LTE Voice: the more I've looked at Circuit fallback, the worse it's looked

I've been talking about the problems with voice on LTE for more than two years now. I first published a report on VoIPo3G in November 2007 in which I discussed in great detail the problems with IMS voice, and the fact that there was no simple, standardised version of "basic VoIP" suitable for operator deployment. I'd previously written about the issues with IMS-capable handsets in 2006, and VoWLAN the year before. More generally, I've been covering wireless VoIP since about 2001.

A common strand in my analysis has been that the technical standards are often completely divorced from considerations of end-user behaviour and experience, the needs of application developers, the practicalities of handset design and the realities of business models.

Like politicians, there's instead usually a focus on control and ideology, rather than pragmatism.

That's not to say that every new technology development has to start with some sort of fluffy "inclusive" focus group approach, or that pseudo-cartels should invent things that competition authorities will frown upon.

It often just means that more consideration needs to be paid to questions like:

• "Hang on a minute - how's this actually going to look in the hands of the user?" or
• "Isn't this going to make it worse than the older solution people have already? Who's going to buy that?" or
• "Isn't that going to break all the other applications running on the phone? What happens if it's multi-tasking?"

A very good example of this is one of the proposed standards for providing voice over LTE networks, Circuit Switched Fall Back (CSFB). This is the 3GPP approach to supporting voice which drops the LTE connection back to 2G or 3G to make or recieve a phone call. It is generally positioned as an "interim" solution before moving to full IMS voice.

I've written before about CSFB, and it's also been discussed in many of the comments threads on my previous posts on LTE voice, such as here, here, here and here - many of which also cover ongoing problems with IMS voice. (The recent OneVoice announcement is a possible medium-term solution to some of those problems).

Some of the issues that keep cropping up include the latency involved in the LTE-to-3G/2G process, the impacts on any data applications running on LTE at the time of a call, and the need to have overlapping coverage of older networks everywhere you put LTE.

I've now done a more thorough analysis of CS Fallback's flaws. I've come to the conclusion that it's not just awkward, it's actually terrible - worse than useless, in its current incarnation at least. Going back to my questions before, it seems clear that nobody ever said something like:

"Hang on a minute, LTE phones will be expensive, so our best customers will buy them first.... but it will give them a worse telephony experience with CSFB than their existing handset. That's never going to fly!."

(Incidentally, coming back to a discussion from another thread, one commenter asserted that fallback could be achieved in about one second. I cited 2-4secs, based on a 3GPP submission I'd seen, and we agreed to disagree in the absence of hard evidence. I spoke to a *very* senior person in handset RF development for a major device vendor earlier in the week, who has more cellular patents than I've had hot dinners. His estimate was for 6-12 seconds extra latency. For an LTE-to-LTE call or SMS, it would be quicker to use Morse code).

I've now written a white paper covering CSFB's major flaws, which actually seem pretty extensive even beyond what I've written above. It almost looks like it was designed to make IMS voice look good by comparison.

The paper is available for download from here. But first, some disclosure. It has been commissioned by Kineto Wireless, the chief proponents of the main alternative VoLGA, which has evolved from UMA/GAN. In common with all Disruptive Analysis' sponsored material, I only take on topics where I already have a strong opinion - I'd written positively about VoLGA since March , despite having been a thorn in UMA's side since its launch in 2004. (I'm convinced that somewhere in Kineto HQ is a dartboard with a picture of my face on it). It's not perfect either, but it seems much better than CSFB or IMS.

I'd also previously written about CS over HSPA (which is the same basic principle of 2G voice over a 3G IP bearer) in early 2008. I'd even originally suggested doing "2G over 3G" as a possible better use case for UMA than WiFi, way back in 2005/6, albeit a bit flippantly at the time.

The bottom line is that I think that 3GPP should reconsider VoLGA or something close to it. CS Fallback looks like a terrible interim solution for voice-on-LTE, especially for operators who aren't sure that their particular endpoint is IMS voice. The current two-solution approach (CSFB / IMS) seems guaranteed to either promote 3rd-party VoIP solutions, or delay LTE entirely. If the whole thing *has* been some sort of standards conspiracy to force IMS into the hands of the unwilling, I'd make a suggestion to include some game theorists in the discussion next time.

One thing I should note for completeness is that there are a couple of other options out there, notably NSN's Fast Track and another from Acme Packet and Mavenir. I haven't had a chance to drill into those as much, but from an external perspective they don't seem to have as much traction or behind-the-scenes support as VoLGA.

Once again, the white paper on why I feel CSFB is "not fit for purpose" is here.