AT&T, Verizon Target VoLTE Interop in 2015, RCS Later


AT&T and Verizon have officially declared they are working on Voice over LTE (VoLTE) connections between their respective networks and customers.   VoLTE calls between Verizon and AT&T customers "is expected" in 2015, according to a statement from the companies.  And, there's also some Rich Communications Services (RCS) news buried in the text.

The announcement comes as three out of four major U.S. carriers promote LTE networks and a number of countries plan to turn up LTE and VoLTE in the next 15 months.  "Interoperability among VoLTE service providers in the United States and around the world will create a better and richer mobile experience for customers," declares Verizon's press release.

Engineers are working through a full set of requirements, starting with lab environments and moving to field trials.  Verizon points out that the works "lays the foundation for interoperability of other Rich Communications Services (RCS) such as video calls, rich messaging and more in the future."

I'm sure Dean Bubley—big WebRTC analyst and not a RCS or VoLTE fan—is screaming loudly if he caught the mention.  Color me annoyed, because the marketing people are once again using VoLTE as the dumbed down code phrase for "It makes the network better," rather than discussing the details of IMS, peering, SIP peering, IP exchange (IPX) and RCS in detail.

Verizon's "Advanced Calling 1.0" offers VoLTE HD voice calling and video calling, but Verizon didn't say anything about RCS in its rollout of the service.  RCS under GSMA's joyn brand has been slowly picking up steam in Europe, but aside from fizzled launch attempts by MetroPCS (now T-Mobile US) and Sprint, there's been no mention or progress of RCS. 

The other kicker to Advanced Calling 1.0 is it appears to use RCS, but doesn't support the baseline RCS bits of IM, presence or file/screen sharing.  Maybe this will be addressed in Advanced Calling 1.5 or 2.0 or some other marketing-speak rollout in the future.

Snubbed in yesterday's announcement was the other carrier—I should say UnCarrier—running VoLTE nationwide, T-Mobile US.   T-Mobile has a wider VoLTE network footprint than AT&T and has been running it longer than Verizon. AT&T's CTO said "We continue to work with others in the industry on similar collaborative arrangements and hope to see similar collaboration across the industry in the near future."  T-Mobile is the obvious one to include in the short term.

AT&T has been working on Tier 1 SIP peering for quite a while, dating back a number of years.  From a network perspective, moving VoLTE calls to Verizon and vice versa is simply a matter of making sure their respective LTE networks have permissions to move IP and SIP sessions over a tested peering connection.

The news release didn't address transcoding between AMR-WB, VoLTE's native HD voice codec, and G.722, the broadband and business world's HD voice codec.  Enterprise customers are going to want HD voice quality on conference calls—if they aren't already yelling for it behind the scenes. Deutsche Telekom announced it is delivering HD voice transcoding on its networks between wireless and broadband customers, so it isn't an unreasonable technical or business problem.  Both AT&T and Verizon may not be in a hurry to do HD voice transcoding because neither offers G.722 outside of enterprise services.  We'll have to wait and see.

Edited by Maurice Nagle

Contributing Editor

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