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srvcc in lte

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SRVCC, or Single Radio Voice Call Continuity, is a technology used in LTE (Long-Term Evolution) networks to enable seamless handover of voice calls from LTE to 2G or 3G networks without interrupting the call. This is particularly important because LTE is a data-only network, and when a user makes or receives a voice call, the system needs to fall back to a circuit-switched network, such as GSM (2G) or WCDMA (3G).

Here's a technical explanation of how SRVCC works in LTE:

  1. Initial Call Setup:
    • When a voice call is initiated on an LTE device, it is initially set up as a VoLTE (Voice over LTE) call, which uses the IP Multimedia Subsystem (IMS) for signaling.
  2. SRVCC Trigger:
    • As the user moves into an area with poor LTE coverage or the LTE signal quality drops below a certain threshold, the network decides to trigger SRVCC. This is typically based on measurements such as signal strength, quality, and load on the LTE network.
  3. IMS Signaling Handover:
    • The IMS core network initiates a handover process to move the voice call from the LTE network to the legacy circuit-switched 2G or 3G network. This handover is done while maintaining the ongoing call.
  4. SRVCC Preparation:
    • The IMS core network communicates with the LTE radio network controller (eNB) to prepare for the handover. This includes coordinating with the legacy MSC (Mobile Switching Center) in the 2G or 3G network.
  5. Bearer and Context Transfer:
    • The IMS core network transfers the bearer context, call state, and other relevant information to the 2G/3G network to ensure that the voice call can seamlessly continue.
  6. Handover Execution:
    • The actual handover occurs, moving the voice call from the LTE network to the 2G/3G network. The handover process minimizes call disruption, ensuring a smooth transition.
  7. Circuit-Switched Voice Call:
    • Once the handover is complete, the voice call is now operating on the legacy circuit-switched network (GSM or WCDMA).
  8. SRVCC Release:
    • After the handover is successful, the IMS core network releases the resources related to the VoLTE call in the LTE network.
  9. Call Continuity:
    • The user experiences no noticeable interruption in the voice call, and the call can continue seamlessly on the 2G or 3G network.

SRVCC is part of the overall voice handover solution, and its successful implementation requires coordination between the LTE and legacy circuit-switched networks, as well as support from the mobile device. This technology is crucial for providing a consistent and reliable voice service in LTE networks, ensuring users can make and receive calls even when moving between different network technologies.