T304 RRC Timer in 5G NR
T304 RRC Timer in 5G NR
The T304 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 Handover. Understanding the exact behaviour of this timer is essential for optimizing network performance, mobility, and radio link recovery.
Purpose and Overview
- Purpose: Handover execution timer
- Description: Maximum time to complete handover execution after receiving RRCReconfiguration with reconfigurationWithSync
Timer Specifications
- Typical Value: 2000 ms
- Allowed Values (ms): 50, 100, 150, 200, 500, 1000, 2000, 4000, 8000, 10000
- Value Range: 50 ms to 10000 ms
- 3GPP Specification Reference: 3GPP TS 38.331 Section 5.3.5
Operational Triggers
Started When
UE receives RRCReconfiguration with reconfigurationWithSync (handover command)
From TS 38.331: Upon reception of RRCReconfiguration message including reconfigurationWithSync or upon conditional reconfiguration execution.
Stopped When
Successful RACH to target cell, or T304 expires
From TS 38.331: Upon successful completion of random access on the corresponding SpCell. For T304 of SCG, upon SCG release.
At Expiry
UE fails to access target cell within timer duration Actions Taken: Handover failure, UE initiates RRC reestablishment procedure, informs upper layers
From TS 38.331: For T304 of MCG: Initiate RRC re-establishment (Intra-NR) or failure information (DAPS). For T304 of SCG: Initiate SCG failure information procedure.
Related Parameters
- Related Timers: T301, T310, T311
- Related Counters: N304
- Associated Procedures: Handover, Inter-cell Mobility, Random Access to Target Cell, CHO (Conditional Handover), DAPS (Dual Active Protocol Stack)
Troubleshooting Tips
If you are observing anomalies or frequent expirations related to the T304 timer, consider checking the following:
- Check target cell SSB RSRP/SINR levels
- Verify target cell PRACH configuration
- Analyze handover preparation delays
- Check for handover command transmission issues
- Review target cell load and availability
- Verify UE beam management at target cell
- Check CHO configuration if applicable
- Review DAPS configuration for mobility
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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