Verizon, AT&T, others rally on IMS approach to voice over LTE

Verizon Wireless, AT&T and several major international carriers and vendors threw their support behind an IMS-based approach to delivering voice and SMS services over LTE networks. The level of operator support--the approach also is supported by Orange, Telefonica, TeliaSonera and Vodafone--sits in sharp contrast to another approach, called Voice over LTE via Generic Access, or VoLGA, which is supported by T-Mobile International.

Vendors including Alcatel-Lucent, Ericsson, Nokia Siemens Networks, Nokia, Samsung Electronics and Sony Ericsson also voiced their support for the initiative, dubbed One Voice. The companies said they concluded that an IMS-based approach "is the most applicable approach to meeting the consumers' expectations for service quality, reliability and availability when moving from existing circuit-switched telephony services to IP-based LTE services. This approach will also open the path to service convergence, as IMS is able to simultaneously serve broadband wireline and LTE wireless networks."

The companies said that the purpose of the initiative is to create the largest LTE ecosystem possible, and to avoid fragmentation of technical solutions.

Interestingly, both Alcatel-Lucent and Ericsson also support the VoLGA approach, and Nokia Siemens has supported its own solution, called Fast Track Voice, which proposes having mobile switching center servers handle VoIP traffic over LTE networks. VoLGA proponents argue that their approach should be used as an interim solution. All three vendors said they do not see a conflict in supporting the different approaches.

"We have been supporting the IMS approach from the beginning," Nokia Siemens spokesman Kent Tankersley told FierceWireless. "We look at an all-IP-based architecture as the ultimate goal for LTE. The Fast Track is a way the intermediate step, a bridge to that IMS."

Ed Elkin, director of IMS marketing at Alcatel-Lucent, said the company supports One Voice, VoLGA and circuit-switch fallback approaches for delivering voice over LTE. However, he said that One Voice is attractive for several reasons. "Once Voice, by giving the handset the handset manufacturers a common target to aim at, increases the likelihood that they can create a variety of handsets for the subscriber to choose from," he said.

He said that VoLGA will continue, but noted the broad support for One Voice likely would increase the possibility of global roaming. "Other methods have a narrow operator base," he said.

Peter Linder, director for network solutions at Ericsson, said that the One Voice approach was a "lightweight collaboration model" aimed at accelerating market adoption of LTE.

"We felt that the industry was a little bit unclear about the timing for when voice over LTE would happen for 3GPP standards," he said. "If we could take that uncertainty out of the marketplace and create clarity," he said, that could help drive momentum in the LTE ecosystem.

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