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4g to 5g handover call flow

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The handover process from 4G to 5G involves several steps to ensure a seamless transition for the user. Below is a simplified call flow for the handover from 4G LTE to 5G NR (New Radio):

  1. Initial Connection in 4G (LTE):
    • The user equipment (UE) is initially connected to the 4G LTE network and is actively communicating with the evolved NodeB (eNB).
  2. Measurement and Decision:
    • The UE regularly performs measurements on neighboring cells, including 5G NR cells, to assess the quality of the 5G network.
  3. Detection Trigger:
    • Based on the measurement reports, the LTE eNB may decide that a handover to 5G is necessary for improved performance (e.g., better data rates, lower latency).
  4. Handover Request (HO Request):
    • The LTE eNB sends a handover request to the 5G gNB (Next-Generation NodeB), providing information about the UE, its capabilities, and the reason for the handover.
  5. Path Switch (Data Continuity):
    • The LTE eNB starts forwarding data to the 5G gNB while maintaining the existing connection with the UE.
  6. Path Switch Confirmation (Path Switch Request Acknowledgment):
    • The 5G gNB acknowledges the handover request and confirms its readiness to receive the UE.
  7. Radio Resource Configuration in 5G:
    • The 5G gNB configures radio resources for the UE, ensuring that it can communicate seamlessly in the 5G NR.
  8. Handover Command:
    • The LTE eNB sends a handover command to the UE, instructing it to switch to the 5G NR.
  9. UE Preparation and RRC (Radio Resource Control) Reconfiguration:
    • The UE prepares for the handover and reconfigures its radio resources as instructed by the handover command.
  10. Handover Execution:
    • The UE switches its connection to the 5G NR, and data transmission continues in the 5G network.
  11. Path Switch Confirmation (Handover Complete):
    • The 5G gNB sends a confirmation to the LTE eNB that the handover is complete, and the 4G resources can be released.
  12. Release of 4G Resources:
    • The LTE eNB releases the resources allocated for the UE in the 4G network.

The UE is now seamlessly handed over from the 4G LTE network to the 5G NR network, allowing it to benefit from the higher data rates, lower latency, and other advantages of 5G technology. This process is designed to ensure minimal disruption to ongoing communication sessions during the handover. Keep in mind that the actual implementation details can vary between different network deployments and vendors.