5.3.8 RRC connection release

38.3313GPPNRProtocol specificationRadio Resource Control (RRC)Release 17TS

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

5.3.8.1 General

Figure 5.3.8.1-1: RRC connection release, successful

The purpose of this procedure is:

– to release the RRC connection, which includes the release of the established radio bearers (except for broadcast MRBs), BH RLC channels, Uu Relay RLC channels, PC5 Relay RLC channels as well as all radio resources; or

– to suspend the RRC connection only if SRB2 and at least one DRB or multicast MRB or, for IAB, SRB2, are setup, which includes the suspension of the established radio bearers (except for broadcast MRBs).

5.3.8.2 Initiation

The network initiates the RRC connection release procedure to transit a UE in RRC_CONNECTED to RRC_IDLE; or to transit a UE in RRC_CONNECTED to RRC_INACTIVE only if SRB2 and at least one DRB or multicast MRB or, for IAB, SRB2, is setup in RRC_CONNECTED; or to transit a UE in RRC_INACTIVE back to RRC_INACTIVE when the UE tries to resume (for resuming a suspended RRC connection or for initiating SDT); or to transit a UE in RRC_INACTIVE to RRC_IDLE when the UE tries to resume (for resuming of a suspended RRC connection or for initiating SDT). The procedure can also be used to release and redirect a UE to another frequency.

5.3.8.3 Reception of the RRCRelease by the UE

The UE shall:

1> delay the following actions defined in this clause 60 ms from the moment the RRCRelease message was received or optionally when lower layers indicate that the receipt of the RRCRelease message has been successfully acknowledged, whichever is earlier;

1> stop timer T380, if running;

1> stop timer T320, if running;

1> if timer T316 is running;

2> stop timer T316;

2> clear the information included in VarRLF-Report, if any;

1> stop timer T350, if running;

1> stop timer T346g, if running;

1> if the AS security is not activated:

2> ignore any field included in RRCRelease message except waitTime;

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

1> if the RRCRelease message includes redirectedCarrierInfo indicating redirection to eutra:

2> if cnType is included:

3> after the cell selection, indicate the available CN Type(s) and the received cnType to upper layers;

NOTE 1: Handling the case if the E-UTRA cell selected after the redirection does not support the core network type specified by the cnType, is up to UE implementation.

2> if voiceFallbackIndication is included:

3> consider the RRC connection release was for EPS fallback for IMS voice (see TS 23.502 [43]);

1> if the RRCRelease message includes the cellReselectionPriorities:

2> store the cell reselection priority information provided by the cellReselectionPriorities;

2> if the t320 is included:

3> start timer T320, with the timer value set according to the value of t320;

1> else:

2> apply the cell reselection priority information broadcast in the system information;

1> if deprioritisationReq is included and the UE supports RRC connection release with deprioritisation:

2> start or restart timer T325 with the timer value set to the deprioritisationTimer signalled;

2> store the deprioritisationReq until T325 expiry;

NOTE 1a: The UE stores the deprioritisation request irrespective of any cell reselection absolute priority assignments (by dedicated or common signalling) and regardless of RRC connections in NR or other RATs unless specified otherwise.

1> if the RRCRelease includes the measIdleConfig:

2> if T331 is running:

3> stop timer T331;

3> perform the actions as specified in 5.7.8.3;

2> if the measIdleConfig is set to setup:

3> store the received measIdleDuration in VarMeasIdleConfig;

3> start timer T331 with the value set to measIdleDuration;

3> if the measIdleConfig contains measIdleCarrierListNR:

4> store the received measIdleCarrierListNR in VarMeasIdleConfig;

3> if the measIdleConfig contains measIdleCarrierListEUTRA:

4> store the received measIdleCarrierListEUTRA in VarMeasIdleConfig;

3> if the measIdleConfig contains validityAreaList:

4> store the received validityAreaList in VarMeasIdleConfig;

1> if the RRCRelease includes suspendConfig:

2> reset MAC and release the default MAC Cell Group configuration, if any;

2> apply the received suspendConfig except the received nextHopChainingCount;

2> if the sdt-Config is configured:

3> for each of the DRB in the sdt-DRB-List:

4> consider the DRB to be configured for SDT;

3> if sdt-SRB2-Indication is configured:

4> consider the SRB2 to be configured for SDT;

3> for each RLC bearer that is not suspended:

4> re-establish the RLC entity as specified in TS 38.322 [4];

3> for SRB2 (if it is resumed) and for SRB1:

4> trigger the PDCP entity to perform SDU discard as specified in TS 38.323 [5];

3> if sdt-MAC-PHY-CG-Config is configured:

4> configure the PCell with the configured grant resources for SDT and instruct the MAC entity to start the cg-SDT-TimeAlignmentTimer;

2> if srs-PosRRC-Inactive is configured:

3> apply the configuration and instruct MAC to start the inactivePosSRS-TimeAlignmentTimer;

NOTE 1b: The Network should provide full configuration to UE for SRS for Positioning in RRC_INACTIVE.

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

2> for each measId of the MCG measConfig and for each measId of the SCG measConfig, if configured, 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> re-establish RLC entities for SRB1;

2> if the RRCRelease message with suspendConfig was received in response to an RRCResumeRequest or an RRCResumeRequest1:

3> stop the timer T319 if running;

3> in the stored UE Inactive AS context:

4> replace the K_gNB and K_RRCint keys with the current K_gNB and K_RRCint keys;

4> replace the nextHopChainingCount with the value of nextHopChainingCount received in the RRCRelease message;

4> replace the cellIdentity with the cellIdentity of the cell the UE has received the RRCRelease message;

4> if the suspendConfig contains the sl-UEIdentityRemote (i.e. the UE is a L2 U2N Remote UE):

5> replace the C-RNTI with the value of the sl-UEIdentityRemote;

5> replace the physical cell identity with the value of the sl-PhysCellId in sl-ServingCellInfo contained in the discovery message received from the connected L2 U2N Relay UE;

4> else:

5> replace the C-RNTI with the C-RNTI used in the cell (see TS 38.321 [3]) the UE has received the RRCRelease message;

5> replace the physical cell identity with the physical cell identity of the cell the UE has received the RRCRelease message;

3> replace the nextHopChainingCount with the value associated with the current K_gNB;

3> stop the timer T319a if running and consider SDT procedure is not ongoing;

2> else:

3> store in the UE Inactive AS Context the nextHopChainingCount received in the RRCRelease message, the current K_gNB and K_RRCintkeys, the ROHC state, the EHC context(s), the UDC state, the stored QoS flow to DRB mapping rules, the application layer measurement configuration, the C-RNTI used in the source PCell, the cellIdentity and the physical cell identity of the source PCell, the spCellConfigCommon within ReconfigurationWithSync of the NR PSCell (if configured) and all other parameters configured except for:

– parameters within ReconfigurationWithSync of the PCell;

– parameters within ReconfigurationWithSync of the NR PSCell, if configured;

– parameters within MobilityControlInfoSCG of the E-UTRA PSCell, if configured;

– servingCellConfigCommonSIB;

– sl-L2RelayUE-Config, if configured;

– sl-L2RemoteUE-Config, if configured;

3> store any previously or subsequently received application layer measurement reports for which no segment, or full message, has been submitted to lower layers for transmission;

NOTE 2: NR sidelink communication/discovery related configurations and logged measurement configuration are not stored as UE Inactive AS Context, when UE enters RRC_INACTIVE.

2> suspend all SRB(s) and DRB(s) and multicast MRB(s), except SRB0 and broadcast MRBs;

2> indicate PDCP suspend to lower layers of all DRBs and multicast MRBs;

2> release the SRAP entity, if configured;

2> if the t380 is included:

3> start timer T380, with the timer value set to t380;

2> if the RRCRelease message is including the waitTime:

3> start timer T302 with the value set to the waitTime;

3> inform upper layers that access barring is applicable for all access categories except categories ‘0’ and ‘2’;

2> if T390 is running:

3> stop timer T390 for all access categories;

3> perform the actions as specified in 5.3.14.4;

2> indicate the suspension of the RRC connection to upper layers;

2> enter RRC_INACTIVE and perform cell selection as specified in TS 38.304 [20];

1> else

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

5.3.8.4 T320 expiry

The UE shall:

1> if T320 expires:

2> if stored, discard the cell reselection priority information provided by the cellReselectionPriorities or inherited from another RAT;

2> apply the cell reselection priority information broadcast in the system information.

5.3.8.5 UE actions upon the expiry of DataInactivityTimer

Upon receiving the expiry of DataInactivityTimer from lower layers while in RRC_CONNECTED, the UE shall:

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

5.3.8.6 T346g expiry

The UE shall:

1> if T346g expires:

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