Sign in Subscribe

How does VoLTE handle handovers between LTE and non-LTE networks?

Last updated on 


Voice over LTE (VoLTE) is a technology that allows voice calls to be transmitted over the Long-Term Evolution (LTE) network, which is an all-IP based system optimized for data transfer. When a VoLTE-enabled device moves between LTE and non-LTE networks (such as 3G or 2G networks), it undergoes a process called a handover to ensure continuity of the voice call.

During a handover between LTE and non-LTE networks in VoLTE, the following technical steps take place:

  1. Initial Call Setup:
    • A VoLTE call is established over the LTE network using an IP Multimedia Subsystem (IMS) architecture.
    • The call session is managed by the IMS core network, which handles signaling and media for VoLTE calls.
  2. Detection of Network Change:
    • As the device moves out of LTE coverage or encounters a situation where LTE coverage is not available or weak, the device monitors the signal strength and quality.
    • Once the device detects that LTE coverage is insufficient, it initiates a network handover procedure.
  3. Handover Decision:
    • The device or the network determines the need for a handover based on predefined thresholds for signal strength or quality.
    • When the device determines that LTE coverage is no longer suitable, it triggers a handover to a compatible non-LTE network (such as 3G or 2G).
  4. Handover Preparation:
    • Before the actual handover, the device and the network perform necessary preparations to ensure a seamless transition of the voice call.
    • This involves setting up the necessary resources and context in the target non-LTE network to continue the call.
  5. Switching to Non-LTE Network:
    • The device switches its connection from LTE to the selected non-LTE network (3G or 2G).
    • The call continues seamlessly over the new network, ensuring minimal interruption to the conversation.
  6. Voice Call Continuation:
    • The IMS core network facilitates the continuity of the voice call over the non-LTE network.
    • The media stream (voice data) is rerouted through the new network while maintaining the call session and ensuring that the call quality is maintained.
  7. Handover Completion:
    • Once the call has successfully transitioned to the non-LTE network, the handover process is completed, and the call continues until the user ends it or another network change occurs.