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Are GSM and UMTS similar, or completely different?

Discussion in 'Off Topic' started by Moleculor, Mar 29, 2011.

  1. Moleculor

    Moleculor Newbie
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    Ok. I think I've gotten confused at some point.

    GSM. That does voice, obviously. Does it also do the whole data thing too? I see phones with GSM frequencies listed, and I see phones with UMTS frequencies listed, and somewhere I think I got the idea that GSM was for voice, and UMTS was for data.

    Is that not the case? Does GSM do both, and UMTS do both, but they're almost as different as GSM and CDMA? Or something? I realize that TECHNICALLY UMTS is based on GSM, but functionally, are they as different as GSM and CDMA, from a consumer perspective?

    (Basically, I'm looking to buy my first phone in about five years. Someone got me confused and told me that some phones only work on certain data networks, and others only work on certain other networks, and the two never meet, even if they're both GSM phones. Huh?)
     

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  2. Knewz

    Knewz Android Expert
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    UMTS phones support GSM. So if you have a UMTS phone it will work on a GSM network. But some phones will only work on certain gsm networks. Most phones produced today are at least tri-band so you shouldn't run into that problem though.
     
  3. Moleculor

    Moleculor Newbie
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    My only concern is data network compatability. Every Android phone out there is quad-band GSM, so I don't need to worry about that aspect of it.

    So is data done over GSM, or UMTS, for GSM phones? Or something else entirely? (My understanding is it's UMTS.)
     
  4. TheBrit

    TheBrit Android Expert
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    All of the above. It depends on the cell tower.

    The data layer for GSM is called GPRS - General Packet Radio Service. There's an upgrade to this called EDGE - Enhanced Data Rates for GSM Evolution.

    GSM is uses a system called TDMA - Time Division Multiple Access for multiplexing serveral calls on one channel.

    This is how it was until UMTS came along. This is how it is on cell towers that have not been upgraded.

    Along comes UMTS - Universal Mobile Telecommunications System which allows for both voice and data. It uses a system called W-CDMA - Wideband Code Division Multiple Access for multiplexing serveral calls on one channel. This is not compatible with the CDMA used by Sprint and Verizon in the USA.

    The there's an upgrade to the data service on UMTS called HSPA - High Speed Packet Access. This splits into uplink and downlink as in HSUPA and HSDPA that you can see mentioned sometimes. This is further being upgraded to HSPA+ which is much faster and is being marketed as 4G but isn't really 4G - more like 3.75G. Proper 4G requires LTE - Long Term Evolution.

    GSM and UMTS are completely different technologies. Handsets with UMTS tend to have GSM in them as well just so that they can fall back to GSM when UMTS is not available.
     
  5. Moleculor

    Moleculor Newbie
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    Ok. Which of those is responsible for data? Both? Neither?

    Basically, I want to know what to look for so that I get a phone that is compatible with as many data networks as possible. I DON'T want to buy a $500 phone and then find out it's never going to go faster than 2G speeds because I bought one that runs on the wrong frequency on GSM or UMTS or whatever data comes over.
     
  6. TheBrit

    TheBrit Android Expert
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    Ah, UMTS frequencies...that's a whole other ball game.

    Both GSM and UMTS can carry data - UMTS faster, HSPA (using UMTS) faster still.

    GSM = 2G, EDGE = 2.5G, UMTS = 3G, HSPA = 3.5G, HSPA+ = 3.75G, LTE = 4G.

    Look here for UMTS Frequences.

    With GSM it was easy. Europe use 900 and 1800 MHz, North America use 850 and 1700 MHz. A quad band GMS phone would work in any of those environments.

    With UMTS it's not so simple. Look at the Wiki article that I linked. If you can work it out the you're doing better than me. ;)
     
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  7. Moleculor

    Moleculor Newbie
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    Science!

    Ok. So...

    GSM/EDGE = GSM frequencies
    UMTS/HSPA/HSPA+/LTE = UMTS frequencies

    Correct?

    (Bloody hell.)

    And, if I'm understanding this correctly...

    AT&T = 1900 UMTS
    T-Mobile 1700 UMTS

    Correct?
     

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