Explain the technology behind why att's 3G does voice and data Simultaneously

Discussion in 'iPhone' started by Bonds79, May 1, 2011.

  1. Bonds79 macrumors 6502

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    #1
    Explain the technology behind why att's 3G does voice and data Simultaneously and CDMA does not?
    Does att 3G use Edge for voice while HSPA for data? or does att HSPA convert everything thing to data including voice?
     
  2. appleguy123 macrumors 603

    appleguy123

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    #2
    I think that CDMA has data and voice on different frequencies while GSM has them on the same frequency, but I may have that reversed...
     
  3. maclaptop macrumors 65816

    maclaptop

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    #3
    Using the words of the worlds greatest sales person, "It's Magical & Revolutionary".
     
  4. grapes911 Moderator emeritus

    grapes911

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    CDMA has two different channels. One is for voice, 1xRTT. One is for data, EvDO. While the technology technically could support using both at the same time, the standard does not. Verizon implements the standard as it was written. Recently the CDMA Development Group published an optional CDMA specification that will allow both to be used. I don't think anyone implemented it yet, and the probably won't with LTE right around the corner.

    AT&T uses a different standard where voice and data is sent over the same pipe. They do not separate voice and data over different channels, and yet it still allows voice and data signals to be sent at the same time.
     
  5. YaBoiD macrumors regular

    YaBoiD

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    #5
    Verizon implemented simultaneous voice/data on EVDO-Rev A (can also be done through LTE) using the ThunderBolt but this is the first and only smartphone with this feature so far.
     
  6. grapes911 Moderator emeritus

    grapes911

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    #6
    I thought simultaneous voice and data wasn't until Rev. B, which Verizon has not implemented.

    You are correct in saying that LTE handles it, but that is a completely different technology from CDMA.
     
  7. wordoflife macrumors 604

    wordoflife

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    #7
    So if Verizon allowed phones to connect to both channels simultaneously, Verizon would have simultaneous voice+data?
     
  8. grapes911 Moderator emeritus

    grapes911

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    #8
    I guess yes. As far as I know, there isn't anything technically stopping them from doing so. The issue is that that isn't how the standard is written.

    There is also something called Voice over Rev A (VoRA), also know as SVDO. This may be what YaBoiD is referring to. Maybe Verizon is trying to roll that out, but I'm not sure. I think that is a "patch" on top of Rev. A. I guess it pulls back features of Rev. B to work on Rev. A, but I don't know all the details.
     
  9. kdarling macrumors demi-god

    kdarling

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    #9
    -- CDMA2000 phones:

    VoRA is voice over the data channel. Requires network changes.

    SVDO (Simultanous Voice and EVDO) uses the physical or software equivalent of two radios to connect to the voice and data channels at the same time. Supposedly requires no network changes.

    --- GSM phones:

    Left alone, GSM phones usually use their TDMA (2G) radio for voice connections.

    If a data attempt occurs during a 2G call, the phone requests a 3G connection and then drops the 2G voice call, so it can flip over to sending both voice and data over 3G. (This is where calls go bye-bye sometimes. You might not even realize that your phone had requested to send data in the background. You just know your voice call dropped for mysterious reasons.)

    So when GSM phones use simultaneous voice and data, it's done via their 3G WCDMA radio. The 'W' = wideband, which is the secret. It has more bandwidth room for sending voice + data at the same time and/or for speed.
     
  10. Krevnik macrumors 68040

    Krevnik

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    #10
    Yup, it is SVDO in the Thunderbolt. CDMA isn't going away anytime soon even with LTE coming into the picture, so it makes sense to try to deploy SVDO when it doesn't require network changes to do it.
     

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