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ATT flag

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  • #67439 Reply

    Good evening, GSM experts!

    I would be very grateful for your help in one question:

    What is the danger of having ATT(IMSI attach/detach) flag = 0 (disable)?
    For some reason we had to set this parameter to DISABLE for several cells and I wonder which problem should I expect.

    Thank you very much in advance.

    BR, AngeloP

    #67440 Reply


    ATT = Disable means that the MS is not able to IMSI-ATTACH to the network in this cell. So when someone turns on its phone in this area, its phone won’t attach.
    As a consequence, this phone is not reachable if someone tries to call it.
    On the other hand, it is possible to make a call. And as soon as the call is being made, the MS becomes de facto attached. Therefore it will be reachable for the next “T3212” hours.
    i wonder what “logical” reason you had when you decided to set it to disable, not even knowing what this parameter does 🙂
    I’m sure they had very logical reasons to build a nuclear plant in Fukushima…


    #67441 Reply

    Hello, Pix!

    Thanks for your reply.
    Actually, it was a recommendation from our support team.
    we have problem with high SDCCH drop in some cells and there are no evident causes for it

    so we inquired to them and got an answer to disable ATT flag

    that’s why i was a little bit worried for consequences

    thank you very much again


    #67442 Reply

    ok, that’s a good investigation method ! we noticed that huge SDCCH drops are caused by crazy MS doing a lot of location updates which are never succesful.

    But then, once you understand what’s going on in this particular cell, you will have to reactivate it again…


    #67443 Reply

    Hi Selva!

    There are some cases in which cell become overloaded with high traffic , so at that time network set ATT=0,
    So any MS/UE is switched off it will not ask resources from network to perform IMSI Detach .But as a disadvantage network try to page the MS/UE even it is not attached to n/w but compared to signalling load occur in performing detach is more if compared to paging ,so in that scenario its better to set ATT=0 and of course on expiry of mobile reachable timer MS/UE IMSI will be marked detached by the network. so overall to save the resources in case of heavy traffic in cell N/w set the ATT =0

    #67444 Reply


    What you said is very wrong….

    ATT allows the MS to send IMSI ATTACH… if you disallow ATT, the MS will never be attached, and it cannot be paged, unless it makes one call first (which will allow the NSS to attach this MS).

    The DETACH load is clearly NOT an issue in any network in the world… Location Area Updates are probably 1,000 times more numerous.

    #67445 Reply
    goli.bala nagarjuna

    in some cases when we poweron we will get location update instead of imsi attach . why? then is att enabled or disabled?

    #67446 Reply


    If ATT is Disable, then the MS is not allowed to send an IMSI ATTACH in the cell.
    If ATT=Enable, then the MS is allowed to do it, therefore it will do it at Switch On.
    Indeed, IMSI ATTACH is only done at MS Switch On, or when switching off the “Airplane” Mode.

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