With VoLTE implemented commercially in four networks globally – three in Korea and in MetroPCS in the USA – Warren said that there is still uncertainty within some operators about what exactly is required to get VoLTE to market. However, he added that there is top-level support for VoLTE within operators. “If you talk to operators at board level they will tell you they are going to do VoLTE at some point in the future: the timeline to get there varies,” he said.
“VoLTE is not happening as quickly [as we thought], and part of the reason for that is that there is a perceived complexity. Perhaps that’s partly because we haven’t done a good enough job of explaining how easy it could be, so we are going to define VoLTE in an end to end implementation guide that will outline the specifications with hooks into what you need to define it.”
The “how to” guide will not recommend any architecture over another, Warren said, with the GSMA keen not be seen as a “king maker”. Instead it can clearly outline the pros and cos of the different approaches, which stem from traditional core IMS elements from the main NEPs, to “IMS in a box” type solutions that integrate IMS functions into one platform, hosted solutions, to the SBC-defined approach of the likes of Acme Packet and Genband.
What’s important for the GSMA is that operators deploy VoLTE so that interconnect and interoperability between services can be support. “Interconnect is the major one, so for instance you make sure the same QoS classes are supported where the traffic meets. You need to do it the same way,” Warren said.
Warren said that another reason for the pushing back of VoLTE has been the provisioning of CSFB to support voice in early LTE networks.
“A lot of operators have done CSFB as an interim solution. I still hold the opinion I held three years ago that CSFB is something that really ought to be squeezed as far as possible. It’s not that it’s a bad technology in its own right; it gets you to the point where you have voice capability with LTE so you can launch LTE-capable smart phones. But the problem with CSFB is that it is a device and network implementation. So if you launch it and then you want to go to VoLTE you invest twice, you have to continue to support it whilst you’re rolling VOLTE out as well, and consumers have to invest twice. The likelihood now is that CSFB will have a longer life in the market,” Warren concluded.
“We are demonstrating the most advanced voice over 4G tests ever conducted”
Telefonica’s pure VoLTE
One operator demoing VoLTE at Mobile World Congress 2013 was Telefonica – in a demonstration it termed “pure VoLTE”. The carrier was showing WiFi to LTE handover for a voice call using the ANDSF protocol, supported by Ericsson, as the underlying control technology. ANDSF (Automatic Network Discovery and Selection Function) is a protocol that enables operators to extend control to WiFi endpoints as part of their overall network network policies. It is being included by many of the vendors that provide carrier WiFi equipment – and also requires client support on the device.
Enrique Blanco, CTO of Telefonica, said: “We are demonstrating the most advanced voice over 4G tests ever conducted, and additionally LTE data, with a clear focus on capacity, quality and speed.”
One thing ANDSF can do is support a connection to a WiFi access point according to operator policies. That means an operator could define, perhaps according to QoS rules, which access technology a device could be connected to – either as a function of access conditions or of the application itself. It can also offer control over a session (IP flows) so that the operator can offer voice handover, supporting VoWLAN in the same way as VoIMS. For call continuity when customers move from LTE to non LTE coverage areas, VoLTE uses a single radio solution in the customer’s device (SRVCC) that maintains the voice connection. That requires chipset support from the likes of Qualcomm for VoLTE/SRVCC capabilities.