5G NR UE Timers and Constants
Below is the list of all the UE Timers and Constants in the 5G NR. All descriptions have been copied from the spec and have not been modified to keep the original information handy for a quick search.
| Timer | Start | Stop | At expiry |
|---|---|---|---|
| T300 | Upon transmission of RRCSetupRequest. | “Upon reception of RRCSetup or RRCReject message, cell re-selection and upon abortion of connection establishment by upper layers.” | Perform the actions as specified in 5.3.3.7.[3GPP TS 38.331] |
| T301 | Upon transmission of RRCReestabilshmentRequest | Upon reception of RRCReestablishment or RRCSetup message as well as when the selected cell becomes unsuitable | Go to RRC_IDLE |
| T302 | “Upon reception of RRCReject while performing RRC connection establishment or resume, upon reception of RRCRelease with waitTime.” | “Upon entering RRC_CONNECTED or RRC_IDLE, upon cell re-selection and upon reception of RRCReject message.” | Inform upper layers about barring alleviation as specified in 5.3.14.4 [3GPP TS 38.331] |
| T304 | Upon reception of RRCReconfiguration message including reconfigurationWithSync or upon conditional reconfiguration execution i.e. when applying a stored RRCReconfiguration message including reconfigurationWithSync. | “Upon successful completion of random access on the corresponding SpCell . For T304 of SCG, upon SCG release” | “For T304 of MCG, in case of the handover from NR or intra-NR handover, initiate the RRC re-establishment procedure; In case of handover to NR, perform the actions defined in the specifications applicable for the source RAT. If any DAPS bearer is configured and if there is no RLF in source PCell, initiate the failure information procedure. For T304 of SCG, inform network about the reconfiguration with sync failure by initiating the SCG failure information procedure as specified in 5.7.3.”[3GPP TS 38.331] |
| T310 | Upon detecting physical layer problems for the SpCell i.e. upon receiving N310 consecutive out-of-sync indications from lower layers. | “Upon receiving N311 consecutive in-sync indications from lower layers for the SpCell, upon receiving RRCReconfiguration with reconfigurationWithSync for that 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, and upon initiating the MCG failure information procedure.” | “If the T310 is kept in MCG: If AS security is not activated: go to RRC_IDLE else: initiate the MCG failure information procedure as specified in 5.7.3b[3GPP TS 38.331] or the connection re-establishment procedure as specified in 5.3.7 or the procedure as specified in 5.3.10.3 [3GPP TS 38.331] if any DAPS bearer is configured. If the T310 is kept in SCG, Inform E-UTRAN/NR about the SCG radio link failure by initiating the SCG failure information procedure as specified in 5.7.3.”[3GPP TS 38.331] |
| T311 | Upon initiating the RRC connection re-establishment procedure | Upon selection of a suitable NR cell or a cell using another RAT. | Enter RRC_IDLE |
| T312 | “If T312 is configured in MCG: Upon triggering a measurement report for a measurement identity for which T312 has been configured and useT312 has been set to true, while T310 in PCell is running. 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, while T310 in PSCell is running.” | “Upon receiving N311 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 connection 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, and upon the expiry of T310 in corresponding SpCell. Upon SCG release, if the T312 is kept in SCG” | “If the T312 is kept in MCG initiate the MCG failure information procedure as specified in 5.7.3b or the connection re-establishment procedure. If the T312 is kept in SCG, Inform E-UTRAN/NR about the SCG radio link failure by initiating the SCG failure information procedure.as specified in 5.7.3.”[3GPP TS 38.331] |
| T316 | Upon transmission of the MCGFailureInformation message | “Upon receiving RRCRelease, RRCReconfiguration with reconfigurationwithSync for the PCell, MobilityFromNRCommand, or upon initiating the re-establishment procedure” | Perform the actions as specified in 5.7.3b.5.[3GPP TS 38.331] |
| T319 | Upon transmission of RRCResumeRequest or RRCResumeRequest1. | “Upon reception of RRCResume, RRCSetup, RRCRelease, RRCRelease with suspendConfig or RRCReject message and upon cell re-selection.” | Perform the actions as specified in 5.3.13.5.[3GPP TS 38.331] |
| T320 | Upon reception of t320 or upon cell (re)selection to NR from another RAT with validity time configured for dedicated priorities (in which case the remaining validity time is applied). | “Upon entering RRC_CONNECTED, upon reception of RRCRelease, when PLMN selection or SNPN selection is performed on request by NAS, when the UE enters RRC_IDLE from RRC_INACTIVE, or upon cell (re)selection to another RAT (in which case the timer is carried on to the other RAT).” | Discard the cell reselection priority information provided by dedicated signalling. |
| T321 | Upon receiving measConfig including a reportConfig with the purpose set to reportCGI | “Upon acquiring the information needed to set all fields of cgi-info, upon receiving measConfig that includes removal of the reportConfig with the purpose set to reportCGI and upon detecting that a cell is not broadcasting SIB1.” | “Initiate the measurement reporting procedure, stop performing the related measurements.” |
| T322 | Upon receving measConfig including reportConfigNR with the purpose set to reportSFTD and drx-SFTD-NeighMeas is set to true. | “Upon acquiring the SFTD measurement results, upon receiving measConfig that includes removal of the reportConfig with the purpose set to reportSFTD.” | “Initiate the measurement reporting procedure, stop performing the related measurements.” |
| T325 | Upon reception of RRCRelease message with deprioritisationTimer. | Stop deprioritisation of all frequencies or NR signalled by RRCRelease. | |
| T330 | Upon receiving LoggedMeasurementConfiguration message | “Upon log volume exceeding the suitable UE memory, upon initiating the release of LoggedMeasurementConfiguration procedure” | Perform the actions specified in 5.5a.1.4[3GPP TS 38.331] |
| T331 | Upon receiving RRCRelease message with measIdleDuration | “Upon receiving RRCSetup, RRCResume, RRCRelease with idle/inactive measurement configuration, upon cell selection/reselection to a cell that does not belong to the validityArea (if configured), or upon cell re-selection to another RAT.” | Perform the actions as specified in 5.7.8.3.[3GPP TS 38.331] |
| T342 | Upon transmitting UEAssistanceInformation message with DelayBudgetReport. | “Upon releasing delayBudgetReportingConfig during the connection re-establishment/resume procedures, and upon receiving delayBudgetReportingConfig set to release.” | No action. |
| T345 | Upon transmitting UEAssistanceInformation message with overheatingAssistance | “Upon releasing overheatingAssistance during the connection re-establishment procedure, upon initiating the connection resumption procedure, and upon receiving overheatingAssistanceConfig set to release.” | No action. |
| T346a | Upon transmitting UEAssistanceInformation message with drx-Preference. | “Upon releasing drx-PreferenceConfig during the connection re-establishment/resume procedures, upon receiving drx-PreferenceConfig set to release, or upon performing MR-DC release.” | No action. |
| T346b | Upon transmitting UEAssistanceInformation message with maxBW-Preference. | “Upon releasing maxBW-PreferenceConfig during the connection re-establishment/resume procedures, upon receiving maxBW-PreferenceConfig set to release, or upon performing MR-DC release.” | No action. |
| T346c | Upon transmitting UEAssistanceInformation message with maxCC-Preference. | “Upon releasing maxCC-PreferenceConfig during the connection re-establishment/resume procedures, upon receiving maxCC-PreferenceConfig set to release, or upon performing MR-DC release.” | No action. |
| T346d | Upon transmitting UEAssistanceInformation message with maxMIMO-LayerPreference. | “Upon releasing maxMIMO-LayerPreferenceConfig during the connection re-establishment/resume procedures, upon receiving maxMIMO-LayerPreferenceConfig set to release, or upon performing MR-DC release.” | No action. |
| T346e | Upon transmitting UEAssistanceInformation message with minSchedulingOffsetPreference. | “Upon releasing minSchedulingOffsetPreferenceConfig during the connection re-establishment/resume procedures, upon receiving minSchedulingOffsetPreferenceConfig set to release, or upon performing MR-DC release.” | No action. |
| T346f | Upon transmitting UEAssistanceInformation message with releasePreference. | “Upon releasing releasePreferenceConfig during the connection re-establishment/resume procedures, or upon receiving releasePreferenceConfig set to release.” | No action. |
| T350 | Upon transmitting DedicatedSIBRequest message with requestedSIB-List and/or requestedPosSIB-List. | “Upon acquiring the requested SIB(s) or posSIB(s), upon releasing onDemandSIB-Request during the connection re-establishment procedures, upon receiving onDemandSIB-Request set to release, upon reception of RRCRelease or upon successful change of PCell while in RRC_CONNECTED.” | No action |
| T380 | Upon reception of t380 in RRCRelease. | “Upon reception of RRCResume, RRCSetup or RRCRelease.” | Perform the actions as specified in 5.3.13.[3GPP TS 38.331] |
| T390 | When access attempt is barred at access barring check for an Access Category. The UE maintains one instance of this timer per Access Category. | “Upon cell (re)selection, upon entering RRC_CONNECTED, upon reception of RRCReconfiguration including reconfigurationWithSync, upon change of PCell while in RRC_CONNECTED, upon reception of MobilityFromNRCommand, or upon reception of RRCRelease.” | Perform the actions as specified in 5.3.14.4.[3GPP TS 38.331] |
| T400 | Upon transmission of RRCReconfigurationSidelink | Upon reception of RRCReconfigurationFailureSidelink or RRCReconfigurationCompleteSidelink | Perform the Sidelink radio link failure related actions as specified in 5.8.9.3.[3GPP TS 38.331] |
Please Note for all below timers the UE maintains one instance of this timer per cell group
T346a
T346b
T346c
T346d
T346e
UE Counters
| Counter | Reset | Incremented | When reaching max value |
|---|---|---|---|
| N310 | -Upon reception of “”in-sync”” indication from lower layers; – Upon receiving RRCReconfiguration with reconfigurationWithSync for that cell group; – Upon initiating the connection re-establishment procedure. |
Upon reception of “”out-of-sync”” from lower layer while the timer T310 is stopped. | Start timer T310 |
| N311 | – Upon reception of “”out-of-sync”” indication from lower layers; – Upon receiving RRCReconfiguration with reconfigurationWithSync for that cell group; – Upon initiating the connection re-establishment procedure. |
Upon reception of the “”in-sync”” from lower layer while the timer T310 is running. | Stop the timer T310. |
UE Constants
| Constant | Usage |
|---|---|
| N310 | “Maximum number of consecutive “”out-of-sync”” indications for the SpCell received from lower layers” |
| N311 | “Maximum number of consecutive “”in-sync”” indications for the SpCell received from lower layers” |
Reference : 3GPP TS 38.331