Voice over LTE demos reveal merits of competing claims.

Backers of two competing specifications for delivering voice over LTE mobile data networks have  both been boosted by demonstrations in the past two days. However, mobile giant Ericsson has dropped its support for VoLGA, one of the two systems.

LTE (Long-Term Evolution) is shaping up as the choice of most mobile operators worldwide for next-generation networks, but it can't carry voice or SMS (Short Message Service) traffic in the same way today's carrier networks do, because it's a packet-based IP data network. Equipment vendors and carriers have been lining up around two approaches to handling voice on LTE, called VoLGA (Voice over LTE via Generic Access) and One Voice.

On Thursday, Nokia Siemens Networks said it had recently carried out a voice call over LTE networks at its research and development centers in Germany and Finland. The call used the company's Fast Track VoLTE technology, which it said is aligned with the One Voice initiative. Nokia Siemens joined heavy hitters including Alcatel-Lucent, Nokia, AT&T, Verizon Wireless and Orange in the announcement of One Voice last month.

The Fast Track system provides a call control technique that is fully standardised by the 3GPP (Third-generation Partnership Project), the governing body for 3G and LTE, according to Nokia Siemens. It takes advantage of IP Multimedia Subsystem (IMS), an emerging system for deploying wired and wireless services. The company also said that it would soon test voice calls with a fully implemented IMS platform.

Nokia Siemens' announcement came just a day after Deutsche Telekom announced it had completed an LTE voice call using VoLGA technology. It used independent VoLGA-based systems from Kineto Wireless and Alcatel-Lucent, the German carrier said. Yesterday, Kineto announced a new release of software for its access gateway that the company said supports the VoLGA Forum's specification.

Meanwhile, one member of the One Voice group apparently has dropped its support for VoLGA. Ericsson, a key former member of the VoLGA Forum, has quit the organization, according to news reports this week. The  VoLGA website, which used to list Ericsson as a member, no longer does.

"That's a pretty significant blow to VoLGA," said IDC analyst Godfrey Chua.

Ultimately, mobile operators with LTE are likely to carry voice and SMS traffic alongside data on a single network using LTE, which makes more efficient use of radio spectrum. But the transition to that point is likely to take several years, while voice keeps going over 3G and older networks, Chua said. LTE will first be used to offload data traffic from devices such as laptops, to free up capacity on 3G networks, he said. LTE handsets are not expected to arrive until after next year, and carriers expect to keep their 3G networks up for several years. Verizon said earlier this year its 3G network would keep operating for at least five to seven years.

"It's not make-or-break to have a voice solution right away," Chua said. However, carriers want to know what approach vendors plan to take so they don't get stranded with one they don't want when the time comes, he said.