Telefónica has become the first network operator to demonstrate the successful transfer of voice calls from an LTE network to a 3G mobile network. The handover was achieved in Germany in a test laboratory environment, using the Voice over LTE (VoLTE) standard.

The subject of voice calls on LTE networks has at times been utterly perplexing and incredulous – a mobile network that doesn’t natively support voice? What on earth were they thinking? The problem first emerged at the Mobile World Congress event a few years ago and was meet with general disbelief, yet it was true. Two solutions soon emerged, VoLTE and VoLGA (Voice over LTE Generic Access). The latter was created more as an interim solution, due to the frustration in getting VoLTE working.

VoLTE now looks like the winning option, with the backing of the majority of the LTE community. The problem is that without it, LTE operators still need the legacy 3G or 2G networks to carry voice traffic, as LTE is data only. The solution therefore is to simply convert voice into data packets and squirt this over the data network – except it hasn’t proved that simple.

That was the first problem. The next problem involves the handover of calls that pass from the still limited LTE network coverage and onto the wider 2G or 3G network. As Telefónica correctly explains in its release accompanying its technology test, while there has been recent progress with VoLTE technology in South Korea and the US, today’s LTE networks are not able to handover a VoLTE voice call to 2G or 3G when moving out of LTE coverage. This means most networks fall back to legacy networks whenever they make or receive a voice call (using Circuit Switched Fallback, CSF), or as it is the case with South Korea stay within the LTE network.

Telefónica’s engineers in Germany have demonstrated the SRVCC standard (single radio voice call continuity) allows for the handover of a VoLTE call from the LTE network to 3G. Handsets and network components from over six different manufacturers have been used, including Acme Packet, Ericsson, Huawei, NSN, Qualcomm and Sony Mobile. Enrique Blanco, CTO of Telefónica, said of this landmark test:

“With VoLTE, our customers will be seamlessly connected to a superfast intelligent network that not only gives a top quality voice service – but also a network that opens up a new world of opportunities, such as high definition video calls.”

What’s needed now though are more LTE devices with software to support VoLTE, as these remain few and far between. But that’s not going to happen anytime soon – heck, there are even major vendors (hello Apple) who still don’t support IMS. In fact, neither is widespread rollout of VoLTE imminent – 2014 is the most optimistic date, but 2015 looks a better bet. Unless telcos other than Telefonica are happy to stick with CSF and hasten the demise of voice. So many uncertainties.

If you want some further technical insight into the issues of VoLTE and handover, Martin Sauter’s blog is a good place to start.