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Random SD Congestion during weak hours

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  • #66521 Reply

    Hi all,
    In our network, there’s often heavy SD congestion during weak hours, where the traffic is not high(especially at midnight). This problem happens to many BSCs and there’s no problem with the nearby cells (belonging to the same or different BSC). Anyone can help me to find the reason for this?

    #66522 Reply

    Is this site near to any rail route?

    #66523 Reply

    This happen randomly, not in any certain cells or BSCs. I heard that in Ecrisson, they findout that there’s some bad behavior mobiles keep sending RACH request that lead to SD Congestion. This is quite strange because this problem just often happen only at night (if there are these mobile, why don’t they send RACh Request in datetime?).
    So if there are really the mobile like this, so what can we do to reduce the SD congestion in this situation?

    #66524 Reply


    you cannot prevent RACH..

    can you verify that those RACH are caused by Location Updates ?
    in those cells you could increase the T3212, so that the faulty MS would not do the periodic LU so often.

    During daytime, those MS are originating or terminating calls, so the LU timer T3212 does not expire.
    My assumptions is that the faulty behaviour occurs only during the expiry of the t3212 (periodic location update)…

    however, your problem is “virtual” : nobody will ever complain that there is sdcch congestion during the night. It doesn’t impact anyone.

    Also, you could try to activate the immediation assignment rejection, that should help.


    #66525 Reply

    I have had the same problem and after tracing the cell I found that one mobile requires 10sec for a location update and it keep asking every minute, normally it requires 2-3sec ask every 1.30h. I thought it was a strange mobile so I put him on trace but the next night it was ok. than another mobile on another cell was having the same problem. This problem does not happen very often on our network so its not a problem, but Im curious to know why?

    #66526 Reply


    the location updates takes 10s because it is “rejected” I guess. The core network does not answer to the LU REQ, so the MS is waiting 10s then it “drops” the sdcch.

    That’s a possible scenario, I’m not saying that’s the answer 🙂 But it sounds reasonnable. In your case, the problem would come from VLR/HLR rather than the MS.
    MS repeats the LU REQ because the previous ones didn’t get through.

    If you are lucky enough to trace your situation, let me know !!

    #66527 Reply

    Hi Pix,
    The SD congestion comes from Location Update. As the indicator I get from NPO, during the hour that problem happen, SD_assign_request increase from 100-200 (normal value) to 16.000, and most of them is SD_assign_request_lu.
    The problem happen almost everynight, in different BSCs,especially all the cells that have the problem are in the border of the LAC. I found in some cases, the neighbor cells( different LAC) are loss of all channel. But in some cases, no. Especially there’s a case that the cell have problem are all in the border of the country.
    Noted that the problem happen only in 1 hour and disappear.

    #66528 Reply

    I’m also facing the SDCCH congestion problem (ALU network)as facing by Blackhole especially during midnight at LAC and country boarder due to location update.This is not causing by periodic LU because after we change the T3212 value there is no impact.Can anyone help us?

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