T311 RRC Timer in 5G NR

The T311 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: RRC Re-establishment opportunity timer
Description: Time to find suitable cell for RRC reestablishment after radio link failure

Timer Specifications

Typical Value: 3000 ms
Allowed Values (ms): 1000, 3000, 5000, 10000, 15000, 20000, 30000
Value Range: 1000 ms to 30000 ms
3GPP Specification Reference: 3GPP TS 38.331 Section 5.3.7

Operational Triggers

Started When

T310 expires (RLF declared) or handover failure or integrity check failure or RLC failure

From TS 38.331: Upon initiating the RRC connection re-establishment procedure.

Stopped When

Suitable cell found (starts RRC reestablishment), or T311 expires

From TS 38.331: Upon selection of a suitable NR cell or a cell using another RAT.

At Expiry

No suitable cell found within timer duration Actions Taken: UE enters RRC_IDLE, releases all resources, connection lost (UE must re-register)

From TS 38.331: Enter RRC_IDLE.

Related Timers: T310, T301
Related Counters: N311
Associated Procedures: Radio Link Failure Recovery, Cell Selection, RRC Reestablishment, Beam-based Cell Selection

Troubleshooting Tips

If you are observing anomalies or frequent expirations related to the T311 timer, consider checking the following:

Critical recovery timer! Check cell reselection performance
Verify neighbor cell configuration completeness
Analyze inter-frequency measurements availability
Check S-criteria for suitable cell selection
Review network coverage gaps or holes
Consider longer T311 in sparse networks
Verify UE stored contexts at target cells
Check beam-based cell selection performance
Review SSB-based cell quality thresholds