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Huge SCDDH Drop & Low CSSR

Viewing 15 posts - 1 through 15 (of 15 total)
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  • #58438 Reply
    User_2010
    Guest

    Hi Guys
    In one cell of site has huge SDCCH Drop rate (40-50%) and low CSSR (70-80%).
    This site is Nokia. Also no any alarm on this site due to NetAct software. No congestion.
    But what can be reasons for this problem? Could you help me?

    Thanks in advance.

    #58439 Reply
    FAZLI-AFGHAN
    Guest

    DEAR,
    THE REAS0N CAN BE INTERFERENCE, 0VERSH00T, MISSED NEIGHB0R,TX LINK STABILITY, CHECK THE NEIGHB0RING CELLS, THEY MAY BE D0WN.

    #58440 Reply
    User_2010
    Guest

    I have changed frequency, but it is the same.
    also checked neighbours, all of them are ok
    transmission also
    ???

    #58441 Reply
    Vickey
    Guest

    It mighy be the issue with the radio having SDCCH TS try to shift your SDCCH to other Radios form there current radio defination.

    #58442 Reply
    Vanderley
    Guest

    Hi User_2010
    In Nokia they have a very stupid formula for SDCCH drop.
    Check if in your formulas the counter SDCCH_Abis_fail_call is included. In most of the cases it counts so called phantom RACH.

    #58443 Reply
    User_2010
    Guest

    Hi Vanderley
    The formula is:

    SDCCH Drop Ratio =
    sum(sdcch_radio_fail+sdcch_rf_old_ho+sdcch_user_act+sdcch_bcsu_reset+ sdcch_netw_act+sdcch_abis_fail_call+sdcch_abis_fail_old+sdcch_bts_fail+ sdcch_lapd_fail+sdcch_a_if_fail_call+sdcch_a_if_fail_old) / sum(sdcch_assign+sdcch_ho_seiz)

    So if SDCCH_Abis_Fail included, what does it mean in this case?
    What can be the reason of the problem?

    Thanks in advance.

    #58444 Reply
    Vanderley
    Guest

    Hi,

    For me this is not a drop.
    This counter works when you receive on rach request with valid cause, you assign a SDCCH, no MS appear on channel in certain time (i don’t remember the exact timer value), and the channel is released with this cause. This counter is on ABIS that’s why they called it Abis fail.
    No one could tell if this is really a MS. Also why drop if you never get on the channel.
    Look at Nokia explanation
    Phantoms affect SDCCH_abis_fail_*
    SDCCH drop ratio counts the ratio of all SDCCH failures to SDCCH seizures.
    Normally most of the seizures are caused because of phantoms which are counted as SDCCH_abis_fail_call and SDCCH_abis_fail_old. In practice, the latter case does not practically occur because SDCCH handovers are usually not
    used and particularly because phantoms do not perform handover.
    The percentage of SDCCH_abis_fail_call used to be very high in a low traffic
    network (even tens of per cent) whereas in a high traffic network the percentage settled down to around 18-20 per cent. In BTS B9, BTS RACH detection was improved, and figures well under 10 per cent are now typical.

    #58445 Reply
    Hosea
    Guest

    Hi Vanderley, I also have the same symptoms on my network like the ones explained by User_2010, but I checked the formula and it doesn’t contain SDCCH_Abis_fail_call in it. Here is the formula used.

    100*sum(sdcch_radio_fail+sdcch_rf_old_ho+sdcch_user_act+sdcch_netw_act+sdcch_bcsu_reset+sdcch_bts_fail+sdcch_lapd_fail)/sum(sdcch_assign BSC Traffic+sdcch_ho_seiz).

    can you please help?

    #58446 Reply
    ATTO
    Guest

    Hi User_2010 , I usually got this problem with Alcatel. What i do is to check for SDCCH Mean holding time for all of the TRXs ( of course if u’ve got more than One). U could probably see that one TRX have huge SD MHT , then switch off the SDCCH defined on that TRX , you should overcome SD drops. And this TRX might be the cause of your low CSSR because of TCH assignment failures radio. Just try theses , and feedback .

    I hope it would help u.

    #58447 Reply
    User_2010
    Guest

    Hi Atto
    I have changed SDCCH location from BCCH TRX to another one. But it didn’t help. Problem are same.
    Now I have found a problem on this site, maybe reason is this

    “RSSI detected Rxsignal difference exceeding threshold”

    Realy, I don’t know its explanation.
    Also pay attention that the site is Nokia.

    Thanks

    #58448 Reply
    ATTO
    Guest

    hi User_2010,

    i know u’re using NOKIA, it is why i didn’t give you KPI names to check.
    Just try to have KPI per TRX, it is the best solution for finding ur problem.
    U said u have change SDCCH location from the BCCH TRX to another TRX; What is your config, i mean how many SDCCH did you define on this cell?

    “RSSI detected Rxsignal difference exceeding threshold” i don’t know what it means , i’m not using NOKIA , but you should probably got a path unbalanced, look for HO causes and see if ur HO are due to low Uplink level or uplink quality too bad.

    Thanks.

    #58449 Reply
    Vanderley
    Guest

    Hi User_2010,
    ATTO is right – check you HW first.
    Also if you use dynamic SDCCH and it is used (a lot of SD traffic) then keep in mind that it is always from the TRX that have less or no static SD configured

    #58450 Reply
    Shailendra singh
    Guest

    Hi,
    I want to know about immediate assignment in the call set up,
    I mean wht is the role and how and when it works.

    #58451 Reply
    conye
    Guest

    try to transfer your sddch on other timeslot on the same trx

    #58452 Reply
    Collins
    Guest

    Trx Imbalance causing low CSSR

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