Vendors: Verizon Wireless the exception in 2G-LTE VoIP integration

Verizon Wireless (NYSE:VZ, NYSE:VOD) may be keeping its VoIP and circuit-switched voice services separate, but that doesn’t mean other vendors will follow the same path as they move voice on to their long-term evolution (LTE) networks, according to vendors working on voice-over-LTE (VoLTE) deployments.

At last month’s Mobile World Congress, VZW announced it has completed its first successful VoLTE calls, putting it well ahead of any other operator and on track to launch the first carrier-class mobile VoIP service next year.

But Verizon also revealed it would be leaving out a major piece of the VoLTE puzzle: cross-network mobility, which would allow Verizon to hand over VoIP calls on LTE to its legacy CDMA network and vice versa. VZW chief technology officer said that Verizon plans to have such an extensive LTE footprint in 2012 that such handover capabilities would be largely unnecessary. By 2013, Verizon envisions offering LTE-only handsets in areas where its LTE network is near ubiquitous. To invest in the circuit-to-packet infrastructure necessary to bridge the two networks would thus be an expensive and unnecessary step, Melone said.

In short, Verizon is moving so aggressively with LTE and VoIP it can afford to skip a step in its network and service evolution that other operators still plan on taking, said Danny Locklear, Alcatel-Lucent (NYSE:ALU) senior director of LTE global marketing solutions.

Alcatel-Lucent is working with Verizon and several other operators on deploying VoLTE over an IP Multimedia Subsystem (IMS) architecture as part of the One Voice initiative. Most operators are migrating their networks gradually from circuit-switched to VoIP services, so bridging the legacy and LTE networks is still firmly in their plans, Locklear said. “Verizon is in a unique situation,” Locklear said. “It feels that it will have the LTE coverage so that this won’t be an issue.”

Even if Verizon wasn’t being so aggressive with LTE, it may have other reasons to avoid the integration of its two voice networks. As a CDMA operator, Verizon doesn’t have a standards-based path to deliver that kind of integration, said Natasha Tamaskar, vice president of product marketing at Genband.

GSM operators can lean on the 3GPP standards, which provide for a step-by-step migration from circuit to packet voice. CDMA’s standards body, the 3GPP2 provides plenty of guidelines for integrating the packet data cores of the CDMA and LTE networks, but not much in the way of circuit-to-packet migration (though the 3GPP2 is supposedly working on a standard). Verizon wouldn’t be able to support LTE-to-CDMA voice call hand-off even if it wanted to, Tamaskar said. “There is no option from a CDMA operator’s perspective,” she said.

More: The Four Steps to Voice over LTE