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GOS vs. TCH assignment failure? ASAYC!!!

Viewing 15 posts - 16 through 30 (of 53 total)
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  • #51918



    Hi every body ,
    My job includes solving GSM BTS and BSC problems .
    I am facing this problem of assignment failure in some sectors of the BTS installed in our network.Also in some sectors number of calls attemted is very small as compared to other sectors though all the sectors are equally populated.
    As I am new to GSM systems ,will anybody help me please to solve these two problems.
    Pix ,can you help me please ?
    How should be my approach to gather knowledge to solve BTS,BSC problems,can anybody suggest please?



    In order to learn, you have to work with experienced engineers, you’ll certainly pick up some methods from them.

    You can also read books about GSM + GSM algorithms explanations from your vendor.

    Now, regarding your problem, in my opinion, this is not really a problem if there is less call requests in one cell compared to another cell.
    Even if you believe the amount of people in the covered area of each sector is the same, it might not be correct. You can’t know for sure : maybe the low populated cell has a coverage which is small, because there is actually another neighbor cell that also covers this area.

    You have to check the number of SDCCH requests, the number of TCH requests and the number of TCH succesfully allocated.
    If the nb of sdcch requests is low, it means you don’t have much subscribers in this area.


    Thanks very much pix.
    In some sectors number of calls are abnormally lower.
    Anyway I will check it ,will let you know.
    Thanks again.


    what are causes of assignment failure ? remedial measures ?Can anyone explain ? Pix, can you help please ?


    Hi all,
    I am working for GSM network, specifically for Pico BTS (indoor solution). Some BTS’s are facing TCH assigment failure problem. I would like to know what is the cause of this issue and where i can good information to learn more about KPIs. Last week i got another problem with SDCCH real blocking i saw at the level counter that the counter that was increased was sdcch_abis_fail_call
    . I would like to know what i do need to check?
    Thx in advance for the support.


    what is GOS?


    Pix, can you help please ?


    Jorhqt, You can also check the number of subscribers localised on the different cells.
    Also, are both cells getting trafic normally that is both by assignment and Handover


    Assignment failures could be due to radio: that is bad frequency planning. In this case, you generally have quality problems as well.
    They could also be due to hardware problems like a faulty TRX. This can be detected by checking the QOS per TRX.

    If the problem started without any frequency or other radio parameter changes, there is a high probability that this is a hardware problem.



    pix has already explained when TCH Assignment Failures occure:

    “TCH assignment is the phase during call setup when the BSS wants to shift the MS from SDCCH to TCH.

    The TCH assignment is divided in 2 parts :

    1- the BSS checks that a timeslot TCH is available in the serving cell (or in neighbor cells, with directed retry)

    2- the BSS asks the MS to move onto the TCH timeslot and to send an initial confirmation message while on this TCH timeslot.

    In part 1 : there is a TCH REQUEST, which leads to a TCH ALLOCATED (= available TCH) or a TCH REJECTED (= no TCH availble)

    In part 2 : the MS will try to access this TCH. If the dialog BTS/MS onto this TCH is possible, this is a TCH SUCCESS. If the dialog is not possible, this is a TCH FAILURE.

    The TCH CONGESTION occurs only in phase 1.
    The TCH FAILURE occurs only in phase 2 (with most common problems such as RADIO or HARDWARE PROBLEMS)”

    For example, if you have a cell with BCCH on P-GSM band and TCH on E-GSM band, and you make a call via repeater that doesn’t support E-GSM band. During call setup, you get SDCCH on P-GSM frequency, and BSS gives you a TCH on E-GSM frequency. Since repeater doesn’t support E-GSM, you won’t be able to continue communication on allocated TCH (since you have to low RxLev on E-GSM TCH, for example RxLevBCCH(P-GSM)=-90 dBm and RxLevTCH(E-GSM)=-115 dBm). If TRX is faulty, you could get the same message. Probably very strong interference on that TCH would lead to the same.


    Hello anybody can help what causes SDCCH drop? and how to solve it.


    Hi all,
    Can I have explaination on the MHT (mean holding time). Why Mean?


    Hi All,
    I ‘am using business object for performance counters setup.
    When try to open BO I receive this fault: CS
    DBDriver failed to load : C:\Program Files\Business Objects\BusinessObjects Enterprise 6\dataAccess\RDBMS\connectionServer\dbd_ctlib.dll (Specific module is not found.)

    Someone can help me?


    I am working with a GSM company as Optimization supervisor and we have 30 % congestion in the network and that is showing some thing wrong how can make a report from the counters regarding,

Viewing 15 posts - 16 through 30 (of 53 total)
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