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High SD Drop – GEMINI Cells

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  • #67476 Reply
    Finsih
    Guest

    Hi All,

    I am having a high SD Drop rate rate in GEMINI Cells of Flexi BSC . The main reason is SDCCH_RADIO_FAIL . These cells doesnt have TCH Drops . The T200S was 780ms I changed it to 1260ms and found no improvement . The T3101 is 3s .

    #67477 Reply
    pix
    Guest

    hi finsih,

    I don’t know the specifics of the Gemeni cells, but the symptoms you are describing lead me to think that the problem is localized only on the TRX that carries the SDCCH timeslot, and not on the TRX that carries most of the TCH traffic.
    For example, in a cell with 2 trx, only one TS is configured as SDCCH, and it is located on TRX1. On the other hand, the TRX2 is the one which is “preferred” when it comes to carry TCH traffic.
    So you have to look at which frequency is used by TRX1, and ensured it is not interfered.
    Then check the path balance of TRX1, compared to the Path Balance of TRX2.
    And then, if you don’t find anything suspect, lock TRX2. Doing this will push the TCH traffic on TRX1. And there you should see that TCH also are getting drops!
    You can further confirm this by doing a drivetest.
    If TCH drop % does not increase after locking TRX2, then it means that it is perhaps an issue that comes from a MS / NSS problem. It seems that the Location Update procedure is not correctly handled by some MS on the market nowadays. As a result, every time such MS sends a LU, the SDCCH will be seized for more than 10s and then it will drop. I forgot what’s happening exactly. But one way to diagnose this is to prevent LU in the cell by setting the parameter “ATT” (=IMSI_ATTACH) to disable. After doing that you might see a decrease of SDCCH Drop %. If that’s the case, then it means there are “crazy” MS in this cell. You should therefore turn the ATT parameter back to “enable”. And trace the A-interface to detect which IMSI is going crazy. Then change the MS of this customer…

    Woow, what a long post…

    Cheers
    pix

    #67478 Reply
    Finsih
    Guest

    Hi PIX,

    Many thanks for the info . I will apply the recommendations from you .

    GEMINI , its an interface which we install in a Siemens BTS to make it suitable to support NSN FLEXI BSC . Here we had a Siemens network and we swapped the SIEMENS BSC to FLEXI BSC keeping the Siemens BTS .

    The problem is that in the Siemens Network they had the same no. of TRX and SD Config but they didn’t had SD Drops . So when the BSC swapped from Siemens to Flexi , then the SD Drop increased . The cells with high SD Drops mainly come in the BSC Boundary(FLEXI-SIEMNS Boundary) but these cells doesn’t have LU Failures in reports .

    Anyway I a going to follow your recommendations

    #67479 Reply
    jack
    Guest

    hi finish.
    i have a lot of HO Failure in gemini sites also.
    The T200S was 800ms I changed it to 1260ms and found no improvement . The T3101 is 3s .
    HO Failure include inracell and intercell HO.
    i activate SYNC parameer b/w cells of same site but no improvement.
    in DT i see that MS send HO complete to BTS but after that (in destination cell) MS send 2 empty measurement report and after that HO failure and MS back to old channel!!
    i dont have KPI to check it exactly.
    please guide me about that.

    #67480 Reply
    jack
    Guest

    i forget to say that HO failure happen with cause:N200+1 timeot(observe in DT logs)

    #67481 Reply
    piongly
    Guest

    Hi
    I just only want to take the ball to ask info on GEMINI feature

    with gemini:
    The BTS will remain Siemens (BS240 for istance) this bts is normally controlled by BR10 sw in BSC siemens

    if you change bsc and use flexi nsn you will use S14(Rg10) sw in bsc this could be a problem ?
    The parameters set is different between br10 and s14 so how all will work ?
    thx

    Some

    #67482 Reply
    jack
    Guest

    dear Finsih .
    are you resolve SD drops in gemini cells?
    please clarify us about this issue.
    thanks a lot

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