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Handover Cancel

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Handover Cancel is a procedure in mobile telecommunications networks, such as LTE (Long-Term Evolution) and 5G, that allows for the cancellation or aborting of an ongoing handover process. A handover, also known as a handoff, is the process of transferring an active call or data session from one cell or base station to another to maintain seamless communication as a mobile device moves through the network. The Handover Cancel procedure is initiated in cases where it's determined that the ongoing handover should be terminated due to various reasons, such as network conditions or user-specific requirements. Here's a technical explanation of the Handover Cancel procedure:

1. Handover Trigger:

  • Handover Initiation: A handover is initiated when the network decides that the mobile device should switch to a different cell or base station for better signal quality, load balancing, or other reasons. This initiation may be triggered by network algorithms, resource management policies, or other network conditions.

2. Handover Preparation:

  • Preparation Phase: The network begins the preparation phase for the handover, which includes configuring the target cell or base station, allocating resources, and coordinating with network elements like the Mobility Management Entity (MME) and Serving Gateway (S-GW) in LTE.

3. Handover Execution:

  • Execution Phase: During the execution phase, the mobile device (UE) starts the handover process by establishing a connection with the target cell or base station. Data sessions and communication are gradually transferred from the source to the target cell.

4. Handover Cancellation Trigger:

  • Cancellation Decision: Handover Cancel may be triggered for various reasons, such as poor signal quality in the target cell, the mobile user's request to cancel the handover, network congestion, or changes in network policies.

5. UE Signaling (Handover Cancel Request):

  • UE-to-eNodeB/gNodeB Message: When the decision is made to cancel the handover, the UE sends a Handover Cancel Request message to the serving eNodeB (in LTE) or gNodeB (in 5G). This message indicates the UE's intention to abort the handover.

6. eNodeB/gNodeB Processing:

  • Message Handling: The eNodeB/gNodeB receives the Handover Cancel Request message from the UE and processes it.
  • Handover Cancellation Validation: The eNodeB/gNodeB verifies the validity of the cancellation request, ensuring that it aligns with network policies and that the handover is still in progress.

7. Handover Cancel Signaling (to Core Network):

  • Forwarding to MME: If the eNodeB/gNodeB determines that the cancellation request is valid and should proceed, it forwards the Handover Cancel Request message to the Mobility Management Entity (MME) in the core network.
  • Notification: The eNodeB/gNodeB may send a notification to the target cell or base station, indicating that the handover should not be completed.

8. MME Handling:

  • Cancellation Confirmation: The MME processes the Handover Cancel Request message and validates the cancellation request.
  • Resource Deallocation: The MME initiates the deallocation of resources associated with the handover process, ensuring that resources in the target cell are not allocated.

9. Handover Cancel Confirmation (Handover Cancel Response):

  • MME Confirmation to eNodeB/gNodeB: Once the MME has successfully handled the cancellation request and deallocated resources, it sends a Handover Cancel Response message to the eNodeB/gNodeB.
  • UE Notification: The eNodeB/gNodeB receives the Handover Cancel Response message and forwards it to the UE, notifying the UE that the handover has been canceled.

10. Continued Operation:

  • Post-Cancellation Operation: After the Handover Cancel procedure, the UE continues its communication in the source cell or base station. Further handover decisions may be made based on network conditions or user movements.

The Handover Cancel procedure is essential for ensuring that handovers are executed smoothly and efficiently. It allows for the graceful termination of a handover in cases where it is no longer beneficial or necessary, helping to maintain the quality of service for mobile users.