Why can't we do simultaneous voice and data?Support


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  1. JohnJSal

    JohnJSal Well-Known Member This Topic's Starter

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    If you don't need 3G on to do voice calls, then why would having it on not allow you to use your data connection while on a voice call?
     

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  2. aaz110

    aaz110 Well-Known Member

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    It's a limitation of CDMA itself (and all current CDMA phones...not just our Evos). Current CDMA radios can't access both EV-DO (for data) and 1x circuit-switch voice calls. A solution has been announced and will supposedly arrive next year...but that would require a new phone with the new type of CDMA radio...all we will have with our Evos is simultaneous voice and data with the stipulation being through WiFi or 4G, as they use entirely separate radios.
     
  3. JohnJSal

    JohnJSal Well-Known Member This Topic's Starter

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    Ah, I guess I was seeing 1x and 3G as two separate things, since they could be toggled on and off individually, but you're saying they still basically come down to using the same internal hardware, so that's why?

    Thanks.
     
  4. Mr. Ed

    Mr. Ed Well-Known Member

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    Like he said...1 radio that can't do both at the same time. Haha...like trying to use both ends of a number 2 pencil simultaneously
     
  5. Palmetto Fellow

    Palmetto Fellow Well-Known Member

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    Voice packets need to go down the EVDO link when in 3G data mode and bypass the 1X voice.

    Which CODECs do CDMA cell phones support?

    Package it as SIP, and send it on it's way over the 3G EVDO link...this isn't that hard to do with smart people on your staff.

    Edited to add:

    Hardware chages to the radio are not needed to implement what I suggested...however, I don't know how QoS will suffer from this.
     
  6. boteman

    boteman Well-Known Member

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    I suspect that the quality of VoIP calls will be anywhere from slightly to significantly worse than cellular switched voice calls. Mobile data networks were designed to carry data, after all, and there has been a hell of a lot more R&D in getting the voice quality up to snuff.

    I have tried RTP over Sprint's mobile data network a couple years ago and the best I could achieve was "satisfactory", but the latency was horrible and if the r.f. signal was not pristine it suffered a lot of holes in the recovered voice. We had no means to set any QoS flags in our packets, however.

    The other posters are right on the money why you can't do voice and data simultaneously on a CDMA network. AT&T's W-CDMA network does allow simultaneous voice and data usage, a fact which they recently touted in a television ad campaign.

    These different air interfaces prevent one universal phone from roaming anywhere in the world. Maybe one day.
     
  7. JohnJSal

    JohnJSal Well-Known Member This Topic's Starter

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    Ah, that helps a lot!
     
  8. Palmetto Fellow

    Palmetto Fellow Well-Known Member

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    It's hard for me to see the seperation in the two networks...if one radio can serve them both. To me, it's the same technology being used in a different way. What's the bandwidth needed to place a cell call? And why is there so much more latency when using it for "data" rather than "voice"?

    BTW, there is a very fine line now between data and voice...voice is basically data nowadays. VLAN tagging, and other QoS measures are being inplemented to ensure that voice packets get priority over email packets, or streaming music. Almost all carrier grade routers nowadays recoginze the same form of voice prioritization. So if you hand packets to a different network, that network will also know they are voice, and will treat them with urgency. Sprint only needs to get your "3G Voice packets" back to the cell tower's base station. It can then push them out the normal trunk reserved for voice calls if this trunk is different than the one used for data.

    If I was Sprint, I would be working on ways to get more out of my hardware. GSM competitors can do voice and data at the same time (using two different radios). I'd be working on a way to give my customers similar functionality (with one radio)...and I've heard a rumor that they are in fact working on it...but it sounded like a hardware fix rather than a software fix to me. What I propose would be strictly software.


    Why hasn't this been done yet? Perhaps I don't realize the limitations with EVDO CDMA, or whatever you call it.
     
  9. boteman

    boteman Well-Known Member

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    What many people seem to forget is that these are wireless networks, not wired networks.

    Radio signals do not always do what we wish them to do. People go into sub-basements inside steel elevator cars and just can't seem to figure out why their phones no longer work. These things do have limitations.

    Remember, your phone is competing with hundreds or thousands of other phones out there to get a signal back to the cell site. There is interference from improperly installed bi-directional amps, active antennas, paging transmitters, and other random r.f. garbage. Sometimes a newbie engineer makes a change to a cell site or the switch that hoses up things. Sometimes the packets simply do not propagate through the ether to the cell site. All the tagging and QoS in the world won't change that, it's governed by the laws of physics. Once that packet is lost, it's gone forever.
     
  10. Palmetto Fellow

    Palmetto Fellow Well-Known Member

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    I hear what you're saying, but the 100K other phone comment seems a bit of an embellishment to me :p Cell towers don't usually connect hundreds of thousands of people do they?

    Packets are lost, and have to be retransmitted, but I often get 250k-512k of bandwidth with 200ms as the average ping. That should run VoIP just fine. How many packets do we drop on average currently with data-only 3G? I'll also point out that most of the things you mentioned that would interfere with an IP voice packet's transmission would affect a voice call as well (can you hear me now?). Choppy audio is better than NO AUDIO.

    Cram voice packets into the 3G data stream, and tag the hell out of it. Then you can offer voice and data at the same time. Software/Firmware updates only, no hardware changes should need to be made.

    Is the solution to add two EVDO radios to the phones? One to send voice and one for data? Each user (if they happen to receive a call) would need to take up two resources from the tower. I'm not saying it's mandatory for them to take up the resources...only if they are actively using data and on the phone. Eventually, this will use up space as more clients try to connect to the same towers.
     
  11. FreakyLocz14

    FreakyLocz14 Banned

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    You own an EVO? You can use simultaneous voice and data services without Wi-Fi. Sprint's 4G network uses an entirely different radio than it's CDMA 1x EV-DO radio does.
     
  12. Palmetto Fellow

    Palmetto Fellow Well-Known Member

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    Yes, by using two different radios, it's easy. But I can't see why they can't make it happen with the voice and data both riding on the 3G radio. It can be done. They aren't doing it, so perhaps they have a different method in mind. The CDMA Development Group has a press release out stating that CDMA2000 devices will "access EV-DO packet data services while in an active 1X circuit-switch voice call.
     
  13. sikclown

    sikclown Well-Known Member

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    Botman said hundreds OR thousands... not hundreds of thousands. If you read up on CDMA you will find that it is an extremely advanced and intricate technology as well as a very young and difficult one(in relation to GSM). They still have kinks to work out but I think the real answer is in the move to 4g services. Adding two CDMA EVDO radios to a phone would require two different numbers because of the way the technology works not to mention battery life would be even worse. CDMA radios eat significantly more battery because they are constantly polling for multiple towers where as GSM radios only poll for the next tower when they leave the current one (over simplification).
     
  14. bbuser

    bbuser New Member

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    With EVDO we can't use voice and data at the same time because EVDO technology is a hybrid of 2.5G and 3G technology.
    1X is used for voice calls and EVDO is used for data. The orginal name for EVDO is Evolution-Data Only. They rebranded to Evolution-Data Optimized because it sounded better.
     
  15. vwwv

    vwwv New Member

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    Old thread, but I thought I would add the problem with needing two radios is that the two uses are on different frequencies. In effect, you can't be tuned into both.
     
  16. balamuruga19

    balamuruga19 Member

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    Hi,

    In video calling phone. we are able to use data connection and voice both at same time. But If the phone is not supported for video calling, While making voice call data connection will disconnect automatically. We need to find the solution for this. something is difference for video calling phone and without video calling phone. So Nothing is difference with 3G technology.
     

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