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5G NR Timers and Constants

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The technical details of 5G NR (New Radio) timers and constants. In 5G NR, timers and constants are essential parameters used for various functions, such as connection establishment, handovers, and radio resource management. Timers help define the timing aspects of different procedures, ensuring efficient operation and reliable communication.

Here are some key 5G NR timers and constants:

  1. T300: RRC Inactive Timer:
    • Purpose: T300 is used to trigger the transition from RRC (Radio Resource Control) Inactive state to the RRC Idle state.
    • Default Value: Typically, T300 is set to 20 seconds.
  2. T301: RRC Connected Timer:
    • Purpose: T301 is used to monitor the continuity of an RRC connection. If no RRC message is received within this timer's duration, the connection is considered lost.
    • Default Value: The default value of T301 is usually 60 seconds.
  3. T310: N310 timer:
    • Purpose: This timer is associated with the measurement of the time between the receipt of the RRCConnectionReconfiguration message and the completion of the reconfiguration procedure.
    • Default Value: T310 is typically set to 1 second.
  4. T311: N311 timer:
    • Purpose: T311 is used for evaluating the time between the start of the UE measurement gap and the reception of an RRCConnectionReconfigurationComplete message.
    • Default Value: The default value for T311 is often set to 100 milliseconds.
  5. T320: Xn Handover Timer:
    • Purpose: T320 is associated with Xn handovers. It defines the time allowed for the source gNB (gNodeB) to complete the handover.
    • Default Value: The default value of T320 is usually 5 seconds.
  6. T321: N2 Handover Timer:
    • Purpose: T321 is associated with N2 handovers. It specifies the time allowed for the source gNB to receive an acknowledgment from the target gNB.
    • Default Value: The default value for T321 is often set to 5 seconds.
  7. T325: UE Context Release Timer:
    • Purpose: T325 is used for releasing the UE context. It defines the time the target gNB waits for the source gNB to confirm the UE context release.
    • Default Value: Typically, T325 is set to 2 seconds.
  8. Constants for Radio Link Monitoring (RLM):
    • A3 Offset: It is an offset applied to the measurement quantity for RLM purposes.
    • A3 Time-to-Trigger: The time duration during which the measurement quantity must exceed the A3 threshold before triggering an event.
  9. Constants for Handover and Mobility:
    • Hysteresis: Used in handover decisions, providing a margin to prevent unnecessary handovers due to small variations in signal quality.
    • Time-to-Trigger (TTT): Time duration for which a certain measurement condition must persist before triggering a handover.

These timers and constants play a crucial role in ensuring the reliable and efficient operation of 5G NR networks by controlling various aspects of connection establishment, maintenance, and handover procedures. The values mentioned here are typical defaults and may be configured based on specific network requirements and conditions.