Sign in Subscribe

IRAT Handover From UTRAN Failure

Last updated on 


The IRAT (Inter-Radio Access Technology) Handover From UTRAN (UMTS Terrestrial Radio Access Network) Failure is a technical procedure that occurs when a user equipment (UE) attempts to perform a handover from a UTRAN cell (3G network) to a cell in a different radio access technology, such as LTE (4G) or 5G, but the handover process encounters issues or fails. This procedure is initiated when the network or the UE faces challenges in executing a successful handover. Here's a detailed technical explanation of the IRAT Handover From UTRAN Failure procedure:

1. Handover Trigger:

  • UE Movement and Network Assessment: The trigger for the IRAT handover is when the UE moves from a UTRAN cell's coverage area into an area where a different radio access technology (e.g., LTE or 5G) is available. The network assesses the need for handover based on factors like signal quality and resource availability.

2. Handover Preparation:

  • Target Radio Access Technology Selection: The network selects the target cell in the non-UTRAN radio access technology (e.g., LTE) to which the UE should hand over its connection. This selection is based on criteria such as signal strength, cell load, and quality of service.
  • Resource Allocation: Resources in the target cell are allocated to accommodate the incoming UE's connection.

3. Handover Request:

  • UE Initiates Handover Request: The UE realizes it needs to switch to a different radio access technology and initiates an IRAT Handover From UTRAN Request message. This message is typically sent to the serving UTRAN cell's radio network controller (RNC).

4. RNC Processing:

  • Message Handling: The serving RNC receives the IRAT Handover From UTRAN Request message from the UE and processes it.
  • Verification: The RNC verifies the request's validity and ensures that the UE is allowed to perform an IRAT handover.

5. Handover Failure Detection:

  • Resource Unavailability: If the resources in the target cell are unavailable, or if the target cell is congested, the network may determine that a handover is not feasible.
  • Radio Conditions: Poor radio conditions or interference in the target cell can also lead to handover failure.

6. IRAT Handover From UTRAN Failure Indication:

  • Message Generation: If the network determines that the handover cannot be successfully completed, it generates an IRAT Handover From UTRAN Failure Indication message. This message contains information about the failure cause.
  • Message Signaling: The failure indication is sent to the UE to inform it of the handover failure.

7. UE Processing:

  • Message Reception: The UE receives the IRAT Handover From UTRAN Failure Indication message and processes it.
  • Recovery Actions: The UE may take recovery actions, such as returning to the previous UTRAN cell, performing a different handover attempt, or staying in the current cell.

8. Handover Failure Handling:

  • Network Cleanup: The network may release any allocated resources for the handover attempt and update its handover state accordingly.
  • Handover Retrial: Depending on the specific cause of failure, the network and UE may attempt a handover again after a certain time or under different conditions.

The IRAT Handover From UTRAN Failure procedure is necessary for handling situations where the network or the UE encounters challenges in completing the handover successfully. It ensures that the UE's connection remains stable and provides feedback to the UE and the network about the reason for the handover failure, enabling potential recovery actions.