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single radio voice call continuity

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Single Radio Voice Call Continuity (SRVCC) is a technology used in telecommunications, especially in the context of transitioning voice calls between different network technologies while maintaining an uninterrupted voice call experience. The primary objective of SRVCC is to enable a smooth handover of voice calls from a packet-switched (PS) domain, typically associated with LTE (Long-Term Evolution) or 4G networks, to a circuit-switched (CS) domain, usually associated with 2G or 3G networks. This handover ensures that voice calls remain connected even when moving between areas served by different network technologies. Below are the technical details of SRVCC:

1. Basic Concepts:

  • Packet-Switched (PS) and Circuit-Switched (CS) Domains:
    • In telecommunications, PS is associated with data services, while CS is associated with voice services. SRVCC enables the transition of voice calls from a data-centric network to a voice-centric network.

2. Key Technical Components:

1. Mobile Switching Center (MSC):

  • Control Plane Functions:
    • The MSC plays a crucial role in SRVCC by handling the control plane functions related to call setup, handover decision-making, and signaling.

2. IMS (IP Multimedia Subsystem):

  • VoLTE (Voice over LTE):
    • SRVCC often works in conjunction with VoLTE. IMS provides the infrastructure for delivering voice services over LTE networks.
  • Media Handling:
    • IMS manages the media components of the voice call, ensuring that audio is properly encoded, transmitted, and decoded during handovers.

3. eNB (eNodeB):

  • LTE Base Station:
    • The eNB, or LTE base station, is responsible for managing the radio interface and signaling in the LTE network.
  • SRVCC Handover Decision:
    • The eNB is involved in the decision-making process for initiating an SRVCC handover, considering factors such as signal strength and network conditions.

4. MSC Server:

  • Handover Signaling:
    • The MSC Server manages the signaling involved in handing over the voice call between LTE and legacy circuit-switched networks.
  • Interworking Functions:
    • It ensures proper interworking between the LTE network and the circuit-switched network during the handover.

5. Circuit-Switched Network (2G/3G):

  • CS Core Network:
    • The CS core network, associated with 2G or 3G technologies, handles the voice call when the handover occurs.
  • Legacy Circuit-Switched Infrastructure:
    • The SRVCC handover ensures a seamless transition to the legacy circuit-switched infrastructure, allowing the voice call to continue without interruption.

3. SRVCC Operation:

1. Triggering the Handover:

  • Coverage Area Change:
    • SRVCC handover may be triggered when a user moves out of the coverage area of the LTE network and needs to be handed over to a 2G or 3G network.
  • Signal Strength Criteria:
    • The decision to trigger an SRVCC handover is often based on factors such as the signal strength of the LTE network falling below a certain threshold.

2. Handover Process:

  • Preparation Phase:
    • Before the handover, preparations are made, including notifying the IMS, allocating resources, and ensuring the compatibility of the target circuit-switched network.
  • Handover Execution:
    • The actual handover involves signaling between the LTE and circuit-switched networks to seamlessly transfer the voice call.

3. Post-Handover Optimization:

  • Quality Checks:
    • After the handover, quality checks are performed to ensure that the voice call maintains acceptable levels of quality in the circuit-switched network.
  • Resource Release:
    • Resources allocated in the LTE network for the voice call are released once the handover is successful.

4. Challenges and Considerations:

  • Interworking Challenges:
    • Ensuring smooth interworking between LTE and circuit-switched networks can be complex and requires careful coordination.
  • Voice Codec Compatibility:
    • Compatibility between voice codecs used in LTE and legacy networks must be considered to avoid degradation of voice quality.

Conclusion:

Single Radio Voice Call Continuity (SRVCC) is a critical technology that ensures a seamless transition of voice calls between LTE (PS domain) and legacy circuit-switched networks (CS domain). This capability is essential for providing users with consistent voice communication experiences, especially when moving between different coverage areas served by diverse network technologies. The technical components and operations involved in SRVCC highlight the complexity and sophistication required to maintain voice call continuity across evolving telecommunication standards.