5.3.7 RRC connection re-establishment

36.3313GPPEvolved Universal Terrestrial Radio Access (E-UTRA)Protocol specificationRadio Resource Control (RRC)Release 15TS

5.3.7.1 General

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

Figure 5.3.7.1-2: RRC connection re-establishment, failure

The purpose of this procedure is to re-establish the RRC connection, which involves the resumption of SRB1 (SRB1bis for a NB-IoT UE for which AS security has not been activated) operation, the re-activation of security (except for a NB-IoT UE for which AS security has not been activated) and the configuration of only the PCell.

Except for a NB-IoT UE for which AS security has not been activated, a UE in RRC_CONNECTED, for which security has been activated, may initiate the procedure in order to continue the RRC connection. The connection re-establishment succeeds only if the concerned cell is prepared i.e. has a valid UE context. In case E-UTRAN accepts the re-establishment, SRB1 operation resumes while the operation of other radio bearers remains suspended. If AS security has not been activated, the UE does not initiate the procedure but instead moves to RRC_IDLE directly.

When AS security has not been activated, a NB-IoT UE supporting RRC connection re-establishment for the Control Plane CIoT EPS optimisation in RRC_CONNECTED may initiate the procedure in order to continue the RRC connection.

E-UTRAN applies the procedure as follows:

– When AS security has been activated:

– to reconfigure SRB1 and to resume data transfer only for this RB;

– to re-activate AS security without changing algorithms.

– For a NB-IoT UE supporting RRC connection re-establishment for the Control Plane CIoT EPS optimisation, when AS security has not been activated:

– to re-establish SRB1bis and to continue data transfer for this RB.

5.3.7.2 Initiation

The UE shall only initiate the procedure either when AS security has been activated or for a NB-IoT UE supporting RRC connection re-establishment for the Control Plane CIoT EPS optimisation. The UE initiates the procedure when one of the following conditions is met:

1> upon detecting radio link failure, in accordance with 5.3.11; or

1> upon handover failure, in accordance with 5.3.5.6; or

1> upon mobility from E-UTRA failure, in accordance with 5.4.3.5; or

1> except for UP-EDT, upon integrity check failure indication from lower layers concerning SRB1 or SRB2; or

1> upon an RRC connection reconfiguration failure, in accordance with 5.3.5.5; or

1> upon an RRC connection reconfiguration failure, in accordance with TS38.331 [82], clause 5.3.5.5.

NOTE: For UP-EDT, integrity check failure indication from lower layers is handled in accordance with clause 5.3.3.16.

Upon initiation of the procedure, the UE shall:

1> stop timer T310, if running;

1> stop timer T312, if running;

1> stop timer T313, if running;

1> stop timer T307, if running;

1> start timer T311;

1> stop timer T370, if running;

1> release uplinkDataCompression, if configured;

1> suspend all RBs, including RBs configured with NR PDCP, except SRB0;

1> reset MAC;

1> release the MCG SCell(s), if configured, in accordance with 5.3.10.3a;

1> release the SCell group(s), if configured, in accordance with 5.3.10.3d;

1> apply the default physical channel configuration as specified in 9.2.4;

1> except for NB-IoT, for the MCG, apply the default semi-persistent scheduling configuration as specified in 9.2.3;

1> for NB-IoT, release schedulingRequestConfig, if configured;

1> for the MCG, apply the default MAC main configuration as specified in 9.2.2;

1> release powerPrefIndicationConfig, if configured and stop timer T340, if running;

1> release reportProximityConfig, if configured and clear any associated proximity status reporting timer;

1> release obtainLocationConfig, if configured;

1> release idc-Config, if configured;

1> release sps-AssistanceInfoReport, if configured;

1> release measSubframePatternPCell, if configured;

1> release the entire SCG configuration, if configured, except for the DRB configuration (as configured by drb-ToAddModListSCG);

1> if (NG)EN-DC is configured:

2> perform MR-DC release, as specified in TS 38.331[82], clause 5.3.5.10;

2> release p-MaxEUTRA, if configured;

2> release p-MaxUE-FR1, if configured;

2> release tdm-PatternConfig, if configured;

1> release naics-Info for the PCell, if configured;

1> if connected as an RN and configured with an RN subframe configuration:

2> release the RN subframe configuration;

1> release the LWA configuration, if configured, as described in 5.6.14.3;

1> release the LWIP configuration, if configured, as described in 5.6.17.3;

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

1> perform cell selection in accordance with the cell selection process as specified in TS 36.304 [4];

1> release bw-PreferenceIndicationTimer, if configured and stop timer T341, if running;

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

1> release ailc-BitConfig, if configured;

5.3.7.3 Actions following cell selection while T311 is running

Upon selecting a suitable E-UTRA cell, the UE shall:

1> if T309 is running:

2> stop timer T309 for all access categories;

2> perform the actions as specified in 5.3.16.4.

1> if the UE is connected to 5GC and the selected cell is only connected to EPC; or

1> if the UE is connected to EPC and the selected cell is only connected to 5GC:

2> perform the actions upon leaving RRC_CONNECTED as specified in 5.3.12, with release cause ‘RRC connection failure’;

1> else:

2> stop timer T311;

2> start timer T301;

2> apply the timeAlignmentTimerCommon included in SystemInformationBlockType2;

2> if the UE is a NB-IoT UE supporting RRC connection re-establishment for the Control Plane CIoT EPS optimisation and AS security has not been activated; and

2> if cp-reestablishment is not included in SystemInformationBlockType2-NB:

3> perform the actions upon leaving RRC_CONNECTED as specified in 5.3.12, with release cause ‘RRC connection failure’;

2> else:

3> initiate transmission of the RRCConnectionReestablishmentRequest message in accordance with 5.3.7.4;

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

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

1> if the selected cell is a UTRA cell, and if the UE supports Radio Link Failure Report for Inter-RAT MRO, include selectedUTRA-CellId in the VarRLF-Report and set it to the physical cell identity and carrier frequency of the selected UTRA cell;

1> perform the actions upon leaving RRC_CONNECTED as specified in 5.3.12, with release cause ‘RRC connection failure’;

5.3.7.4 Actions related to transmission of RRCConnectionReestablishmentRequest message

Except for NB-IoT, if the procedure was initiated due to radio link failure or handover failure, the UE shall:

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

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

1> except for a NB-IoT UE for which AS security has not been activated, set the ue-Identity as follows:

2> set the c-RNTI to the C-RNTI used in the source PCell (handover and mobility from E-UTRA 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 (handover and mobility from E-UTRA 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 (or VarShortMAC-Input-NB in NB-IoT);

3> with the KRRCint key and integrity protection algorithm that was used in the source PCell (handover and mobility from E-UTRA 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> for a NB-IoT UE for which AS security has not been activated, set the ue-Identity as follows:

2> request upper layers for calculated ul-NAS-MAC and ul-NAS-Count using the cellIdentity indicated in SystemInformationBlockType1-NB of the current cell;

2> set the s-TMSI to the S-TMSI provided by upper layers;

2> set the ul-NAS-MAC to the ul-NAS-MAC value provided by upper layers;

2> set the ul-NAS-Count to the ul-NAS-Count value provided by upper layers;

1> set the reestablishmentCause as follows:

2> if the re-establishment procedure was initiated due to reconfiguration failure as specified in 5.3.5.5 (the UE is unable to comply with the reconfiguration):

3> set the reestablishmentCause to the value reconfigurationFailure;

2> else if the re-establishment procedure was initiated due to handover failure as specified in 5.3.5.6 (intra-LTE handover failure) or 5.4.3.5 (inter-RAT mobility from EUTRA failure):

3> set the reestablishmentCause to the value handoverFailure;

2> else:

3> set the reestablishmentCause to the value otherFailure;

1> if the UE is a NB-IoT UE:

2> if the UE supports DL channel quality reporting and cqi-Reporting is present in SystemInformationBlockType2-NB:

3> set the cqi-NPDCCH to include the latest results of the downlink channel quality measurements of the serving cell as specified in TS 36.133 [16];

NOTE: The downlink channel quality measurements may use measurement period T1 or T2, as defined in TS 36.133 [16]. In case period T2 is used the RRC-MAC interactions are left to UE implementation.

2> set earlyContentionResolution to TRUE;

The UE shall submit the RRCConnectionReestablishmentRequest message to lower layers for transmission.

5.3.7.5 Reception of the RRCConnectionReestablishment by the UE

NOTE 1: Prior to this, lower layer signalling is used to allocate a C-RNTI. For further details see TS 36.321 [6];

The UE shall:

1> stop timer T301;

1> consider the current cell to be the PCell;

1> except for a NB-IoT UE for which AS security has not been activated:

2> if SRB1 was configured with NR PDCP and the UE is connected to EPC:

3> for SRB1, release the NR PDCP entity and establish an E-UTRA PDCP entity with the current (MCG) security configuration;

NOTE 1a: The UE applies the LTE ciphering and integrity protection algorithms that are equivalent to the previously configured NR security algorithms.

2> else:

3> for SRB1, re-establish the PDCP entity;

2> re-establish RLC for SRB1;

2> perform the radio resource configuration procedure in accordance with the received radioResourceConfigDedicated and as specified in 5.3.10;

2> resume SRB1;

NOTE 2: E-UTRAN should not transmit any message on SRB1 prior to receiving the RRCConnectionReestablishmentComplete message.

2> if UE is connected to EPC, update the KeNB key based on the KASME key to which the current KeNB is associated, using the nextHopChainingCount value indicated in the RRCConnectionReestablishment message, as specified in TS 33.401 [32];

2> else if UE is connected to 5GC, update the KeNB key based on the KAMF key to which the current KeNB is associated, using the nextHopChainingCount value indicated in the RRCConnectionReestablishment message, as specified in TS 33.501 [86];

2> store the nextHopChainingCount value;

2> derive the KRRCint key associated with the previously configured integrity algorithm, as specified in TS 33.401 [32];

2> derive the KRRCenc key and the KUPenc key associated with the previously configured ciphering algorithm, as specified in TS 33.401 [32];

2> if connected as an RN:

3> derive the KUPint key associated with the previously configured integrity algorithm, as specified in TS 33.401 [32];

2> configure lower layers to activate integrity protection using the previously configured algorithm and the KRRCint 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;

2> if connected as an RN:

3> configure lower layers to apply integrity protection using the previously configured algorithm and the KUPint key, for subsequently resumed or subsequently established DRBs that are configured to apply integrity protection, if any;

2> configure lower layers to apply ciphering using the previously configured algorithm, the KRRCenc key and the KUPenc 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;

2> if the UE is not a NB-IoT UE:

3> if the UE is connected to EPC:

4> set the content of RRCConnectionReestablishmentComplete message as follows:

5> 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:

6> include the rlf-InfoAvailable;

5> if the UE has MBSFN logged measurements available for E-UTRA and if the RPLMN is included in plmn-IdentityList stored in VarLogMeasReport and if T330 is not running:

6> include logMeasAvailableMBSFN;

5> else if the UE has logged measurements available for E-UTRA and if the RPLMN is included in plmn-IdentityList stored in VarLogMeasReport:

6> include the logMeasAvailable;

6> if Bluetooth measurement results are included in the logged measurements the UE has available and if the RPLMN is included in plmn-IdentityList stored in VarLogMeasReport:

7> include the logMeasAvailableBT;

6> if WLAN measurement results are included in the logged measurements the UE has available and if the RPLMN is included in plmn-IdentityList stored in VarLogMeasReport:

7> include the logMeasAvailableWLAN;

6> if the UE has connection establishment failure information available in VarConnEstFailReport and if the RPLMN is equal to plmn-Identity stored in VarConnEstFailReport:

7> include the connEstFailInfoAvailable;

5> if the UE has flight path information available:

6> include flightPathInfoAvailable;

3> perform the measurement related actions as specified in 5.5.6.1;

3> perform the measurement identity autonomous removal as specified in 5.5.2.2a;

2> else:

3> if the UE supports serving cell idle mode measurements reporting and servingCellMeasInfo is present in SystemInformationBlockType2-NB:

4> set the measResultServCell to include the measurements of the serving cell;

NOTE 2a: The UE includes the latest results of the serving cell measurements as used for cell selection/ reselection evaluation, which are performed in accordance with the performance requirements as specified in TS 36.133 [16].

2> submit the RRCConnectionReestablishmentComplete message to lower layers for transmission;

2> if SystemInformationBlockType15 is broadcast by the PCell:

3> if the UE has transmitted an MBMSInterestIndication message during the last 1 second preceding detection of radio link failure:

4> ensure having a valid version of SystemInformationBlockType15 for the PCell;

4> determine the set of MBMS frequencies of interest in accordance with 5.8.5.3;

4> determine the set of MBMS services of interest in accordance with 5.8.5.3a;

4> initiate transmission of the MBMSInterestIndication message in accordance with 5.8.5.4;

2> if SystemInformationBlockType18 is broadcast by the PCell; and the UE transmitted a SidelinkUEInformation message indicating a change of sidelink communication related parameters relevant in PCell (i.e. change of commRxInterestedFreq or commTxResourceReq, commTxResourceReqUC if SystemInformationBlockType18 includes commTxResourceUC-ReqAllowed or commTxResourceInfoReqRelay if PCell broadcasts SystemInformationBlockType19 including discConfigRelay) during the last 1 second preceding detection of radio link failure; or

2> if SystemInformationBlockType19 is broadcast by the PCell; and the UE transmitted a SidelinkUEInformation message indicating a change of sidelink discovery related parameters relevant in PCell (i.e. change of discRxInterest or discTxResourceReq, discTxResourceReqPS if SystemInformationBlockType19 includes discConfigPS or discRxGapReq or discTxGapReq if the UE is configured with gapRequestsAllowedDedicated set to true or if the UE is not configured with gapRequestsAllowedDedicated and SystemInformationBlockType19 includes gapRequestsAllowedCommon) during the last 1 second preceding detection of radio link failure; or

2> if SystemInformationBlockType21 including sl-V2X-ConfigCommon is broadcast by the PCell; and the UE transmitted a SidelinkUEInformation message indicating a change of V2X sidelink communication related parameters relevant in PCell (i.e. change of v2x-CommRxInterestedFreqList or v2x-CommTxResourceReq) during the last 1 second preceding detection of radio link failure:

3> initiate transmission of the SidelinkUEInformation message in accordance with 5.10.2.3;

1> for a NB-IoT UE for which AS security has not been activated:

2> validate dl-NAS-MAC, as specified in TS 33.401 [32];

2> if dl-NAS-MAC check fails:

3> perform the actions upon leaving RRC_CONNECTED as specified in 5.3.12, with release cause ‘RRC connection failure’, upon which the procedure ends;

2> except for a UE that only supports the Control Plane CIoT EPS optimisation:

3> re-establish PDCP for SRB1;

3> re-establish RLC for SRB1;

2> re-establish RLC for SRB1bis;

2> perform the radio resource configuration procedure in accordance with the received radioResourceConfigDedicated and as specified in 5.3.10;

2> except for a UE that only supports the Control Plane CIoT EPS optimisation:

3> resume SRB1;

2> resume SRB1bis;

NOTE 3: E-UTRAN should not transmit any message on SRB1bis prior to receiving the RRCConnectionReestablishmentComplete message.

2> if the UE supports serving cell idle mode measurements reporting and servingCellMeasInfo is present in SystemInformationBlockType2-NB:

3> set the measResultServCell to include the measurements of the serving cell;

NOTE 4: The UE includes the latest results of the serving cell measurements as used for cell selection/ reselection evaluation, which are performed in accordance with the performance requirements as specified in TS 36.133 [16].

2> submit the RRCConnectionReestablishmentComplete message to lower layers for transmission;

1> the procedure ends;

5.3.7.6 T311 expiry

Upon T311 expiry, the UE shall:

1> perform the actions upon leaving RRC_CONNECTED as specified in 5.3.12, with release cause ‘RRC connection failure’;

5.3.7.7 T301 expiry or selected cell 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 36.304 [4]:

2> perform the actions upon leaving RRC_CONNECTED as specified in 5.3.12, with release cause ‘RRC connection failure’;

5.3.7.8 Reception of RRCConnectionReestablishmentReject by the UE

Upon receiving the RRCConnectionReestablishmentReject message, the UE shall:

1> perform the actions upon leaving RRC_CONNECTED as specified in 5.3.12, with release cause ‘RRC connection failure’;