A Short Introduction to VoLTE

A few years ago, when it seemed apparent that all communications are moving to an IP based world, mobile operators had to decide on the standard to use in their all-IP world. SIP was selected for that purpose as the base protocol, with a lot of additional protocols taking part to comprise the whole network. The end result (which is an ongoing standardization effort) is IMS – the IP Multimedia Subsystem.
IMS was adopted by all other incumbent service providers – wireline, wireless and cable, which in a way made sure of continuity of service, interoperability and roaming between operators. Fun as it is, the problem with IMS is its complexity: it comes to replace a hundred years of developments in voice technologies, and wrap into their future network advanced services such as rich multimedia and presence.
And so it came to be that no operator to this date was capable of rolling out a full-fledged network in a commercial manner – at least not that I know of. There are a lot of IMS trials out there, but I don’t think any of them is really considerable enough to be treated as a valid service compared to what we’re used to in the good old circuit switched world.

So what do we have?

•    Complex technology – IMS
•    Carriers that have to replace their whole network – LTE, the 4G network has nothing but IP, so all voice communication over that network is pure IP
•    VoIP start ups breathing down the necks of service providers – promising to take their business

Enter One Voice

One Voice is a new initiative making its first major step today – getting adopted by the GSMA. Think of it as a narrowing of IMS to the bare minimum that a mobile service provider offers today to its customers (that would be voice and SMS). In a way, it translates the KISS (Keep It Simple and Stupid) principle to IMS – it simplifies IMS to a point in which operators can start implementing and experimenting with it on a real network with a real ecosystem of vendors with interoperable solutions.
In essence, One Voice started by a group of companies, and now it has found a home at the GSMA, where it has been renamed to VoLTE, with a mission to define end-to-end service principles for Voice over LTE.
Why was this simplification in order? That’s because SIP (and IMS) have multiple ways of implementing each and every service, which makes interoperability between vendors quite challenging. So when you narrow down the scope, and indicate what is the exact way to implement something – it makes it easier to follow.
So what exactly can we find in the VoLTE draft specification? What problems does it solve?
•    Indication of what is mandatory and what is optional out of IMS
•    Registration to the network, including authentication and signaling compression
•    Dialing out and accepting incoming voice calls
•    Sending and receiving SMS messages
•    Supplementary services to calls (identification of caller/callee, privacy of identification, call diversion, call barring, hold, message waiting and conference calls)
And that’s the initial draft. VoLTE is an ongoing effort that will grow with time, encompassing more services that will get deployed by service providers. While the VoLTE public draft isn’t available yet, it’s basis is the One Voice specification which is available online (PDF) – if you are dealing with VoIP, SIP, IMS or service provisioning, then you should probably take a look at it.

I’ve written in two other places about One Voice, before it became VoLTE – you might want to check them out as well:
•    The One Voice Initiative (No Jitter)
•    How Will Operators Kill Them Mobile VoIP Startups? (VoIP Survivor)