What is SR-VCC Single Radio Voice Call Continuity

Unveiling SR-VCC: Ensuring Seamless Voice Calls in Evolving Networks

In the ever-evolving world of mobile communication, Single Radio Voice Call Continuity (SRVCC) plays a pivotal role in guaranteeing uninterrupted voice calls during network handovers. It empowers users to seamlessly transition between Voice over LTE (VoLTE) and legacy 2G/3G networks, maintaining call connectivity even when LTE coverage becomes unavailable.

Core Challenge: Maintaining Voice Continuity

• As mobile network operators (MNOs) roll out LTE and adopt VoLTE for voice services, ensuring uninterrupted voice calls during handovers becomes crucial.
• Legacy 2G/3G networks (GSM/UMTS) are still widely deployed, especially in remote areas or during network upgrades.
• The challenge lies in maintaining voice call continuity when a user transitions from an LTE coverage area (where VoLTE is used) to an area with only 2G/3G coverage.

How SR-VCC Works:

SRVCC acts as a bridge between VoLTE and legacy circuit-switched voice services. Here's a breakdown of the process:

1. Active VoLTE Call: A user initiates a voice call using VoLTE within an LTE coverage area. The call is established using an IP (Internet Protocol) Multimedia Subsystem (IMS) core network infrastructure.
2. Loss of LTE Coverage: As the user moves out of the LTE coverage area, the signal strength weakens.
3. SRVCC Trigger: The UE (User Equipment) detects a decline in LTE signal strength and triggers an SRVCC procedure.
4. Handover to Circuit-Switched Network: The IMS core network initiates a handover process. It instructs the UE to switch its voice call from the VoLTE session to a circuit-switched connection on the 2G/3G network (GSM/UMTS).
5. Call Continuity: The voice call seamlessly transitions from VoLTE to the circuit-switched network, and the user remains connected without any disruption.

Benefits of SRVCC:

• Uninterrupted Voice Calls: SRVCC ensures that ongoing voice calls are not dropped when transitioning between LTE and legacy networks, providing a smoother user experience.
• Efficient Network Utilization: By enabling handovers to 2G/3G networks for voice calls, MNOs can optimize their network resources by focusing LTE capacity on data traffic.
• Cost-Effectiveness: SRVCC avoids the need for extensive and expensive nationwide LTE rollouts, especially in areas with lower voice call traffic.

Technical Considerations:

• SRVCC requires support from both the UE and the network infrastructure. UEs need to be equipped with hardware and software capable of handling SRVCC handovers.
• The network needs to have the necessary functionalities within the IMS core and radio access networks (RAN) to facilitate SRVCC procedures.
• The handover process involves signaling procedures and coordination between the LTE network, the IMS core, and the 2G/3G network to ensure a smooth transition.

Comparison with CSFB (Circuit Switched FallBack):

• Another handover technique, Circuit Switched FallBack (CSFB), also allows users to fall back to 2G/3G networks for voice calls when LTE coverage weakens.
• However, CSFB operates at the device level without IMS core network involvement. While simpler, CSFB might not offer the same level of control and handover optimization compared to SRVCC.

Limitations of SR-VCC:

• Latency: The handover process might introduce a slight delay in the call, although this is usually imperceptible to users.
• Network Dependence: SRVCC relies on the availability and quality of the 2G/3G network for seamless handover.
• Legacy Technology Dependence: As 2G/3G networks are gradually phased out, the long-term viability of SRVCC might be limited.

Future of SR-VCC:

• With the ongoing rollout of 5G New Radio (NR) networks, the role of SR-VCC might diminish as 5G NR is designed to support Voice over New Radio (VoNR) services, potentially offering wider coverage and improved voice quality.
• However, SR-VCC is expected to remain relevant in the near future, ensuring voice call continuity during handovers between LTE and legacy networks for a significant portion of mobile users globally.

Conclusion:

SRVCC plays a crucial role in maintaining seamless voice call continuity during network handovers within mobile communication systems. By enabling transitions between VoLTE and legacy 2G/3G networks, SRVCC ensures uninterrupted voice calls for users, even when LTE coverage is limited. However, the evolving network landscape with the emergence of 5G NR might eventually lead to a diminished reliance on SR-VCC as VoNR services gain traction.