If you haven’t already, soon you’re going to be hearing a lot about a new standard for making mobile phone calls: VoLTE. It stands for “voice over LTE,” but what it really means is that before long, your voice calls are going to be transmitted across the airwaves using the same technology the Internet pioneered for data.
VoLTE, an acronym sure to be coming soon to a mobile-phone advertisement near you, promises two immediate potential benefits to consumers: clearer calls with fewer dropouts and the ability to use voice and data services simultaneously (which some, but not all, carriers offer already). For the carriers, it means more efficient use of their allocated radio spectrum, meaning they can serve more customers without additional network investments.
(What VoLTE almost certainly won’t do is lower your phone bill, as carriers have a habit of charging more for network improvements that actually save them money.)
To understand how VoLTE is supposed to manage all these improvements, you have to understand why traditional LTE couldn’t carry voice.
Circuit Switched Vs. Packet Switched
LTE is the current gold standard for mobile data (it stands for “long term evolution”), although you may know it better as “4G.” LTE makes it possible to download or stream Internet video far faster than its predecessor 3G networks—but as it stands, LTE doesn’t carry voice calls. Instead, carriers with LTE fall back to older 2G and 3G networks for calls.
Voice over LTE will change that.
LTE’s speed advantage stems from the way it handles data. 3G network standards like UMTS and CDMA basically open a dedicated channel between nodes to handle voice, text and data, a technique called “circuit switching.” This is a simple, but fairly expensive practice in network terms; it’s as if you got a dedicated lane for your morning commute that no one else could use. Great for you; terrible for everyone else.
See also: Meet The “Real” 4G
LTE, by contrast, is based on an Internet technology called packet switching. In such networks, a sender divides up any sort of data—email, Web pages, a Netflix stream—into small packets of equal size, each of which carries an “address label” bearing its ultimate destination. The sender tosses these packets onto the network, where they’re directed toward their destination at every juncture, or “node.” They ultimately all meet up at their destination, where they’re reassembled and delivered to the recipient.
This is a lot more like your actual morning commute, in which you have to share the road with everyone else heading somewhere. Like your commute, packet switching sounds a bit haphazard, and it can be—but it’s also a fantastically efficient, flexible and robust way of transmitting information. Until now, though, it wasn’t any use for mobile voice calls, which still require circuits (and circuit switching).
When LTE debuted in the U.S., carriers had to figure out how to make voice calls work while pushing out 4G smartphones to customers. Most carriers adopted a stopgap measure called “circuit-switch fallback” in which LTE handles all data connections, but phones call back to the 3G network when you make a call. VoLTE effectively obsoletes this hybrid technology.
VoIP vs. VoLTE
You might look at your smartphone and say, “Hey, I can already make voice calls over my data connection! I have Skype and Google Hangouts!” It is true, you can indeed make voice calls using your data connection with these apps, which are referred in the cellular industry as “over-the-top” (OTT) services because they supersede a carrier’s own voice and messaging services.
You may be using LTE to make voice calls with these apps, but you’re not using VoLTE. Services like Skype, Hangouts, WebEx or Fuze are what is called Voice Over Internet Protocol—VoIP. These services work on your 3G or 4G LTE devices because they use your data connection through the Internet, not the traditional voice network from the carriers.
As U.S. cellular carriers networks evolve, VoLTE will compete with more directly with OTT services like Skype.
Benefits Of VoLTE
T-Mobile is one of the first cellular carriers in the United States to institute VoLTE phone calls on a limited range of smartphones, starting in Seattle. In an announcement last week, T-Mobile chief technology officer Neville Ray described the technology behind the company’s VoLTE offering:
If you’re like me and love digging into the underlying science, here’s how it works. (If this doesn’t interest you, feel free to skip this bit.) VoLTE calls will be carried over IP [Internet protocol, or packet switching] on our LTE network instead of a circuit-switched path on our 4G HSPA+ network. This is advantageous because your phone stays on our wicked fast LTE network to make a call. The tricky bit in all this is the smooth mobility between our various radio layers. Enhanced Single Radio Voice Call Continuity (eSRVCC) is a new LTE Advanced function and we’re excited to be the first to deploy it in the U.S. All of this basically helps ensure that your capable phone won’t drop a call if you leave an LTE area and it switches to 4G HSPA+ or 2G coverage.
Technologies like Enhanced Single Radio Voice Call Continuity are fancy terms used to described the central tenet of VoLTE. For the first time, voice and data will be living together in harmony on the same radio layer, meaning that smartphones won’t need to displace back to 3G or a different spectrum frequency to handle both capabilities.
What this means is that, as LTE is expanded in the U.S., old 3G networks like CDMA or HSPA+ will wither away. Verizon said last year that it will begin phasing out its 3G network at the start of 2014 and other U.S. carriers are planning similar rollbacks. The future of voice and data in the U.S. is LTE (and future advancements, like LTE Advanced), and carriers see no need to maintain costly old infrastructure.
The cellular operators are just starting their marketing campaigns around the evolution of LTE. T-Mobile claims what it calls “HD Voice” (clear voice calls over cellular) and Verizon claims to be rolling out what it calls XLTE, which is basically just extra spectrum for its existing LTE network to operate. Sprint’s Spark network isn’t an advance of LTE either, just a new mode of how it aggregates its various spectrum and varieties of LTE (TD-LTE and FD-LTE) into a more efficient package than its previous 4G offerings.
Smartphone manufacturers will benefit by the ability to trim how many radio receivers they place in smartphones. Instead of needing to support disparate networks with a variety of chipsets, they can just rollout phones with chipsets directed at specific carrier spectrum requirements.
For consumers, the benefit is harder to see. VoLTE will fix the unwelcome problem of not being able to use voice and data on a phone at the same time for some carriers, and calls may be clearer and less prone to be dropped going forward. VoLTE is an important evolutionary step in mobile computing, but it’s still possible that many consumers will hardly notice the change.