Understanding Voice Call Continuity in Modern Networks

Voice call continuity is a game-changer for modern networks. It ensures seamless communication between different networks and devices, even when users switch between Wi-Fi and cellular connections.

This technology is particularly useful in public areas where Wi-Fi is readily available. For instance, in a coffee shop, a user can make a voice call on their smartphone and the call will automatically switch to the cellular network if they move outside the Wi-Fi coverage area.

The key to voice call continuity is the use of advanced network technologies such as Voice over LTE (VoLTE) and Wi-Fi Calling. These technologies enable voice calls to be routed over the internet, rather than traditional cellular networks.

VoLTE, for example, allows voice calls to be made over 4G LTE networks, providing higher quality voice calls and faster call setup times.

Worth a look: Wi-Fi Calling

SRVCC, or Single Radio Voice Call Continuity, is a solution that transfers VoLTE calls in progress from LTE to legacy voice networks, while maintaining the QoS requirements. This ensures voice call continuity, which is critical for emergency calls.

Check this out: Why Business Continuity Plan Is Important

SRVCC works by enabling the transfer of calls in both directions from 4G to 2G/3G and 2G/3G to 4G. The handover process happens in two steps: Inter RAT Handover and Session transfer.

Here's a breakdown of the SRVCC handover process:

SRVCC supports both Packet Switching (PS) and Circuit Switching (CS), allowing for seamless voice call continuity.

Voice call continuity is a crucial aspect of ensuring seamless communication between callers and organizations. SRVCC (Single Radio Voice Call Continuity) solution transfers VoLTE calls in progress from LTE to legacy voice networks, while maintaining the QoS requirements.

This means that voice calls can be transferred smoothly even when there are gaps or weaknesses in LTE coverage. Without SRVCC, operators with such gaps or weaknesses cannot realize the user experience and network efficiency.

SRVCC supports both Packet Switching (PS) and Circuit Switching (CS), making it a versatile solution for various network environments.

Readers also liked: Why Is Continuity Important

By ensuring voice call continuity, operators can accelerate time to market and realize benefits during the entire time span from today's hybrid network environments.

Here are some key benefits of SRVCC:

Network architecture and standards play a crucial role in ensuring voice call continuity. The GSMA has provided guidelines for SRVCC to ensure interoperability with legacy networks.

Starting from 3GPP Release 8, SRVCC has evolved continuously to improve handover performance. The GSMA recommends using 3GPP Release 10 architecture for SRVCC, which reduces both voice interruption delay and dropped call rate compared to earlier configurations.

The Release 10 configuration includes all necessary components to manage time-critical signaling between the user's device and the network, and between network elements within the serving network. This ensures that signaling follows the shortest possible path and is as robust as possible, minimizing voice interruption time caused by switching from the PS core to the CS core.

You might like: Software Communications Architecture

SRVCC Network Architecture is a critical component of modern network infrastructure. It ensures seamless handovers between different network types, maintaining voice continuity.

Starting from 3GPP Release 8, SRVCC has evolved continuously, driven by the need for interoperability with legacy networks. The GSMA has provided guidelines for SRVCC, detailing requirements for both networks and user devices.

SRVCC provides continuity for PS to CS handover between LTE and WCDMA/GSM networks and from LTE to CDMA networks. GSMA guidelines recommend 3GPP Release 10 architecture for SRVCC, which reduces voice interruption delay and dropped call rate compared to earlier configurations.

The network controls and guides the user device from LTE to 2G/3G as the user moves out of LTE coverage. The SRVCC handover mechanism is fully network controlled, with calls remaining under the control of the IMS core network.

The Release 10 configuration includes all components needed to manage time-critical signaling between the user's device and the network. This ensures that signaling follows the shortest possible path and is as robust as possible.

As a result, voice interruption time caused by switching from the PS core to the CS core is minimized, whether the user's device is in its home network or roaming.

For more insights, see: Media-independent Handover

Service standardization has been a crucial aspect of network architecture, with significant progress made in recent years. The Internet Engineering Task Force (IETF) has been at the forefront of standardization efforts, developing protocols such as TCP/IP and HTTP.

The widespread adoption of TCP/IP has enabled seamless communication across different networks, making it a cornerstone of modern networking. With over 90% of the world's networks using TCP/IP, standardization has become a reality.

The IETF's open standards process has ensured that protocols are developed in a collaborative and transparent manner, allowing for input from a diverse range of stakeholders. This has led to the development of robust and reliable protocols that are widely adopted.

In addition to the IETF, other organizations such as the International Organization for Standardization (ISO) and the Institute of Electrical and Electronics Engineers (IEEE) have also played a significant role in standardization efforts. Their contributions have helped shape the modern network architecture.

Curious to learn more? Check out: Call Center Ip Phone

Single Radio CSFB vs SRVCC is a crucial aspect of network architecture, particularly in the context of LTE networks. CSFB is a process that allows a user equipment to switch from LTE to a 2G or 3G network for voice calls.

CSFB requires the user equipment to perform a radio access bearer (RAB) setup on the target 2G or 3G network, which can lead to increased latency and poor user experience. This process is often seen as inefficient.

SRVCC, on the other hand, allows for a seamless handover from LTE to a 2G or 3G network for voice calls, minimizing the impact on the user experience. This is achieved through a process called IMS (IP Multimedia Subsystem) based SRVCC.

SRVCC is considered a more efficient and user-friendly solution compared to CSFB. It allows for a faster handover and reduces the likelihood of call drops.

A fresh viewpoint: Voice over LTE

In a voice call continuity scenario, poor internet connectivity can cause dropped calls and lost conversations.

Discover more: Node B

As we saw in the example of Sarah's dropped call, Wi-Fi and cellular network handovers can be notoriously unreliable.

Dropped calls can be especially frustrating when you're in a meeting or on a deadline.

The solution to this problem lies in the use of technologies like Voice over LTE (VoLTE), which can provide seamless handovers between networks.

However, even with VoLTE, dropped calls can still occur due to network congestion.

This can be mitigated by implementing call continuity solutions that automatically switch the call to a different network or device.

For instance, a call can be seamlessly transferred from a smartphone to a tablet or computer, ensuring that the conversation is never interrupted.

In addition, some solutions can even detect and adapt to changes in network conditions in real-time.

SRVCC Interruption Performance is a key issue with VoLTE and SRVCC, where the interruption time when handing over from an LTE RAN to a legacy RAN can be a problem.

The key technique behind reducing the time is to simultaneously perform the IRAT Handover and session transfer, which maintains the user experience and keeps the actual interruption time from being noticeable.

SRVCC Success Rate (%) measures the percentage of calls successfully transferred with SRVCC from LTE to 2G/3G Network, including both CS and PS call transfers.

A Call Drop rate (%) of less than 1% is the requirement for this metric.

Here are the key SRVCC KPIs in a concise list:

Voice call continuity is a feature that allows seamless transitions between different communication domains, such as circuit switched voice calls and IMS multimedia telephony sessions. This is achieved through a process called domain transfer.

The VCC Application Server (VCC-AS) plays a crucial role in this process, as it anchors calls that can be subject to domain transfer. This means that all CS calls that can be subject to domain transfer need to be interworked into IMS.

Tobias's experience with calling his sister Theresa illustrates this point. He dials her number, and during the routing of the call, the CS domain of his network becomes aware that the call can be subject to VCC domain transfer. The call is then interworked at the MGCF into Tobias's IMS domain.

Here are some call continuity features that can be useful in various situations: