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Summary:

Qualcomm and Ericsson have successfully passed a voice call from an LTE network to a 3G one, paving the way for mobile carriers to begin migrating their voice traffic onto all-IP 4G networks. Once that happens, operators can start shutting down their 2G and 3G networks.

Baton handover hand off

Qualcomm and Ericsson revealed on Thursday that they have successfully passed a voice call from an LTE network to a 3G one, paving the way for mobile carriers to begin migrating their voice traffic onto all-IP 4G networks. That’s a big deal because the sooner carriers move their voice and SMS services to LTE, the sooner they can shut down their pokey 2G and 3G networks and establish a mobile broadband continuum across the airwaves.

First some acronyms: the technology Qualcomm and Ericsson successfully trialed is called SRVCC – single-radio voice call continuity – which is a critical step in migrating today’s old-fashioned circuit-switched voice networks to the IP world of VoLTE, or voice over LTE. Today’s LTE networks rely on a standard called CSFB (circuit-switched fallback) to handle voice calls, which is to say they don’t. AT&T LTE network uses CSFB in its phones to detect an incoming call and then shunts the radio down 2G or 3G mode, where Ma Bell’s reliable old voice switches can take over.

CDMA operators like Verizon Wireless don’t even use CSFB. Instead they maintain dual 2G and LTE connections, ensuring you can always receive a call or SMS, but playing havoc with your battery life.

SRVCC will allow operators that use CSFB to gradually introduce VoIP onto their LTE networks because they don’t need worry about what happens when customers leave 4G coverage. When the network decides to convert the call from IP to circuit, it simply switches radio modes, theoretically maintaining a seamless connection all the while.

Verizon won’t be able to take advantage of those capabilities, but it feels it won’t need to by the time it launches VoIP this year or next. It plans to have LTE coverage in so many places, its customers will never have to leave its 4G network unless they travel way out into the boondocks. If a customer does actually leave the LTE network while making a call, that call would drop, but Verizon CTO Tony Melone said that instance would be rare enough that the carrier simply isn’t going to worry about it. In fact, Verizon is so confident of its LTE network’s ubiquity, it plans to launch its first LTE-only phones in 2013, making 2G handover a moot point.

So when will we start seeing these new VoLTE services appear? Sooner than you might think, actually, but not from Verizon or AT&T. Small, feisty MetroPCS will likely be the first North American operator to migrate to VoIP, and with good reason. Its LTE network is limited in capacity compared to its larger competitors, and as soon as it can start handling calls on 4G it can start shutting down its CDMA networks, re-farming their spectrum for LTE. MetroPCS has already moved its SMS traffic to LTE, and CEO Roger Linquist has said it plans to launch VoLTE this quarter

  1. The Voice on Telecom Friday, February 3, 2012

    Smaller and cheapter and faster smartphones, better battery life, better voice quality. This only means good things, especially as it is an industry-leading chipset. With so many hybrid services rising up, handover is going to be a huge issue, and this puts LTE networks in the front seat.

    thevoiceontelecom.blogspot.com

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  2. Kevin Mitchell Friday, February 3, 2012

    Note that this hand-off between LTE and 3G is only relevant for the GSM crowd and not the CDMA operators like MetroPCS. Verizon is going coverage strategy to minimize instances of call drops but they will not have a hand off domestically (for roaming internationally they may need a solution).

    Further, CFSB is only a GSM standard. The CDMA-LTE voice combos are 2 active radios at the same time. CSFB is a 3GPP standard that has LTE active first and then turns off that radio when a call is made. It falls back to 3G to make that possible. It’s wickedly backward and means you can’t surf and call at same time (that’s so CDMA!).

    There is a 3GPP2 standard for so called Single Radio Voice Call Continuity (maybe using another term) but as far as I know there aren’t any vendors building a solution.

    Kevin Mitchell

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    1. Kevin Fitchard Friday, February 3, 2012

      Hi Kevin,

      Isn’t that what I said? :)

      It is kind of funny that AT&T and Verizon have swapped places in the whole surf and talk debate with LTE.

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      1. Kevin Mitchell Friday, February 3, 2012

        Yes, and very well! I wanted to explicitly emphasize that its due to standards vs choice.

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    2. Kevin, CSFB applies to CDMA as well. We have developed it for KDDI in Japan where the key driver is long battery life (single-radio) handsets and maintenance of excellent call quality (on their 1x system). VZW and/or Sprint could just as easily do CSFB although it is a strategic decision and the time window for that may have passed (ie they are stuck with what they decided already).

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  3. William Diaz ✔ Friday, February 3, 2012

    The whole call handoff and and the whole simultaneous voice and data will not be an issue in just a few years anyway. In the case of CDMA, having two radios on is killing the network and battery life. Being connected to two networks to have the capability of voice and data, is really hogging up resources.

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  4. There are many benefits for the carriers to deploy VoLTE, however I think one of the best opportunities is that VoLTE in and of itself is a new platform for innovation. I expect that we’ll see a plethora of new service offerings created by the developer community. These apps and services will complement, and in some cases compete, with VoLTE offerings from the carriers themselves.

    My $.02,

    Best.

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    1. Kevin Fitchard Friday, February 3, 2012

      Good point, Curtis.

      We talk about VoLTE in terms of voice, but the big benefits come from the reams of SIP-based services that come with an IMS-driven VoIP (sorry to toss in more acronyms). It would be very cool to see voice integrated directly into apps, transferring a voice call to video and vice versa, etc.

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      1. Kevin Mitchell Friday, February 3, 2012

        Well said. VZW has said that it’s not just voice but rich communications when they launch. I think they’ll be the exception to the rule, but overall that is why IMS was chosen vs other approaches: it a singular architecture for all services and the path beyond voice and messaging.

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      2. Kevin Fitchard Friday, February 3, 2012

        I have to wonder if Verizon is having second thoughts about the VoLTE-IMS rollout though. Signaling problems and IMS glitches shut down their LTE network three times in December. Won’t SIP-based voice and enhanced services add a tremendous signaling load? Any insight, Kevin?

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      3. Kevin Mitchell Friday, February 3, 2012

        seems I can’t reply to a reply to a reply.

        Kevin: the signaling load would be different and managed by the IMS network. VoLTE adds SIP signaling to the mix and the dynamics for that protocol are different (although signaling controls share many similarities with the other major LTE IP signaling protocol: Diameter). Given the scale that VZW is undertaking for LTE overall, the VoLTE service roll-out is certainly a major effort but delaying VoLTE I don’t think can be in the cards.

        I don’t know specifics on the LTE network glitches, but I know they are not SIP related.

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