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volte to vowifi handover call flow

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Voice over LTE (VoLTE) and Voice over Wi-Fi (VoWiFi) are technologies used to make voice calls over LTE and Wi-Fi networks, respectively. Handover between VoLTE and VoWiFi is a seamless transition to ensure continuous call connectivity as a user moves from one network type to another. Below is a technical explanation of the VoLTE to VoWiFi handover call flow:

VoLTE to VoWiFi Handover Call Flow:

  1. Initial VoLTE Call Setup:
    • The user initiates a voice call using VoLTE over an LTE network.
    • The call setup message (SIP INVITE) is sent from the user's device to the IMS (IP Multimedia Subsystem) core network.
    • The IMS core network then establishes a media path for the voice call over the LTE network.
  2. Trigger for Handover to VoWiFi:
    • While the VoLTE call is ongoing, the user moves out of LTE coverage or enters an area where Wi-Fi connectivity is stronger.
    • Based on predefined network policies and parameters (e.g., signal strength, user preference), the device decides to hand over the call from VoLTE to VoWiFi.
  3. Initiation of VoWiFi Call:
    • The device detects the availability of a Wi-Fi network and triggers a transition request.
    • The device sends a re-INVITE message to the IMS core network, signaling its intention to switch the ongoing VoLTE call to VoWiFi.
  4. IMS Core Network Processing:
    • Upon receiving the re-INVITE message, the IMS core network acknowledges the request and starts the handover procedure.
    • The IMS core network updates the user's session information, signaling that the call will now be routed over VoWiFi instead of VoLTE.
  5. Establishment of VoWiFi Call:
    • Once the IMS core network acknowledges the handover request, it sends a response (SIP 200 OK) back to the user's device.
    • The device then establishes a media path over the Wi-Fi network for the voice call.
    • The VoLTE-to-VoWiFi handover is now complete, and the user continues the call seamlessly over the Wi-Fi network.
  6. Continuous Monitoring and Quality Assurance:
    • During the call, both the device and the network continuously monitor the quality of the VoWiFi connection.
    • If the Wi-Fi network quality deteriorates below acceptable levels or if the user moves out of Wi-Fi coverage, the system may initiate a handover back to VoLTE or another suitable network.
  7. Call Termination or Handover Back to VoLTE:
    • Once the call is completed or if there's a need to transition back to VoLTE, the process is reversed.
    • The device sends appropriate signaling messages to the IMS core network, indicating the end of the VoWiFi call or the need to switch back to VoLTE.

Conclusion:

The VoLTE to VoWiFi handover call flow involves several signaling and media path establishment procedures between the user's device and the IMS core network. The goal is to provide uninterrupted voice call service by seamlessly transitioning between LTE and Wi-Fi networks based on network conditions and user preferences. Proper coordination and signaling mechanisms ensure that the handover process is smooth and transparent to the end user.