

3> set the reestablishmentCause to the value otherFailure;

1> re-establish PDCP for SRB1;

1> if the UE is acting as L2 U2N Remote UE:

2> establish or re-established (e.g. via release and add) SL RLC entity for SRB1;

2> apply the default configuration of SL-RLC1 as defined in 9.2.4 for SRB1;

2> apply the default configuration of PDCP as defined in 9.2.1 for SRB1;

2> establish the SRAP entity and apply the default configuration of SRAP as defined in 9.2.5 for SRB1;

1> else:

2> re-establish RLC for SRB1;

2> apply the default configuration defined in 9.2.1 for SRB1;

1> configure lower layers to suspend integrity protection and ciphering for SRB1;

NOTE: Ciphering is not applied for the subsequent RRCReestablishment message used to resume the connection. An integrity check is performed by lower layers, but merely upon request from RRC.

1> resume SRB1;

1> if ta-Report is configured with value enabled and the UE supports TA reporting:

2> indicate TA report initiation to lower layers;

1> submit the RRCReestablishmentRequest message to lower layers for transmission.

5.3.7.5 Reception of the RRCReestablishment by the UE

The UE shall:

1> stop timer T301;

1> consider the current cell to be the PCell;

1> update the K_gNB key based on the current K_gNB key or the NH, using the received nextHopChainingCount value, as specified in TS 33.501 [11];

1> store the nextHopChainingCount value indicated in the RRCReestablishment message;

1> derive the K_RRCenc and K_UPenc keys associated with the previously configured cipheringAlgorithm, as specified in TS 33.501 [11];

1> derive the K_RRCint and K_UPint keys associated with the previously configured integrityProtAlgorithm, as specified in TS 33.501 [11].

1> request lower layers to verify the integrity protection of the RRCReestablishment message, using the previously configured algorithm and the K_RRCint key;

1> if the integrity protection check of the RRCReestablishment message fails:

2> perform the actions upon going to RRC_IDLE as specified in 5.3.11, with release cause ‘RRC connection failure’, upon which the procedure ends;

1> configure lower layers to resume integrity protection for SRB1 using the previously configured algorithm and the K_RRCint key immediately, i.e., integrity protection shall be applied to all subsequent messages received and sent by the UE, including the message used to indicate the successful completion of the procedure;

1> configure lower layers to resume ciphering for SRB1 using the previously configured algorithm and, the K_RRCenc key immediately, i.e., ciphering shall be applied to all subsequent messages received and sent by the UE, including the message used to indicate the successful completion of the procedure;

1> release the measurement gap configuration indicated by the measGapConfig, if configured;

1> release the MUSIM gap configuration indicated by the musim-GapConfig, if configured;

1> release the FR2 UL gap configuration indicated by the ul-GapFR2-Config, if configured;

1> perform the L2 U2N Remote UE configuration procedure in accordance with the received sl-L2RemoteUE-Config as specified in 5.3.5.16;

1> set the content of RRCReestablishmentComplete message as follows:

2> if the UE has logged measurements available for NR and if the RPLMN is included in plmn-IdentityList stored in VarLogMeasReport:

3> include the logMeasAvailable in the RRCReestablishmentComplete message;

3> if Bluetooth measurement results are included in the logged measurements the UE has available for NR:

4> include the logMeasAvailableBT in the RRCReestablishmentComplete message;

3> if WLAN measurement results are included in the logged measurements the UE has available for NR:

4> include the logMeasAvailableWLAN in the RRCReestablishmentComplete message;

2> if the sigLoggedMeasType in VarLogMeasReport is included:

3> if T330 timer is running and the logged measurements configuration is for NR:

4> set sigLogMeasConfigAvailable to true in the RRCReestablishmentComplete message;

3> else:

4> if the UE has logged measurements available for NR:

5> set sigLogMeasConfigAvailable to false in the RRCReestablishmentComplete message;

2> 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-Identity stored in VarConnEstFailReport or in at least one of the entries of VarConnEstFailReportList:

3> include connEstFailInfoAvailable in the RRCReestablishmentComplete message;

2> if the UE has radio link failure or handover failure information available in VarRLF-Report and if the RPLMN is included in plmn-IdentityList stored in VarRLF-Report; or

2> 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-IdentityList stored in VarRLF-Report of TS 36.331 [10]:

3> include rlf-InfoAvailable in the RRCReestablishmentComplete message;

2> if the UE has successful handover information available in VarSuccessHO-Report and if the RPLMN is included in plmn-IdentityList stored in VarSuccessHO-Report:

3> include successHO-InfoAvailable in the RRCReestablishmentComplete message;

1> submit the RRCReestablishmentComplete message to lower layers for transmission;

1> if SIB21 is provided by the PCell:

2> if the UE initiated transmission of an MBSInterestIndication message during the last 1 second preceding detection of radio link failure:

3> initiate transmission of an MBSInterestIndication message in accordance with 5.9.4;

1> the procedure ends.

5.3.7.6 T311 expiry

Upon T311 expiry, the UE shall:

1> if the procedure was initiated due to radio link failure or handover failure:

2> set the noSuitableCellFound in the VarRLF-Report to true;

1> perform the actions upon going to RRC_IDLE as specified in 5.3.11, with release cause ‘RRC connection failure’.

5.3.7.7 T301 expiry or selected cell/L2 U2N Relay UE no longer suitable

The UE shall:

1> if timer T301 expires; or

1> if the selected cell becomes no longer suitable according to the cell selection criteria as specified in TS 38.304 [20]; or

1> if the (re)selected L2 U2N Relay UE becomes unsuitable; or

1> upon receiption of NotificationMessageSidelink indicating relayUE-HO or relayUE-CellReselection:

2> perform the actions upon going to RRC_IDLE as specified in 5.3.11, with release cause ‘RRC connection failure’.

5.3.7.8 Reception of the RRCSetup by the UE

The UE shall:

1> perform the RRC connection establishment procedure as specified in 5.3.3.4.