5G NR RRC Timers and Constants
5G NR RRC timers and constants define the supervision windows and threshold counters used in setup, reject-side wait handling, reconfiguration-with-sync, radio link failure detection, recovery, inactive-mode resume supervision, release-side priority persistence, and access barring behavior.
Start with the active RRC procedure, then check whether the timer or constant explains the UE behavior. In practice, T300, T302, T304, T310, T311, T319, T320, T380, T390, T430, N310, and N311 are the anchors that help most when you need to explain setup delay, reject quiet time, handover timeout, radio link failure, inactive persistence, or resume failure in NR traces.
Quick facts
| Technology | 5G NR |
|---|---|
| Protocol scope | NR RRC timers, counters, and constants used in access, mobility, measurements, release, assistance reporting, and recovery |
| Main spec | 3GPP TS 38.331 |
| Release | Release 18 |
| Reference scope | Timers, counters, and constants |
| Main configuration source | UE-TimersAndConstants in SIB1 plus procedure-specific values such as RejectWaitTime, t304, t320, and t380 |
| Main use | Access supervision, reject wait handling, reconfiguration-with-sync timing, radio link failure detection and recovery, release behavior, measurements, and UE assistance reporting |
Overview
NR RRC timer and constant handling is broader than only the core access timers. It includes setup, reject wait, reconfiguration, radio link failure, resume, release, measurement, assistance-reporting, sidelink, counters, constants, and UE variables.
Some values come from UE-TimersAndConstants in SIB1, such as T300, T301, T310, T311, T319, N310, and N311. Others are procedure-specific, such as T302 from RRCReject, T304 from RRCReconfiguration, T320 and T380 from release-side configuration, and T390 from access-barring behavior.
The layout below keeps the broader RRC reference structure visible, but presents the operational content as one master timer table and one constants table for faster lookup.
Reference Scope
Timers
Timer behavior is defined by start conditions, stop conditions, and expiry actions tied to each RRC procedure.
Counters
Counter behavior defines how thresholds such as N310 and N311 are reset and incremented from lower-layer indications.
Constants
Constant values define the consecutive indication thresholds used in RRC monitoring and recovery behavior.
All constants
N310 and N311 define the out-of-sync and in-sync indication thresholds used in radio link monitoring. They work alongside lower-layer indications and the T310 timer to control when the UE enters or exits the radio link failure path.
Reaching the N310 threshold starts T310, and reaching the N311 threshold stops T310. In practice, radio link failure is best read as a combined timer-and-threshold mechanism rather than as only a single timer value.
| Constant | Meaning | Values | Usage |
|---|---|---|---|
| N310 | Maximum number of consecutive out-of-sync indications used by lower layers before the UE starts T310. | n1, n2, n3, n4, n6, n8, n10, n20 | Used in the radio link failure detection branch together with T310. |
| N311 | Maximum number of consecutive in-sync indications used by lower layers before the UE stops T310. | n1, n2, n3, n4, n5, n6, n8, n10 | Used in the radio link failure recovery branch together with T310. |
All timers
The table below brings together the main operational timers and the wider NR RRC timer set into one lookup.
| Timer | Main procedure context | Source or start | Values or stop | Operational note |
|---|---|---|---|---|
| T300 | RRC connection establishment supervision | Configured in UE-TimersAndConstants from SIB1. | UE-TimersAndConstants values are ms100, ms200, ms300, ms400, ms600, ms1000, ms1500, and ms2000. | Supervises the initial setup branch after the UE sends RRCSetupRequest and waits for RRCSetup or RRCReject. Most visible in RRCSetupRequest, RRCSetup, RRCSetupComplete, and RRCReject. |
| T301 | RRC re-establishment supervision | Configured in UE-TimersAndConstants from SIB1 and reused in RLF handling. | UE-TimersAndConstants values are ms100, ms200, ms300, ms400, ms600, ms1000, ms1500, and ms2000. | Supervises the re-establishment branch after the UE sends RRCReestablishmentRequest and waits for the recovery response. Most useful in re-establishment request and later recovery handling after radio link failure. |
| T302 | Wait before retry after RRCReject | Started from waitTime in RRCReject, not from UE-TimersAndConstants. | RejectWaitTime is INTEGER (1..16), and the value is used as the T302 timer in seconds. | Controls how long the UE waits before retrying after an RRCReject during setup or resume. Most visible in RRCReject and in later retry behavior from RRC_IDLE or RRC_INACTIVE. |
| T304 | Reconfiguration-with-sync and mobility execution | Configured by the t304 field in ReconfigurationWithSync. | ReconfigurationWithSync values are ms50, ms100, ms150, ms200, ms500, ms1000, ms2000, and ms10000. | Supervises the execution window after reconfiguration-with-sync, including handover-style movement and target-side continuation. Most visible in RRCReconfiguration with reconfigurationWithSync and in failure handling when target-side continuation does not complete. |
| T310 | Radio link failure detection timer | Configured in UE-TimersAndConstants or overridden by rlf-TimersAndConstants. | UE-TimersAndConstants values are ms0, ms50, ms100, ms200, ms500, ms1000, and ms2000. | Starts after enough consecutive out-of-sync indications and supervises whether radio link failure should be declared. Most useful in radio link monitoring, re-establishment, and post-handover failure analysis. |
| T311 | Recovery window after radio link failure | Configured in UE-TimersAndConstants or overridden by rlf-TimersAndConstants. | UE-TimersAndConstants values are ms1000, ms3000, ms5000, ms10000, ms15000, ms20000, and ms30000. | Defines how long the UE can stay in the post-failure recovery branch before giving up on re-establishment and moving further out of connected recovery. Most useful in re-establishment, radio link failure, and no-recovery cases after T310 expiry. |
| T319 | RRC resume supervision in RRC_INACTIVE | Configured in UE-TimersAndConstants from SIB1. | UE-TimersAndConstants values are ms100, ms200, ms300, ms400, ms600, ms1000, ms1500, and ms2000. | Supervises the resume path after the UE starts RRCResumeRequest or RRCResumeRequest1. Most visible in RRCResumeRequest, RRCReject after resume, and failure-to-resume cases in RRC_INACTIVE. |
| T320 | Cell reselection priority validity after RRCRelease | Configured by the t320 field inside CellReselectionPriorities. | CellReselectionPriorities t320 values are min5, min10, min20, min30, min60, min120, and min180. | Keeps dedicated or redirected cell reselection priorities valid after release until the UE falls back to broadcast priorities again. Most visible in RRCRelease, idle-mode priority behavior, and resume branches that explicitly stop T320. |
| T380 | Periodic RNA update supervision in RRC_INACTIVE | Configured by the t380 field inside SuspendConfig as PeriodicRNAU-TimerValue. | PeriodicRNAU-TimerValue values are min5, min10, min20, min30, min60, min120, min360, and min720. | Defines the periodic RNA update timing retained when the network releases the UE into RRC_INACTIVE with suspendConfig. Most visible in RRCRelease with suspendConfig and in resume or security-related inactive-mode analysis. |
| T390 | Unified access control barring timer | Calculated from UAC barring time, not from a fixed enumerated timer list. | T390 is computed from the UAC barring time as T390 = (0.7 + 0.6 * rand) * uac-BarringTime. | Holds the UE off from retrying the same barred access category after UAC barring decides the access attempt is not allowed. Most visible in access barring, setup retry suppression, and resume branches that stop T390 when access eventually proceeds. |
| T430 | Serving-cell supervision for essential system information reacquisition | Procedure-driven timer used in essential system information handling rather than the basic UE-TimersAndConstants IE. | T430 is handled as a procedure timer in essential system information behavior rather than one of the standard UE-TimersAndConstants enumerations. | Supervises the serving-cell branch where the UE must reacquire essential system information, especially SIB19-related handling. Most visible when essential system information is missing or when serving-cell specific NTN-related information cannot be maintained cleanly. |
| T312 | Measurement-triggered failure escalation while T310 runs | Triggered for a measurement identity where T312 is configured and useT312 is true while T310 is running. | Stopped by N311 recovery, reconfiguration-with-sync, MobilityFromNRCommand, re-establishment start, reconfiguration of RLF timers, T310 expiry, and related recovery branches. | Initiates MCG failure information or re-establishment for MCG, or SCG failure information for SCG. |
| T316 | MCG failure information supervision | Upon transmission of MCGFailureInformation. | Stopped by RRCRelease, RRCReconfiguration with reconfigurationWithSync for the PCell, MobilityFromNRCommand, or re-establishment start. | Triggers the defined MCG failure information handling. |
| T319a | Resume supervision for SDT | Upon transmission of RRCResumeRequest or RRCResumeRequest1 when the resume procedure is initiated for SDT. | Stopped by RRCResume, RRCSetup, RRCRelease, RRCReject, SDT resume failure, or cell reselection. | Triggers the defined SDT resume failure handling. |
| T321 | reportCGI measurement supervision | Upon receiving measConfig including a reportConfig with reportType set to reportCGI. | Stopped when CGI information is acquired, the reportConfig is removed, or the cell is found not to broadcast SIB1. | Initiates measurement reporting and stops the related measurements. |
| T322 | reportSFTD measurement supervision | Upon receiving measConfig including reportConfigNR with reportType set to reportSFTD and drx-SFTD-NeighMeas set to true. | Stopped when SFTD measurement results are acquired or the reportConfig is removed. | Initiates measurement reporting and stops the related measurements. |
| T325 | Deprioritisation timer after release | Upon reception of RRCRelease with deprioritisationTimer. | Procedure-driven deprioritisation end. | Stops deprioritisation of all frequencies or NR signalled by RRCRelease. |
| T330 | Logged measurement configuration supervision | Upon receiving LoggedMeasurementConfiguration. | Stopped when log volume exceeds suitable UE memory or when LoggedMeasurementConfiguration is released. | Triggers the defined logged measurement handling. |
| T331 | Idle or inactive measurement validity | Upon receiving RRCRelease with measIdleDuration. | Stopped by RRCSetup, RRCResume, new idle or inactive measurement configuration, leaving validityArea, or reselection to another RAT. | Triggers the defined idle or inactive measurement handling. |
| T342 | Delay budget reporting hold-off | Upon transmitting UEAssistanceInformation with DelayBudgetReport. | Stopped when delayBudgetReportingConfig is released during re-establishment or resume, or explicitly set to release. | No action. |
| T345 | Overheating assistance hold-off | Upon transmitting UEAssistanceInformation with overheatingAssistance. | Stopped when overheatingAssistanceConfig is released during re-establishment, at connection resumption start, or set to release. | No action. |
| T346a-T346n | UE assistance reporting hold-off family | Started by UEAssistanceInformation reporting for DRX, bandwidth, component carriers, MIMO layers, scheduling offset, release preference, MUSIM preferences, SCG deactivation, relaxation reporting, UL traffic info, multiRx preference, and capability restriction branches. | Stopped when the corresponding configuration is released during re-establishment or resume, explicitly set to release, or MR-DC release applies for per-cell-group cases. | Usually no action, except T346g which triggers its dedicated follow-up handling. |
| T400 | Sidelink reconfiguration supervision | Upon transmission of RRCReconfigurationSidelink. | Stopped by RRCReconfigurationFailureSidelink or RRCReconfigurationCompleteSidelink. | Triggers sidelink radio link failure related handling. |
| T420 | Indirect path switch supervision | Upon reception of RRCReconfiguration including sl-PathSwitchConfig in the branch without indirect path maintain handling. | Stopped after successful completion toward the target relay path. | Performs the RRC re-establishment procedure. |
| T421 | Indirect path add or change supervision | Upon reception of RRCReconfiguration including sl-IndirectPathAddChange in the branch without indirect path maintain handling. | Stopped after successful completion or on initiation of indirect path failure information. | Performs Failure Information Reporting. |
Where to use this page
Use this page as the common lookup target whenever a 5G RRC message lists Related timers. For example, RRCSetupRequest and RRCSetup point naturally to T300, while RRCReject points to T302 and T319 depending on whether the failure happened during setup or resume.
The same approach works for recovery and troubleshooting. Read radio link failure and re-establishment together with T310, N310, T311, and N311. Read inactive-mode service recovery together with T319 and the paging and service resume troubleshooting guide.
Use T320 and T380 when the issue sits around RRCRelease, inactive entry, or later resume behavior. Use T390 for access-barring quiet periods, and T430 when essential system information reacquisition becomes part of the failure branch.
Use the timer table anchors for less common branches such as T312, T316, T319a, T321, T331, T342, T345, T346a-T346n, T400, T420, and T421.
References
- ETSI TS 138 331 V18.2.0 / 3GPP TS 38.331 Release 18
- 3GPP TS 38.331 Release 18 is the primary specification source for the timer, counter, constant, and UE-variable behavior summarized here.
- UE-TimersAndConstants values are taken from the UE-TimersAndConstants definition and the procedure behavior that uses those values.
- Procedure-specific values such as waitTime, t304, t320, and t380 are read from the corresponding message structures and related behavior.