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VoLTE Part 1: What is VoLTE and How Does it Work?

Posted by Paul Desmond

Sep 25, 2014

There’s been significant buzz about VoLTE lately, or Voice over Long-Term Evolution, with all the major wireless carriers making announcements about their rollouts and making good on earlier promises, Verizon being the latest (at least as of this writing). VoIP_VoLTE_Call_Protocol

It seemed a good time, then, to explore just what VoLTE brings to the table, where we stand in terms of coverage and the effect it may have on the UC universe. To cover all that, I talked with Bill Welch, senior product manager for the signaling line at Sonus Networks, which makes session border controllers (SBCs) and other equipment that helps make VoLTE possible and safe to use.

VoLTE: What It Is and What It Does

VoLTE is all about enabling voice calls to travel over the IP-based data portion of a wireless carrier’s network. Traditionally, voice traveled over the circuit-based portion of the network, such as the CDMA network for carriers like Sprint and Verizon. Essentially, VoLTE is to carriers like voice-over-IP (VoIP) is to enterprise customers.

“We’ve had VoIP for a long time in enterprises and fixed networks, but VoIP on a mobile carrier network is brand new,” Welch says. Given that, carriers needed to devise a way to ensure voice calls would work properly over their data networks, much of it having to do with the tight timing constraints voice requires and LTE coverage. “It’s all about timing budgets and universal LTE coverage. If you fall outside the timing budget or LTE coverage and roam to 2G/3G the call may drop,” Welch says.

Ultimately, VoLTE was the scheme a group of carriers agreed to for how to accomplish the task. And that agreement is crucial if users are to be able to make and receive calls from one carrier’s network to another.

VoLTE also provides a fallback mechanism for instances when a call starts on an LTE network but the caller moves into an area where LTE isn’t supported. In that case, VoLTE provides a way to fall back to the older 2G/3G circuit-switched network without dropping the call, Welch says.  

Where VoLTE Stands: The Carrier and Equipment Picture

VoLTE is a big deal for carriers as it means they will no longer have to manage two separate networks, one for voice and one for data. Or, at least, that’s the end game; it’ll take a good long while to get there. Today, carriers are just getting their feet wet with VoLTE.

“Just about every operator I’m aware of has had their LTE network stood up for more than a year and are generally doing VoLTE trials,” Welch says. Verizon, for example, was doing a trial in the first half of 2014 and is now rolling out VoLTE service market by market.

The other side of the equation is the phone, which has to be VoLTE-capable. The iPhone 5 and 5s, for example, support LTE, but not VoLTE specifically; you’ll need the iPhone 6 for that. Probably that’s why so many people were sleeping out to get their hands on the  iPhone 6. (OK, maybe not. And there is some debate about whether the 5 could be tweaked to support VoLTE.)  

VoLTE-capable phones from other providers are also emerging, including the Samsung Galaxy S5 and LG G2, both of which Verizon has said it will support.

In a future post, we’ll go through some of the benefits of VoLTE as they apply to unified communications.



Topics: Voice, networking, Mobility, Wireless, Unified Communications,