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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
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…. etci 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.
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
any feedback from NOKIA engineers about this?
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.
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.
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
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 SuccessAnd SDCCH Drop without LU could be;
Total SDCCH Drops – SDCCH Drop Due to LUcould be? or too easy :))
LU success could be get only for BSC base i think, not cell base i think, right?
Thanks for all comments, but all not given the response, how to solve those Drop due to T3101 expiry.
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
Hi all i can not find problem, please help me,
All sites and all BSCs have SDCCH drop due to ABIS failurebr
anvar
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