Circuit Switched Fallback Falls Short

One of the hottest topics right now in Telecoms is Voice over LTE, or VoLTE as it’s more commonly known. This technology will enable Mobile Service Providers (MSPs) to finally deliver voice calls across their entire IP, access and core network. This capability will help create a more efficient end-end network infrastructure, and also take advantage of the policy rules now available to ensure optimum customer call Quality of Service (QoS).

Read: Give VoLTE a Voice

But despite the benefits for an MSP in implementing VoLTE, to date, rollout of the technology has been slow. The cause for this lies in a number of reasons, with one of the most significant being the availability of an alternative approach to delivering voice services: Circuit Switched Fallback (CSFB).

Why Circuit Switched Fallback May Not Be the Answer

The theory behind CSFB is simple. The LTE device essentially registers and connects to the LTE network, enabling the customer to utilise the high bandwidth and high speed packet network for all data-related services. However, when it comes to either making or receiving calls, the device then “falls back” to the legacy circuit switched 2G/3G network. Sounds simple, but in practice, implementation has uncovered a number of challenges for MSPs.

When a device performs the fallback procedure, initial tests have shown that it can take 3-6 seconds longer for a call to be set up. This delay exposes what in actual fact is a complex procedure, which involves successful initiation of the legacy radio network, including channel measurements, in order to determine the correct cell and frequency for the associated device. Such a delay in call setup of course results in a poor experience for the customer.

For outgoing calls that experience this kind of delay, the customer may actually think the call cannot been completed and so decide to hang up. And the situation gets worse when a call is from an LTE device to an LTE device. In such a case, both devices must perform the fallback procedure, representing an even greater delay before the call is connected.

Customer Experience: The Deciding Factor

Clearly, while CSFB may well be an alternative, it is most likely only useful in the short-medium term. Ultimately, customer experience will be the deciding factor that will eventually drive MSPs to implement true Voice over LTE.

For more information about understanding customer experience in LTE deployments, read this paper. Do you have any thoughts about Circuit Switched Fallback vs VoLTE? Let me know in the comments below.

Written by Graham Kunz – Graham on Twitter | Posts by Graham
Graham is Empirix’s European Service Assurance Expert and he’s worked in the tech industry for nearly twenty years. More than 14 years of that time has been in Service Assurance, working with wireless customers and internal teams to understand and capture product requirements, as well as develop and introduce products. His global outlook, wireless technology knowledge and technical know-how provide him with an excellent perspective on the current and future direction of mobility and the wireless industry.

photo credit: dennisborn via photopin cc

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