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Viewing 15 posts - 1 through 15 (of 99 total)
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  • #35710

    Could you tell me what are all the actions to be taken to reduce SDCCH drops?


    Check SDCCH MHT if this one exceeds 3,5 sec , check TCH blocking. Check related counters of SDCCH drop example due to ABIS, RF , A-interface etc.
    Most common case is interference.


    Hi guys,

    I just found about this forum and I think this is really useful! I am an RF engineer working for an operator using Nokia BSS and we have a site that is having many SDCCH drops (around 60%) on a LAC change border with 2 TRX. It used to work fine until 1 month ago.

    We have alarm 7745 CHANNEL FAILURE RATE ABOVE DEFINED THRESHOLD but we have checked both TRX with a loop test and they seem to work properly, we changed SDCCHs from one TRX to another without any improvement.

    We have checked interferences, cables, masses and Baseband cards but it has not improved.

    Do you have any ideas what the problem could be and how to solve it?

    thanks very much in advance!


    It suddenly happened that the SDCCH drop rate increased ? Did you change frequencies or the antenna design ?

    When something like this happens (and I didn’t change anything on the site), I usually suspect a hardware problem.
    Try resetting the Abis link, the TRXs, etc…

    Then you can try to change the frequencies of the cell, and eventually go drive-test around this area.

    As said ealier, check the Mean Holding Time (MHT). What is it’s vallue ? What about the TCH assignment success rate ? The Call drop rate ? The TCH MHT ?

    Good luck Silvia, let us know how it goes…


    Hi Pix,

    the SDCCH drop rate increased all of a sudden and we did not change the antennas nor the frequencies, that is why we also suspect it is a HW problem but still could not find it.

    The SDCCH MHT is around 9.5 but the site is on a LAC border change and we think this is due to the Location updates, not related to this SDCCH drop rate.

    Thanks for the advice


    Hi Silvia,

    Even on a LAC border, the “SDCCH mht” will never reach 9.5 seconds. It’s way too much !

    Does this cell handle a lot of traffic (TCH) or not ? If yes, then I advise you change the TRX’s or the cell combiner.

    If you feel it is not a HW problem, then you can try increasing the Cell Reselection Hysteresis between both LACs, and increase the anti pingpong reselect timer. But in my opinion, you cell has a HW problem. Have you performed a drivetest on it ? what about other QoS indicators ?

    RF Learner


    ur site is on LA border,

    wat kind of signalling u r using.

    let me know i will try to help.

    my email ID is



    Wht are hte reasons of SD drop, i-e suddenly lost or Low SS UL/DL or bad qulity DL. Can u see these in ur system.


    The reason for SD drop is cochannel interference usually.Check your frequency plan


    Hi I am working with a company that utilizes Nortel Products and we have a couple of Dual Band sites i.e. 1900 and 850 MHz. I noticed that at a certain time in the night there is a sharp increase in SDCCH Failed Assignment Rates one of the 1900 sectors on a particular site.

    Please Advise.


    what is differnce between sd drop and sdcch blocking.plz explaine .


    SD DROP = SDCCH DROP = drop during a sdcch phase (for call assignment for instance)
    SDCCH BLOCKING = SDCCH assignment rejected because all the SDCCH timeslots are busy (= congestion)


    which parameter depend on sdcch drop.

    fresh engineer

    what is the relation between lac and sdcch…plz explain it to me…am a fresh engineer



    when a subscriber changes LAC, its mobile will trigger a location update procedure. This procedure takes place on the SDCCH channel.
    – too many LACs will increase the amount of load on the SDCCH channels of the cells at LAC borders. This can lead to SDCCH congestion on the border cells, but also overload the BSC.
    – locating a LAC border in an area where a lot of people are moving in and out, it will generate additional Location Update procedures.
    – not enough LACs, meaning the size of a LAC is large, this might create paging problem : the subscribers locations is known at the LAC resolution, so when receiving a call, the MSC as to page for the whole LAC. Too many subs in a LAC : too many Pagings.


Viewing 15 posts - 1 through 15 (of 99 total)
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