- This topic has 14 replies, 1 voice, and was last updated 9 years, 6 months ago by Collins.
14th August 2009 at 06:53 #58438User_2010Guest
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.14th August 2009 at 07:38 #58439FAZLI-AFGHANGuest
THE REAS0N CAN BE INTERFERENCE, 0VERSH00T, MISSED NEIGHB0R,TX LINK STABILITY, CHECK THE NEIGHB0RING CELLS, THEY MAY BE D0WN.14th August 2009 at 10:03 #58440User_2010Guest
I have changed frequency, but it is the same.
also checked neighbours, all of them are ok
???15th August 2009 at 11:18 #58441VickeyGuest
It mighy be the issue with the radio having SDCCH TS try to shift your SDCCH to other Radios form there current radio defination.17th August 2009 at 15:38 #58442VanderleyGuest
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.18th August 2009 at 04:20 #58443User_2010Guest
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.18th August 2009 at 07:05 #58444VanderleyGuest
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.20th August 2009 at 11:28 #58445HoseaGuest
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?20th August 2009 at 16:27 #58446ATTOGuest
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.21st August 2009 at 07:04 #58447User_2010Guest
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.
Thanks21st August 2009 at 08:57 #58448ATTOGuest
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.24th August 2009 at 17:13 #58449VanderleyGuest
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 configured25th August 2009 at 13:20 #58450Shailendra singhGuest
I want to know about immediate assignment in the call set up,
I mean wht is the role and how and when it works.19th September 2009 at 18:49 #58451conyeGuest
try to transfer your sddch on other timeslot on the same trx9th March 2011 at 09:00 #58452CollinsGuest
Trx Imbalance causing low CSSR