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Nokia SDCCH Drop Rate due to Abis

Viewing 11 posts - 1 through 11 (of 11 total)
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  • #67247 Reply
    caki
    Guest

    Hello all,
    One of our vendor is NSN and SDCCH Drop rate is around 1-1.5 % for most of cells and big part of reason seem as Abis failure, around 80 % and Radio Fail is 20 %.

    At first I think, it could be due to frq plan, overshooting or any rf related reason..

    But its not weird that all cells with SDCCH drop more than 1 %?

    when we check the reason of Abis Fail, ghost rach coming up which we cant seperate them i think.

    anythingelse?

    thanks

    #67248 Reply
    Alonewolves
    Guest

    Hello caki,

    we use 2g NSN network too , and SDCCH drop rate for a few sector extremely high.

    NSN support team suggested to :

    1- Check whether Abis interface is stable using PA.
    2- Add another SDCCH channel to the TRX suffering from SDCCH drop
    3- Change TS of SDDCH to another TS in TRX
    4- Replace BB2 & TRX with new ones
    5- Change connector & Cable and even antenna if SDCCH drop continues.
    6- Measure interferance,
    7- ensure that there is no POWER issue in the site, ( DC power fluctuation)
    8- Poor Coverage issue, may be the reason…. etc

    i have observed that SDDCH drop as you mentioned it is related to Abis failure
    Main reason in Abis Fialure is T3101 timer expiry,
    i don’t know how to improve T3101 timer expiry situation ,
    if you have any idea , pls share it with us ,

    Regards.

    #67249 Reply
    caki
    Guest

    thanks Alonewolves,

    we can consider all problem you mentioned, but I think it should be something common for all cells in NOKIA region. Because there are few cells with SD drop below 1 %. Thats why I suspect from counter/formula or something more common..

    ps. we use sdr_4 formula

    there may be another formula to discard Phantom RACH and bad impact on Abis fail counter..

    For example, whats avg SD Drop in other Nokia network? if its around 1-1.5 % like we have, it’d be common NSN problem

    #67250 Reply
    caki
    Guest

    any feedback from NOKIA engineers about this?

    #67251 Reply
    Alonewolves
    Guest

    hello caki,

    i will feedback your problem with my limited knowledge on radio part.

    Phantom or Ghost RACH result T3101 expiry ,
    then it triggers abis_fail_call and increase this counter by 1,

    here is the formula you mentioned.

    sum(a.sdcch_radio_fail
    + a.sdcch_rf_old_ho
    + a.sdcch_user_act
    + a.sdcch_bcsu_reset
    + a.sdcch_netw_act
    + a.sdcch_abis_fail_call
    + a.sdcch_abis_fail_old
    + a.sdcch_bts_fail
    + a.sdcch_lapd_fail
    + a.sdcch_a_if_fail_call
    + a.sdcch_a_if_fail_old
    – b. T3101_EXPIRED)
    100 * ——————————–
    sum(sdcch_assign+sdcch_ho_seiz)

    a = RBS_PS_TRAFFIC_{OBJ_AGG}_{TIME_AGG}
    b = RBS_PS_SERVICE_{OBJ_AGG}_{TIME_AGG}

    according to SDR_4 formula, Ghost & Phantom impact already subtracted.

    in our network just i have check , majority of sectors have sdr_4 rate below %2 , but a few sectors has more than %10,

    by the way, i think you are able to apply your formula and track your KPI using builging Report module in Netact.

    Pls correct me if i am wrong, bcs i am new in radio part.

    #67252 Reply
    caki
    Guest

    Hi Alonewolves,

    you mean t3101 trigger only for ghost rach? I dont think so

    it should be pegged for all abis related problem and so timer expiry, not only for ghost rach i guess..

    About formula, we use same formula and agai ghost rach not discarded here. I pasted some info from google, check it out, its quite clear ha

    Short info for t3101:
    T3101 (Default 3s)

    When: immediate assignment process

    Timer T3101 is used to set the interval between the start time when an IMM ASS message is sent by BSC and the stop time when an EST IND message is reported to BSC. BSC releases the seized SDCCH if no EST IND message is received within the time specified by timer T3101.

    Normal flow

    MS → RACH → BSC

    MS ← IMM ASS ← BSC (start counting the timer)

    MS → EST IND → BSC (stop the timer)

    Abnormal flow

    1). MS → RACH → BSC

    MS X IMM ASS ← BSC (start counting the timer)

    In this case IMM ASS message is not received by the MS. Then BSC will release the seized SDCCH after waiting the time specified by timer T3101.

    2). MS → RACH → BSC

    MS ← IMM ASS ← BSC (start counting the timer)

    MS X EST IND X BSC

    In this case, ESTIND message is not sent by the MS after receiving IMM ASS message. The BSC will release seized SDCCH channel as above case.

    3). MS → RACH → BSC

    MS ← IMM ASS ← BSC (start counting the timer)

    MS → EST IND X BSC

    In this case ESTIND message is sent by MS. But BSC does not receive ESTIND message. The seized SDCCH channel will release as above cases.

    #67253 Reply
    caki
    Guest

    hello again,

    maybe NOKIA eng will help us on this.

    Is it possible to calculate SDCCH Drop rate without Location Update??

    Because its not possible to seperate SD drops for Call/LU in SDCCH_Radio_Fail & SDCCH_Abis_Fail counters.

    You may know another tricky way to split them

    thanks

    #67254 Reply
    timroy
    Guest

    caki,
    we have same SD Drop problems too, it will be good to seperate them if possible but i dont know,

    Maybe possible to get NUmber of Successfull Location update and then;

    SDCCH Drop Due to LU will be;
    LU Attempt – LU Success

    And SDCCH Drop without LU could be;
    Total SDCCH Drops – SDCCH Drop Due to LU

    could be? or too easy :))

    LU success could be get only for BSC base i think, not cell base i think, right?

    #67255 Reply
    silex
    Guest

    Thanks for all comments, but all not given the response, how to solve those Drop due to T3101 expiry.

    #67256 Reply
    Mehrdad
    Guest

    Hi Caki,

    I am familiar with this issue in Nokia system for more than 5 years. SDCCH Drop Rate near to 1-1.5% is usual in NSN. I worked in 2 operators of my country that is using NSN BSS and the average value of SDCCH Drop rate is 1.5% both operators.

    After several analysis we are using below formula now; SDCCH_ABIS_FAIL_CALL removed from nominator and SDCCH_ASSIGN_57 is being used in denominator; SDCCH Drop value decreaed about 0.5% after this change:

    100 * ((SDCCH_RADIO_FAIL + SDCCH_RF_OLD_HO + SDCCH_USER_ACT + SDCCH_BCSU_RESET + SDCCH_NETW_ACT +
    SDCCH_BTS_FAIL + SDCCH_LAPD_FAIL + SDCCH_A_IF_FAIL_CALL + SDCCH_A_IF_FAIL_OLD + SDCCH_ABIS_FAIL_OLD)/
    (SDCCH_ASSIGN_57 + SDCCH_HO_SEIZ))

    BR – Mehrdad

    #67257 Reply
    Anvar
    Guest

    Hi all i can not find problem, please help me,
    All sites and all BSCs have SDCCH drop due to ABIS failure

    br
    anvar

Viewing 11 posts - 1 through 11 (of 11 total)
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