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SR-VCC Single Radio Voice Call Continuity

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SR-VCC (Single Radio Voice Call Continuity) is a feature in cellular networks that enables seamless handover of voice calls between circuit-switched (CS) and packet-switched (PS) domains. It ensures uninterrupted voice communication when a user moves between different network technologies or coverage areas, such as 2G/3G to 4G/5G, or between Wi-Fi and cellular networks.

Here's a detailed explanation of SR-VCC:

  1. CS and PS Domains: In cellular networks, voice calls are traditionally carried over the circuit-switched (CS) domain, where a dedicated channel is established for the call duration. On the other hand, data services, including voice over IP (VoIP) calls, are transmitted over the packet-switched (PS) domain, which utilizes IP-based packet data networks.
  2. Handover Challenges: When a user on a voice call moves from a CS domain to a PS domain or vice versa, a seamless handover is required to maintain the ongoing voice call. The transition between different network technologies and domains can introduce disruptions or call drops if not properly managed.
  3. SR-VCC Functionality: SR-VCC enables the transfer of an ongoing voice call from the CS domain to the PS domain or vice versa without interrupting the call. It allows voice calls to continue smoothly during handovers between different network technologies, network types, or coverage areas.
  4. Media and Control Plane Separation: SR-VCC involves the separation of the media plane and control plane. The media plane carries the voice traffic, while the control plane manages call control signaling and negotiation between the CS and PS domains.
  5. CS-to-PS Handover: When a user moves from the CS to the PS domain, SR-VCC ensures a smooth handover. The ongoing voice call is transferred from the CS domain to the PS domain, and the voice media stream is seamlessly switched from the CS-specific channel to a PS-based VoIP channel. The call control signaling is maintained, allowing the call to continue uninterrupted.
  6. PS-to-CS Handover: In the case of a PS-to-CS handover, SR-VCC facilitates the transfer of an ongoing VoIP call from the PS domain to the CS domain. The voice media stream is switched from the PS-based VoIP channel to a CS-specific channel, while call control signaling is maintained to ensure the continuity of the call.
  7. Interworking with IMS: SR-VCC is often implemented in conjunction with the IP Multimedia Subsystem (IMS) architecture, which enables the delivery of voice and multimedia services over IP networks. SR-VCC leverages IMS capabilities to manage the interworking between the CS and PS domains, ensuring seamless handovers and call continuity.
  8. Quality and Codec Considerations: During SR-VCC handovers, there may be differences in voice quality and codec support between the CS and PS domains. SR-VCC implementations aim to minimize any degradation in voice quality and adapt to different codec requirements for seamless handovers.
  9. Network Support and Interoperability: SR-VCC requires support from both the network infrastructure and the user equipment (UE). Network elements, such as the mobile switching center (MSC), IMS core, and radio access network (RAN), need to be SR-VCC compatible. Similarly, UEs should support SR-VCC to ensure proper handover and call continuity.

SR-VCC plays a vital role in ensuring uninterrupted voice communication during handovers between different network technologies or coverage areas. By seamlessly transferring ongoing voice calls between the CS and PS domains, SR-VCC enhances the user experience, reduces call drops, and enables the utilization of advanced IP-based services while preserving voice service reliability.