What is CSFB and Srvcc in LTE?
Let me explain CSFB (Circuit Switched Fallback) and SRVCC (Single Radio Voice Call Continuity) in LTE, as these are essential technologies that enable seamless communication between LTE and legacy networks like 2G and 3G. If you’ve been following our previous articles, you might have noticed that LTE primarily focuses on data transmission. However, voice calls, which are critical for mobile users, still rely on older technologies. This is where CSFB and SRVCC come into play.
CSFB (Circuit Switched Fallback) is a mechanism that allows LTE users to make and receive voice calls, even though LTE itself does not support circuit-switched voice services. Since LTE uses IP-based packet-switched technology for data, voice calls cannot be directly made over LTE. CSFB solves this problem by falling back to the 2G or 3G network when a user initiates a voice call. This process is seamless, so the user doesn’t experience any disruption in service, but instead, their voice call is handled by the legacy network while their data continues over LTE.
How does CSFB work? When a user is on an LTE network and attempts to make or receive a voice call, the network temporarily hands over the call to a 2G or 3G network that supports circuit-switched calls. Once the call is finished, the user is switched back to LTE for data services. This allows operators to offer voice services even without a native LTE voice solution, ensuring that customers can still make calls while benefiting from the fast data speeds of LTE.
SRVCC (Single Radio Voice Call Continuity) is a more advanced feature that ensures voice call continuity when a user moves between different types of networks. This is particularly important when a user starts a voice call on 2G or 3G networks and then moves to an LTE network during the call. SRVCC allows the voice call to continue seamlessly without dropping, even though the user switches from a legacy circuit-switched network to a packet-switched LTE network.
In essence, SRVCC enables a voice call to be handed over from 2G/3G to LTE without interruption. It provides high-quality voice service (often using VoLTE in LTE networks), allowing the user to enjoy continuous service as they move across different network types. SRVCC is especially useful when users are in an area where LTE coverage is available, but the initial call was made on 2G/3G networks.
The key difference between CSFB and SRVCC is that CSFB only allows for a voice call to fall back to 2G or 3G for voice, while SRVCC ensures that the call remains continuous as the user moves across LTE and legacy networks. This seamless transition between networks improves the user experience, particularly when moving between different network generations, without any call drops.
In summary:
- CSFB: Allows voice calls to fall back to 2G/3G when on LTE, as LTE does not support circuit-switched voice.
- SRVCC: Enables voice call continuity when moving between different networks (from 2G/3G to LTE and vice versa) without dropping the call.
As we learned earlier in our discussions about LTE and its evolution, CSFB and SRVCC are vital for offering a seamless user experience, especially for users who need both voice and data services on their mobile devices. They ensure that voice calls are not interrupted, even when users switch between different network technologies. Without these mechanisms, users would face dropped calls and service disruptions when transitioning between LTE and legacy networks.