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SDCCH huge congestion

Viewing 8 posts - 1 through 8 (of 8 total)
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  • #50754 Reply
    Dux
    Guest

    We saw a huge increase in SDCCH congestion in a 15 min period at 1am. Yesterday no congestion in sites but today we saw SDCCH requests jump to 37000-50000 on different cells in different towns.
    After one 15 min period everything returned to normal but throws statistics through the roof for whole day.

    Question, Does anyone know what would have caused such an increase in SDCCH requests, there were no traffic channels requested and no SMS traffic?

    #50755 Reply
    Abdel
    Guest

    Hi dux,

    Can you check whether the LAI of the neighbouring cells are the same if not then it will generate a lot of location update, plus authentication, and IMEI checking this is a great deal of signalling flow generated by the Subscribers who entered that cells with the different LAI. There can be other reasons.

    #50756 Reply
    NK
    Guest

    Hi! Dux,

    Check also BTS is up after down for a certain period or not. Generally, MS performs LU if BTS is up after down for a certain period.

    regards,
    NK

    #50757 Reply
    Pix
    Guest

    As NK said, it certainly has to do with a massive amount of location updates (you can see perhaps that the SDCCH were allocated for LU ?)

    The main possibility is that at 1am one of your competitor operator had several BTS down, de to BSC outage, or Abis outage probably. At that point, all the subscribers of this operator will search for another network and probably select your cells. Once the BTS were up again, subscribers would gradually reselect automatically their home BTS (timer defined in MS).

    Another possibility is that your own subscribers performed a location update all at the same time. This can be due to (as NK said) some problem with the BTS (but i don’t really see how…) or at NSS level : the MSC asked many MS to perform a location update at the same time. Were there any MSC action last night ?

    Regards,
    Pix

    #50758 Reply
    Dux
    Guest

    No, no MSC activities but Pix you was right. It’s because of other operator. They lost BTSs at the same time
    in several different areas.
    Tnanks

    #50759 Reply
    TNS
    Guest

    Hi, Dux.
    In this case you have a national roaming, yes?

    Hi, Pix.
    “… This can be due to (as NK said) some problem with the BTS (but i don’t really see how…) …”.
    If in dense urban area we have one BTS down than nothing happen – all MSs will reselect the BTS following the reselection criterea.
    If we have some BTSs down ( or one in rural area ), so we have a MSs without coverage.
    In the moment of BTSs up there will be a large number of network registration procedures with all attended events…

    BR,
    TNS

    #50760 Reply
    Dux
    Guest

    Yes TNS

    #50761 Reply
    NK
    Guest

    Hi! Dux,Pix,TNS,

    During Traffic analysis, I found that SDCCH congestions were extremely high but voice traffic were low. When I checked radio command, the sites were down. This had happened in urban areas where we had a lot of cells. Even one cell was down, the neighbor cells used to serve that area without latching in external network.

    I do not understand why MS performs LU. But my MSC’s colleague told me that once site was down , MS performed LU when the BTS was UP again.

    We are using Siemens network.

    Regards,
    NK

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