AT&T iP5 switches to 4G from LTE when placing a phone call

Discussion in 'iPhone' started by soulvoid, Sep 24, 2012.

  1. soulvoid macrumors member

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    Sep 5, 2007
    #1
    Please explain why this happens. I know Verizon and sprint can't handle voice and data at the same time on LTE but AT&T can. So why the switching? Is the 4G network handling all the voice calls for now until the LTE network is mature or what?

    I can't be the only one this affects either. Please chime in. Thanks
     
  2. Shaddow825 macrumors 6502

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    #2
    Both versions can only support one type of a connection at a time. Neither Verizon nor ATT support VoLTE yet so each drop down to the GSM or CDMA network for calls. GSM then supports data over the same connection as it always has.
     
  3. penajmz macrumors 68030

    penajmz

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    #3
    Because LTE + Voice calls require 2 chips the iPhone 5 does not have, it only has one.
     
  4. Radiating macrumors 65816

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    #4
    No carrier in the world supports voice over LTE. Voice over LTE is a new thing that is being prototyped to send higher quality voice signals over LTE, but until that's implemented in 1-2 years LTE is only for data period for everyone worldwide.
     
  5. soulvoid thread starter macrumors member

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    #5
    That's all fine and dandy but... Is the reason LTE doesn't support VoLTE currently because the network infrastructure isn't robust enough or the specification doesn't handle it period? Before I posted and ran across something pertaining to this about Verizon's LTE but not AT&T.
     
  6. Shaddow825 macrumors 6502

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    #6
    Actually MetroPCS has rolled it out in some markets and will be networkwide in the next few months.
     
  7. soulvoid thread starter macrumors member

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    #7
    Ahh ok. So disregard my last post then. So the spec support it but not for mass market yet. Gotcha.
     
  8. Shaddow825 macrumors 6502

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    #8
    Neither have rolled out support for in in their switches. And I do not know for certain that the software in the iphone 5 supports it even in the future when it is rolled out.
     
  9. soulvoid thread starter macrumors member

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    #9
    If true, then wtf big 3...
     
  10. milan03 macrumors 6502

    milan03

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    #10
    Pretty much all of these answers are wrong. That said, here is why it switches to "4G""

    It's called Circuit Switched Fallback", and it's a normal behavior of a GSM/HSPA/LTE network when calls are made/received. LTE doesn't support voice at the moment, it's data only, that should change maybe in a year or so with VoLTE (once VoLTE codecs and fallback is standardized), but each time you make a call the baseband chipset has to fallback to HSPA to prioritize Voice. This is the only possible way to do it. The benefit is that you're still able to talk+surf at the same time, just not on LTE.

    CDMA networks behave similar except that you fallback to 1XRTT where talk+Surf isn't supported at the same time. A complete extra set of antenna setup would've been needed to achieve talk+surf on CDMA network.

    Hope this helps.
     
  11. xak macrumors regular

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    Mar 13, 2012
    #11
    I use AT&T. My current iPhone 4 can make calls and surf the internet simultaneously on 3G. Why doesn't the iPhone 5 send voice over 3G and keep the data flowing through LTE?
     
  12. soulvoid thread starter macrumors member

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    #12
    I appreciate the technical answer. And commend you for doing so :)
     
  13. Radiating macrumors 65816

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    #13
    Actually my mistake I checked up on the issue:

    They've already gone past the prototype stage and are starting very very early adoption in select markets with specially designed devices.

    Long story short:

    In August 2012 VoLTE (Voice over LTE) has been activated in South Korea.

    In August 2012 Metro PCS has activated VoLTE AND has released a phone which works with it: LG Connect 4G in Texas
     
  14. soulvoid thread starter macrumors member

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    #14
    Something about the number of antennas and radios it can use at the same time. Hey technical answer guy. Chime in on this one eh?
     
  15. soulvoid thread starter macrumors member

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    Sep 5, 2007
    #15
    So will this be enabled for us AT&T ip5 guys with a software/baseband update or the iphone5S or 6? What's the tech tell us...
     
  16. milan03 macrumors 6502

    milan03

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    #16
    That would require a whole other radio and it wouldn't be efficient at all. Battery would suffer and also i doubt FCC would allow that to happen due to the increased radiation SAR level. You're basically broadcasting voice + data on HSPA and on top of that LTE.
     
  17. Radiating macrumors 65816

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    #17
    The iPhone 5 already has HD Voice from the factory which is another name for Voice Over LTE. This was discussed on a slide in the keynote.

    As soon as the carriers support it it will work. No update nessesary.
     
  18. soulvoid thread starter macrumors member

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    #18
    Word. I like this :)
     
  19. shaddix macrumors newbie

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    #19
    Every other LTE device on Verizon supports simultaneous voice + data with LTE coverage, the iPhone is the only device that does not. I was hoping I would be able to make the switch from android to iphone this time, but sadly I cannot, and only for a small decrease in form factor. Currently I can work remote and take work calls simultaneously with my android device, and this should have been possible with the LTE iPhone but they screwed it up. As you can see I'm a little butthurt.

    (In fact there is one device (Thunderbolt) that supports voice+data with Verizon 3G coverage.)
     
  20. milan03 macrumors 6502

    milan03

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    #20
    HD Voice isn't VoLTE. HD Voice is the wideband codec made for WCDMA networks. 20 European GSM/HSPA carriers will be using this.
    It's a completely different thing.
     
  21. Radiating macrumors 65816

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    #21
    That's because they use two chips, which uses a ton of battery power. The iPhone 5 uses 1 chip, and a lot of effort went into making it this way. Just wait until Voice over LTE is turned on.

    Interesting, I read on a blog otherwise, but I guess they were definetly missinformed after reading some more. well regardless the iPhone 5 supports VoLTE, which is where the voice information is sent as a data packet through the LTE data connection.
     
  22. milan03 macrumors 6502

    milan03

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    #22
    Well the interesting thing is MDM9615 Baseband chipset in the iPhone 5 supports VoLTE, but according to FCC testing, it's not actually active in iPhone 5. So it really doesn't support, and if they're to update it, it would've required another trip to FCC.

    VoLTE in the U.S. is still far from being a wide spread solution. Verizon announced VoLTE deployment once they completely blanket their existing 3G footprint with LTE, and AT&T didn't even announce any VoLTE path. The problem they're facing is that codec isn't really standardized globally so they're not commiting, and also calls made from VoLTE solution to regular landline or GSM/CDMA would need to scale and that's still not ironed out from the technical standpoint.

    MetroPCS on the other hand already has VoLTE deployed in one market, but it's a poor narrowband codec that doesn't do much. They just like to be first lol :)
     
  23. vistadude macrumors 65816

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    #23
    It's so they can throttle you and give you an explanation why throttling you saves you battery.
     
  24. milan03 macrumors 6502

    milan03

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    #24
    Wait... what?
     
  25. Applejuiced macrumors Westmere

    Applejuiced

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    #25
    Time to switch to AT&T:D
     

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