UMA For Android Shows How Easy Voice Over LTE Can Be

Here's a press report I picked up recently from Kineto, who've ported their UMA protocol stack and application to Android Froyo. This may sound a bit cryptic but it has interesting implications for Voice over LTE.

For those of you who can't place the term UMA (Unlicensed Mobile Access), it's basically GSM voic calls over Wi-Fi. On the mobile device, all layers of the protocol stack of GSM are reused with the exception of the lowest layers where the UMA software introduces a switch so phone calls and signaling are either using the GSM infrastructure or a Wi-Fi access point that connects to the Internet. For the user its completely seamless. On the network side, the base station and the base station controler is replaced by a UMA gateway controler that connects to the Internet on the one side and to the network operator's core network on the other. To the core network the gateway looks like a GSM base station controler which makes UMA also transparent to the core network, i.e. no software or hardware chagnes needed there at all.

So UMA on Android, what does that have to do with voice over LTE? Well, as you might be aware of, there's no built in voice telephony functionality in LTE. That's why a number of different options have been suggested, one of them being Voice over LTE via GAN, or VoLGA for short. Now GAN (Generic Access Network) is just a synonym for UMA and that already tells most of the story. Volga replaces the Wi-Fi layer of UMA with LTE.

In other words, to close the circle, there's only little work required to modify the UMA Client for Android to use not only a Wi-Fi network but also an LTE network once Android LTE devices become available. With a client available for Android, operator based Voice over IP has arrived in the smarphone space (beyond RIM) and on an operating system that will play a major role in future LTE devices. And the work to make the software work with LTE is almost trivial since both Wi-Fi and LTE are IP based networks. So 99.9% of the software don't care if Wi-Fi or LTE is used for the transport of the IP packets that contain the speech data of an ongoing voice call.

One additional thing that requires a bit more work is the handover of an ongoing voice call from LTE to GSM (or UMTS) when the user is at the coverage limit of the LTE network. But like UMA, which is a 3GPP standardized technology, 3GPP also comes to help out here as there are already methods defined to do just that. The functionality is referred to a Single Radio Voice Call Continuity (SR-VCC). Specified in a generic way it can be used for IMS and also for Volga and potentially other solutions in the future.

While it takes a bit of work to implement SR-VCC into Volga, its fully specified and well worth to be done, as LTE – GSM handover of voice calls is a network operator's biggest asset to stay relevant in the voice call domain in the future as over the top voice applications have no way of doing that.

5 thoughts on “UMA For Android Shows How Easy Voice Over LTE Can Be”

  1. You really need to look beyond the technology and get to the support levels. Only one operator in the world supports VoLGA, and even they see it as an ‘interim’ solution prior to IMS. Having a fragmented voice space kills economy of scale, roaming and interoperability. The industry is going to IMS, so having more options is a bad thing, not a good one.

    And while UMA is 3GPP standardised, VoLGA isn’t. The GSMA work on IMS-based Voice for LTE is built on 3GPP MMTel work and is backed by 3GPP (and the entire operator community… and an awful lot of vendors).

  2. Martin,

    Very perceptive. Kineto’s UMA/GAN client for Android is nearly identical to what is needed to provide voice over LTE with VoLGA. And it’s available today.


    I know we’ve talked about this before… I still have trouble seeing how VoLGA, which uses the same voice core network that’s carrying phone calls for more than 4,000,000,000 people today, is ‘fragmenting’ the market. VoLGA bolts on to this same voice network, uses the same billing, the same OSS, the same BSS…. No fragmentation required.

    I think looking ahead ten years from now, when operators still have that same voice core network (used for 3G, and GSM), and have now implement an IMS network to provide voice for LTE, that things get fragmented.

    Maybe we should look beyond the technology, and evaluate voice over LTE with an eye towards cost to implement and return on investment.

    But that’s just my opinion.

  3. Steve

    It’s not just about networks. It is also about devices and roaming (as we have discussed before).

    I don’t think you believe that every operator will deploy VoLGA, which means you would have to accept that other operators will do other things. That is fragmentation.

    To get to the GAN-based elements in the operator network, there is a need to support some mechanism to identify that what is happening is a VoLGA call. If a non-VoLGA device roams into a VoLGA network (or vice versa) there is going to be a mismatch in supported technology between device and network. So if I roam with a non-VoLGA device into a VoLGA network (or vice versa), what happens to my voice service? Does it work? Does it fall back to CS? What happens if I need to make an emergency call – does it get routed to my home network (because the visited network just sees a data session even though a voice call is embedded within it)? If it is an IMS device in a VoLGA network does it route calls back to the home network as well? What about the mismatch in roaming commercial models? That is fragmentation.

    If you have every operator and every device manufacturer on the planet prepared to support all the bits for VoLGA, just in case a VoLGA customer roams in to a network that doesn’t support VoLGA or vice versa, then great, but you don’t and as a result for some scenarios, stuff gets broken. That is fragmentation.

    GSM-based voice allows economy of scale and roaming to happen because everyone in the GSM community implements the service in the same way. If we end up with multiple implementations for voice over LTE it all becomes fra… nah, I’m not going to say it again.

  4. Martin-

    Interesting article. I am just an end-user in this instance, but what I am wondering is whether you or anyone else knows whether this technology will only be available on newly marketed handsets or whether some form will be developed that can be backwards-compatible to cell phones that are already on the market (via an application or firmware update)?

  5. Hi Kevin,

    I guess you are referring to the GAN client for Android. Whether or not the client can be retrofitted is probably a question to ask network operators that offer GAN and Android handsets. I dont have any info on that.

    Kind regards,

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