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Mobile Identification on BTS

Viewing 7 posts - 1 through 7 (of 7 total)
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  • #67753
    Deepak Sood

    Hi Experts,

    I don’t know if this is even a right question to ask but i am little confused regarding that when two diff MS are transmitting and receiving data or even a simple GSM call latched on some particular Cell. Then does BTS receives info taking consideration of their specific identities, or its just that the Time slot no. works and no identification is required after authentication.

    I may have made it little vague but the thing is somebody asked about this regarding GPRS/EDGE data that how come a cell identifies data coming from two diff MS latched on it.

    eagerly waiting for a reply…


    hi deepak,

    in GSM, during a voice call, the MS is allocated on one circuit only. There is no risk of confusion between several MS, because one circuit = one call.
    A circuit in GSM is a radio timeslot, which is identified by its timeslot number and by its ARFCN.

    In EGPRS however, one radio timeslot can carry several users (up to 6, usually) and as you noticed, such a system requires a need for each “block” sent on a RTS to be specifically identified.

    Back to voice call, in half rate, two users are sharing one timeslot. But each user is actually using exactly one timeslot every other two. The scheduling is static, which prevents possible confusion.
    In EGPRS the scheduling is dynamic.


    Deepak Sood

    Hi Pix

    Thanks a lot for the info, actually the guy who asked this, asked it specifically for EGPRS now i can see why. Actually i’m not much of a GPRS person tight hands actually:). But i guess the question still persists that how the MS will be identified on RTS something by IMSI i guess….

    BTW i have been following your posts for a quite a time and i must say that u take a great care to make them crystal clear…thanks for your valuable opinions and precious time….



    thanks 😉 I’m glad I can help. On the other hand, “westbay engineers” is paying me 100$ per post.

    (I wish)

    To come back to your initial question… I don’t mind spending time on it, so let’s go as deep as you need !

    The BSC allocated the voice call on a specific TS, so there is no need to identify anything else after the call setup. The call will always be on that RTS.
    Therefore there is no need to identify each burst sent on this RTS. The BSC knows that they all belong to one subscriber.
    At call setup, of course, the MS is identified and authenticated thanks to its IMSI/TMSI, and those checks are done by the core network. But that is of no interest to the BSC.
    The BSC only maps a specific call (identified by its SS7 id) to a RTS. After a HO, the BSC will map the SS7-id to another RTS.
    SS7-ID is the identifier of the call from a CN point of view.

    It does not identify one particular subscriber.

    Indeed, the BSC does not know anything about the subscriber ! It only sees the subscriber as a “call”, nothing else.


    Forum moderator

    “On the other hand, “westbay engineers” is paying me 100$ per post.”

    (I wish)”

    You would a very rich man if that were true ;). Anyway, your input is always very welcome.


    hi mod’,
    good to know you are keeping an eye on us ! Few more days and I was gonna charge the other members for my answers. You just brought me back to my senses :))


    Deepak Sood

    Hi Pix

    So in EGPRS where the RTS is taking 6 users max i guess…dosen’t it require the info of the subscribers while commmunication, by communication i don’t mean authentication i.e. after call setup has been done.Well what you said above regarding RTS and SS7 mapping works for voice and GPRS too, BTW that was unknown to me and thanks for throwing light on this.

    And hi Mr. moderator

    This is the first post i have seen from your side…….nice hope to see more of them..

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