Terminology » 5G » 5G Timers: UE Timers T300-T312 Explained

5G Timers: UE Timers T300-T312 Explained

5g ue timer rrc wireless communication

This page delves into the 5G timers used at the User Equipment (UE), specifically focusing on timers like T300, T301, T302, T304, T310, T311, and T312, and how they are employed within the 5G wireless system for different functionalities.

5G Timer Functions

Here’s a breakdown of the key 5G timers, detailing their function, start conditions, stop conditions, and what happens upon expiry:

5G TimersFunctionStartStopExpiry
T300Manages the RRC Connection Request procedure.Transmission of RRC Connection Request.Reception of RRC Connection Setup or RRC Connection Reject message, or upon cell selection.- The UE resets MAC, releases MAC configuration, and re-establishes RLC for all established RBs.
- It informs upper layers about the failure to establish an RRC connection, ending the procedure.
T301Oversees the RRC Connection Re-establishment request procedure.Transmission of RRC Connection Re-establishment request.Reception of RRC Connection Re-establishment or RRC Connection Re-establishment Reject message, or when the selected cell becomes unsuitable.The timer leads the UE to transition to RRC_IDLE state.
T302Handles the scenario following the reception of an RRC Connection Reject message during RRC Connection Establishment.Reception of RRC Connection Reject while performing RRC Connection Establishment.Upon entering RRC_CONNECTED or upon cell selection.The UE informs upper layers about barring alleviation for mobile originating data or mobile originating access.
T304Governs the handover process, particularly when Mobility Control Info is involved.Reception of RRC Connection Re-configuration message including Mobility Control Info.As per criteria for successful completion of handover within 5GRA, handover to 5GRA.In case of intra 5GRA handover, it initiates the RRC connection re-establishment procedure.
T310Monitors physical layer problems on the PCell.Detecting physical layer problems for PCell, specifically upon receiving N310 consecutive out-of-sync indications from lower layers.Receiving N311 consecutive in-sync indications from lower layers for PCell, upon triggering the handover procedure, or upon initiating the connection re-establishment procedure.- IF security is not activated, the UE transitions to RRC_IDLE state.
- ELSE, it initiates the connection establishment procedure.
T311Controls the RRC Connection re-establishment procedure.Initiating the RRC Connection re-establishment procedure.Upon selection of a suitable 5GRA cell.The timer transitions the UE to RRC_IDLE state.
T312Deals with measurement reporting triggered while T310 is running.Triggering a measurement report for measurement identity for which T312 has been configured while the T310 timer is running.- Receiving N311 consecutive in-sync indications from lower layers.
- Upon triggering the handover procedure.
- Upon initiating the connection re-establishment procedure.
- Upon the expiry of the T310 timer.		- IF security is not activated, the timer leads to RRC_IDLE state.
- ELSE, it initiates the connection re-establishment procedure.