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T3101 Timer expiry

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  • #67234

    i noticed that number of T3101 timer expires in a specific sector more than other sectors,

    number of T3101 expiry in the sector is 1151, on the other hand for other sectors in network
    at most 110,

    could you please tell me what could be the reason ? .
    is it Antenna Faulty ?

    Thanks for advance…


    Hello experts,

    i am going to simplify my question :

    There is a huge differences about T3101 expiry between a specific sector and rest of the other sectors in network ?

    what could be the reasons ?




    for info :

    it’s probably a coverage or interference problem, or a hardware failure on the TRX that carries one of the SDCCH. Indeed T3101 expires because the MS cannot enter on the SDCCH TS of this TRX.



    hi Pix , Thanks for Answer…

    a hardware failure on the TRX that carries one of the SDCCH –> That is right , i have changed SDCCH to another TS..

    Let me why i ask this question :
    you may contribute the problem more.

    one of our network is 2G NSN network & we face 7745 CHANNEL FAILURE RATE ABOVE DEFINED THRESHOLD too much , 10 times or more daily ,

    NSN support contract has been expired for us so i investigate this alarm on internet to find out a solution.

    Accourding to Alarm if SDCCH Channel failure is more that %80 percent during 60 munites , network generates this alarm.

    finally i observed that SDDCH drop rate high cells generate this alarm,

    SDCCH drop rate is high because due to radio failure + due to Abis Failure , Other reasons are approximately zero effect when i check the SDDCH Report ( example : due to A failure, Due to Handover Faiure, illegal est. cause. LAPD failue, Network config. change, BSCU restart…etc no affect on SDDCH drop ) ..

    So Due to Abis Failue is major impact on SDCCH drop in my network.

    i have focused on Sdcch_abis_fail_call then…

    Major impact on sdcch_abis_call is T3101 timer expiry,

    some reasons why T3101 expries are Ghost access & Timing advance
    & interferance.

    interference level & Ghost Access a few through the network.

    but i am going to check Timing advance level in sectors today.

    My question what should i do more , what do you advise me to do ?

    Thanks and best



    having a sdcch channel fail % above 80% cannot be due to :
    – coverage
    – interference
    – ghost rach (except when very low traffic)

    IMO you have to focus on the hardware !
    I don’t understand why they put the name “Abis” in Sdcch_abis_fail_call. Expiry of T3101 has very little to do with Abis ! Except, perhaps, congestion of the “radio signalling link” of this trx on the abis. Is this “RSL” congested ?

    So hardware problem = you have to fix the BTS. By stopping frequency hopping (if activated) and changing the position of the SDCCH timeslot to another TRX, the problem should disappear. If not, try to put all SDCCH timeslots on the TRX BCCH only.

    Then, let’s see what happens…
    possible problems : faulty trx, crossed feeders or crossed mains…?



    experts can u give me simple answer for this question.

    when is the TBF is aborted?


    Thanks a lot Pix.
    i am going to check radio signalling link utilization as well.
    if i would’t see any problem, i perform :

    1. stop frequency hopping then check the SDCCH Failure rate
    2. if continues , shift sdcch positon to next TS
    3. if continues signaling card and TRX Harware replacement
    4. if still continues checking whether cables are corrosed
    5.if still continues, Jumper cable, feeder, connector finally Antenna replacement.

    Best Regard Pix.
    Thanks spending time for answer


    A small suggestion
    Pls check C-BSIC-BCCH in immediate vicinity.I hope this has already been checked,but still,in case.



    Thanks bijoy for your suggestion.


    To improve SDCCH Call Drop and Failures.

    There are several steps u can do before replacing the HW on the site.

    – SDCCH failures can be caused by malfunction UE’s that don’t answer.
    (this problem is very hard to get because u need to find the specific IMSI which is causing and then call the client).
    To improve statistics I prefer to do :
    – Add one more SDCCH channel on the seccond TRX on the cell, switch the priorities for allocation SDCCH.
    – Change frequencies on BCCH.
    – Try to move the failures to another cell like changing the Cell Reselection Offset of the sector so that the problem appears in the neighbor cell the problem is not from the HW.
    – Try to check what are the levels for the failures if there is possibility to trace it and change the tilts of the sector if is a overshooter. If it is hard to make tilt changes, then reduce the power.

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