The IMS One Voice Profile – Some Thoughts

There we go, lots of people have asked me in the past few days about my opinion on the publication of the IMS One Voice Profile to bring voice services to LTE. The spec, created by AT&T, Orange, Telefonica, TeliaSonera, Verizon, Vodafone, Alcatel-Lucent, Ericsson, Nokia Siemens Networks, Samsung and Sony Ericsson is available here.

There's a strong political and a technical side to this, so let's look at them separately.

The Politics

One of the main problems is that there is no clear strategy of how to deliver voice over LTE, the main cash cow of mobile network operators. As a result, several solutions have been suggested and specified, each with advantages and drawbacks.

As the impressive list of supporters shows, many parties hope and believe that the IP Multimedia Subsystem will do the job. Unfortunately, the IMS is suffering from its own complexity and the ambition of the companies working on it to evolve pure voice to a multimedia offering. Due to the complexity, however, little to nothing has so far ended up in the hands of consumers. The industry has tried to narrow their focus a bit by specifying service profiles such as MMTel and Rich Communication Suite version 1 and version 2 but there are no indications that this has changed this situation.

With the IMS One Voice Profile, many of the IMS supporters have now agreed to throw even more of the complexity overboard and concentrate on voice only. And that's the astonishing political side of this document to me. No longer are the companies dreaming their multimedia dream, they seem to have come to realize that they need to focus on voice and make this work first. An impossible suggestion only a short time ago. But the pressure seems to be mounting.

The Technical Side

When looking at the spec it seems to be likely that most IMS infrastructure vendors can already do the signaling exchanges described in the document and client software for mobile devices should also be complying either already or shortly. So from a technical point of view this spec doesn't change the status quo a great deal. Integrating this into a final solution is going to be the first tricky thing where the industry has failed over many years. Unfortunately the spec doesn't help with this issue.

The second tricky thing is the handover to a 2G or 3G circuit switched channel once running out of LTE coverage. Two features are required for this. The first is Single Radio Voice Call Continuity, a mostly radio network centric feature to coordinate the handover process from packet to circuit with devices that can only communicate with one radio access technology at a time. In addition, the IMS needs to interact with the circuit switched Mobile Switching Center (MSC). Although not mentioned in the 'One Voice' profile, I assume the IMS Centralized Services feature is used for that. If you want to see something really complicated, go have a look.

Some might argue that handovers to a CS channel are not required at first but I think without it, users will simply not accept the service as it offers few benefits over VoIP services offered by Internet companies. In fact, I think handover to CS is the biggest asset operators have to compete with Internet companies in the voice domain!

Final Thoughts

Personally, I think it's a good idea to concentrate IMS implementation activities on the most important service, VOICE! I have to wonder a bit, however, why to go through all this complexity for voice only, as that can be had for LTE much cheaper, much simpler and likely also much faster with other approaches such as Volga. Many see Volga as an ugly duckling, dragging along 'legacy' equipment. But with this 'legacy' equipment (the MSC) being on an IP evolution path as well, I don't quite see it this way.

So, I wish the companies speaking in 'One Voice' a lot of luck (I like the naming twist!) because no matter which approach will prevail in the end, we need voice services for LTE with proper CS interworking and we need it sooner than later!

And one more thought: I can imagine, and I actually think it's quite likely, that there will be more than a single solution for Voice over LTE deployed in the future. Competition often helps to speed things up. The good news is, it should be fairly transparent for the user as interoperability is ensured via the 'legacy equipment'.

3 thoughts on “The IMS One Voice Profile – Some Thoughts”

  1. It is interesting, in at least, this brings more recognition to no good solution for VoLTE. I agree that there will be other solutions that emerge including “simple” SIP servers and CS fallback.

    With over the top applications growing and more the upcoming people willing to use them, by the time LTE rolls out there could be a decent amount of voice that is just data. True mobility to 2G will not be supported; however one could make a case for 3G in that HSPA is supporting voice as is DOrA (in 3GPP2 networks). It would be the same as data service handoff.

    Net neutrality coming to wireless?

  2. Hi Martin,

    First of all congratulations! Your site brings a lot of valuable information in the wireless arena. I just had some thoughts about voice and LTE for existing GSM operators. The CS fallback and VoLGA solutions are overall designed to ensure call continuity between LTE and GSM. Is this correct? If we look at the statistics of existing GSM networks today, in average, you have less than 1 handover per call. This means that in majority of the situations the end-user is connected to the same cell during a call. Besides that, GSM coverage is really good by itself. Why then not using a handset that supports GSM and LTE without interworking? The same way that we are using today 3G and Wi-Fi or WiMAX and GSM together? I do not see the big added value of making a handover between LTE and GSM. Because if I am under LTE coverage, I am for sure under GSM coverage. Thus if I have a phone that is able to detect both technologies at the same time I am happy even if I cannot do handover between them. I was just talking about voice of course because data is another issue: if I have a Mobile Broadband subscription, I would like to take advantage of the largest coverage the operator can offer me even if it is not a high speed coverage in the whole country. I prefer to have a GPRS, EDGE, R99, HSDPA/DCH or HSDPA/HSUPA connection than nothing in the areas where LTE is not present.
    I think that voice could be important with LTE for the greenfield operators that do not have the GSM coverage. But as they do not have the GSM coverage, interworking between legacy network and LTE is not an issue anymore for them.

    Best regards,


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