T310 RRC Timer in 5G NR
T310 RRC Timer in 5G NR
The T310 is a critical Radio Resource Control (RRC) timer in 5G New Radio (NR) networks, defined in 3GPP TS 38.331. It falls under the category of Radio Link Failure. Understanding the exact behaviour of this timer is essential for optimizing network performance, mobility, and radio link recovery.
Purpose and Overview
- Purpose: Radio Link Failure detection timer
- Description: Time to declare radio link failure after N310 consecutive out-of-sync indications from L1
Timer Specifications
- Typical Value: 1000 ms
- Allowed Values (ms): 0, 50, 100, 200, 500, 1000, 2000, 4000, 6000
- Value Range: 0 ms to 6000 ms
- 3GPP Specification Reference: 3GPP TS 38.331 Section 5.3.10, TS 38.133
Operational Triggers
Started When
Physical layer indicates N310 consecutive out-of-sync (poor quality) or BFD (Beam Failure Detection)
From TS 38.331: Upon detecting physical layer problems for the SpCell (N310 consecutive out-of-sync indications).
Stopped When
Physical layer indicates N311 consecutive in-sync, or T310 expires, or successful beam recovery
From TS 38.331: Upon receiving N311 consecutive in-sync indications, RRCReconfiguration with reconfigurationWithSync, MobilityFromNRCommand, or upon initiating re-establishment.
At Expiry
Radio link remains out-of-sync for timer duration Actions Taken: Radio Link Failure (RLF) declared, UE starts T311, initiates cell selection for reestablishment
From TS 38.331: If in MCG: Go to RRC_IDLE (if no security) or initiate re-establishment/failure information. If in SCG: Initiate SCG failure information procedure.
Related Parameters
- Related Timers: T311, T301, T316
- Related Counters: N310, N311
- Associated Procedures: Radio Link Monitoring, RLF Detection, RRC Reestablishment, Beam Failure Detection, Beam Failure Recovery
Troubleshooting Tips
If you are observing anomalies or frequent expirations related to the T310 timer, consider checking the following:
- Critical timer! Check SSB-RSRP/SINR degradation patterns
- Analyze physical layer sync status (PDCCH quality)
- Verify N310 threshold configuration (typically 1-10)
- Check for sudden coverage drops or interference
- Review handover margins and trigger thresholds
- Analyze RLF reports for root causes
- Consider increasing T310 in poor RF conditions
- Verify beam failure detection and recovery procedures
- Check BWP (Bandwidth Part) configuration
- Review TCI (Transmission Configuration Indicator) states
Further Reading
WirelessBrew Team
Technical expert at WirelessBrew, specializing in 5G NR, LTE, and wireless system optimization. Committed to providing accurate, 3GPP-compliant engineering tools.
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