Voice over LTE (VoLTE) generates a lot of hate among IP communications pundits. A recent Twitter exchange I had around VoLTE verses OTT quickly degenerated into a one-sided rant from the other party listing different ways VoLTE could go wrong when trying to make a phone call. I'm no big fan of VoLTE, but there is a near-messianic hate of the technology.   I'd like to see people grow up a bit when they discuss it, rather than devolving into a knee jerk rant about the evils of the old style phone world.

Let me start with three basic premises:  1) Like it or not, VoLTE is the future of telco voice.  2) VoLTE isn't perfect, but neither is OTT, and 3) VoLTE is built with quality of service in mind from top to bottom, not dependent upon best-effort IP over a dumb pipe.

IP communications purists will point out that VoLTE is arguably just an OTT application riding on top of the LTE IP network.   It was designed in a GSMA committee and codified as a standard without input from Internet people or other free thinkers.  Additionally, it uses a voice encoding scheme—AMR-WB—that happens to be proprietary and requires licensing fees.

All of that's true, but VoLTE is an application designed to take advantage of LTE's ability to deliver Quality of Service (QoS) to applications. It is also designed, with some silicon and backend refinements, to seamlessly transfer calls from VoLTE networks onto previous generation GSM/WCDMA networks.  VoLTE also has power optimization principles built into how it works with the radio network that make it more energy efficient than always-pinging OTT services. 

For better or worse, VoLTE is also tied in with IMS to deliver some of its features and mentioning IMS to IP communications purists just gets them foaming at the mouth more for being too complex and too expensive, a "telco" solution.  Yet IMS continues puttering along in large phone companies as the world migrates off the PSTN and onto IP-based voice networks.  

The current generation of over-the-top voice apps don't have access to QoS offered by IMS and LTE.  To get access to QoS would require an agreement with the network operator and the appropriate back-end support.  At CTIA a few years ago, Ericsson was shopping around a solution to provide priority QoS for gaming applications, so it is possible other third-party applications could purchase QoS access on a wireless network if the monetary incentives were available.

OTT services run on the premise of "free," making money on either a per-minute or—more common these days—a flat monthly rate to dial out to the PSTN.   It remains to be seen if OTT and wireless services can find a balance point between themselves where an OTT would pay up for guaranteed quality of service.   The problem is an OTT would have to negotiate QoS arrangements across multiple carriers in order to gain some sort of advantage over other OTT players, assuming wireless service providers were able to go along.  It would be a formidable task and not one any traditional carrier has shown an interest in, even before the whole "pay lane/Net Neutrality" discussion kicks into high gear.

Ranting pundits would argue you don't need guaranteed QoS and the other engineered features of VoLTE are superfluous against the freedom of picking an OTT client.  I believe there's no clear winner and there might be some pushback against OTT, as there has been in the quality of generic cellular calls.  If VoLTE is successful at raising the bar of expectations on call quality and fewer dropped calls, OTT may have to step up its game down the road. But, VoLTE first has to get deployed and loaded before we can understand what businesses and consumers really want.