What is CSFB and SRVCC in LTE?

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What is CSFB and SRVCC in LTE?

CSFB (Circuit Switched Fallback) and SRVCC (Single Radio Voice Call Continuity) are two mechanisms used in LTE (Long-Term Evolution) networks to ensure seamless voice services during transition scenarios between LTE and legacy circuit-switched networks. Let's explore each of them in detail:

CSFB (Circuit Switched Fallback):

CSFB stands for Circuit Switched Fallback. It is a mechanism that allows a mobile device to continue a voice call while being handed over from an LTE network to a 2G or 3G network.

When a mobile device is making a voice call over LTE, it is connected to the LTE network using a packet-switched (PS) connection. A PS connection is a connection that is used to carry data, such as voice calls, text messages, and data transfers.

When the mobile device moves out of range of the LTE network, it will be handed over to a 2G or 3G network. This is because 2G and 3G networks use circuit-switched (CS) connections to carry voice calls. CS connections are more reliable than PS connections, and they are less likely to be dropped during a handover.

During a CSFB handover, the mobile device will temporarily disconnect from the LTE network and connect to the 2G or 3G network. The voice call will then be transferred to the 2G or 3G network. Once the mobile device has connected to the 2G or 3G network, the voice call will be resumed.

• CSFB is a mechanism that allows LTE-capable devices to fallback to legacy circuit-switched networks (2G or 3G) for voice calls.
• In LTE networks, voice calls are typically carried over the IP-based LTE network using VoLTE (Voice over LTE) technology. However, if an LTE device needs to make or receive a voice call, and there is no VoLTE coverage or the device doesn't support VoLTE, CSFB is triggered.
• During CSFB, the LTE device temporarily leaves the LTE network and accesses the legacy circuit-switched network (2G or 3G) to establish the voice call. The device switches its radio connection to the legacy network for the duration of the call.
• After the voice call ends, the device returns to the LTE network for data services, as LTE provides faster data speeds and better network capacity.

SRVCC (Single Radio Voice Call Continuity):

SRVCC stands for Single Radio Voice Call Continuity. It is a mechanism that allows a mobile device to continue a voice call while being handed over from an LTE network to another LTE network.

When a mobile device is making a voice call over LTE, it is connected to the LTE network using a PS connection. A PS connection is a connection that is used to carry data, such as voice calls, text messages, and data transfers.

When the mobile device moves out of range of the current LTE network, it will be handed over to another LTE network. This is because LTE networks are designed to seamlessly hand over mobile devices from one network to another.

During an SRVCC handover, the mobile device will not be disconnected from the LTE network. Instead, the voice call will be transferred to the new LTE network. Once the mobile device has connected to the new LTE network, the voice call will be resumed.

• SRVCC is a mechanism introduced in LTE networks to provide uninterrupted voice services when transitioning between LTE and legacy circuit-switched networks.
• SRVCC enables the handover of an ongoing voice call from the LTE network (VoLTE) to the legacy circuit-switched network (2G or 3G) without interrupting the call.
• When an LTE device initiates a voice call over VoLTE, the call remains on the LTE network as long as possible. However, if the LTE signal weakens or the device moves out of LTE coverage, SRVCC is triggered.
• During SRVCC, the LTE device performs a seamless handover from VoLTE to the circuit-switched network, ensuring that the voice call continues without interruption. The handover is coordinated between the LTE and circuit-switched networks to maintain call quality and reliability.
• When the LTE device returns to LTE coverage, it can switch back to VoLTE, and the ongoing call is handed back to the LTE network, ensuring a smooth transition between the networks.

Both CSFB and SRVCC mechanisms are important for providing voice services in LTE networks, especially in scenarios where VoLTE coverage is limited, or the device lacks VoLTE support. CSFB allows devices to fallback to legacy circuit-switched networks for voice calls, while SRVCC enables seamless handover between VoLTE and circuit-switched networks during ongoing voice calls, ensuring uninterrupted communication for LTE users.

Benefits of CSFB and SRVCC

Here are some of the benefits of using CSFB and SRVCC:

• They allow mobile devices to continue voice calls even when they move out of range of the LTE network.
• They reduce the number of dropped calls.
• They improve the quality of voice calls.

Challenges of using CSFB and SRVCC

Here are some of the challenges of using CSFB and SRVCC:

• They can cause a short interruption in the voice call during the handover process.
• They can require more network resources than a traditional voice call.
• They can be more complex to implement and manage than a traditional voice call.