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I’m suddenly facing a high SDCCH Drop (50%) for a site located at a frontier between 2 countries. The TCH drop is low, the LU request is high but success low (45%). I ‘ve change the BCCH frequencies on which SDCCH is located without success. I’m suspected a problem related with LU but I can’t explain why this high drop on SDCCH (at least congestion would be comprehensible).
Thanks
Do you know what happens when a foreign MS attempts to connect to your network ? Perhaps the location update is rejected, but without the proper msg on the air interface.
So the MS still waits for an answer until there’s a drop..
you could check the average duration of the sdcch, if it’s higher than before ?otherwise, try putting more “tch preference” priority on the TRX that carries the SDCCH timeslot, so that more calls are established on this TRX.
If call drop increases, then it’s a problem related to the radio of this TRX.
If the call drop is stable and traffic is succesfully handled by the “sdcch trx” , then the problem is indeed on the signalling part.Thank you Pix, for your response.
I don’t Know what happens for foreign MS. Notice that a new roaming agreement was made with a foreign operator few days before the trouble. But I’m not sure that MS from this operator roam in the concerned area(it’s a new operator and this border area is far from the main towns).
The site is a S112 and the problem is more serious for the one TRX sectors. For them there is no need to set a priority they carry the sdcch.
I give you some statistics, that could help for further analysis. The comparison is made between two date, before and after the problem.
Random access attempt:
369257 vs 441223Random access success:
23,17 vs 58,2 (increase during the problem)SDCCH:
seizure attempts:85623 vs 255732
congestion(%):0.16 vs 26.33
time congestion(%):0.03 vs 7.03
success at seizure(%):81.58vs55.02
drop(%): 6.17 vs 45.77
mean holding time:6.29s vs 11.15sLOCATION UPDATE:
attempts:80800 vs 247715
success(%): 83.99 vs 33.38The site is located on a remote BSC and is not at my location, so I’m not able to make abis traces and drive test, but if the cause cannot be find without I’ll go there.
Thanks
Dear PIX.
i put my SDCCH & TCH on time slot properly.where in one time slot One SDCCH and & 7 TCH.
Some site i hv 2/2/2 confg, some 4/4/3 confg.
So..how its happend SDCCH drop rate high.
Hi all,
in one site we increased capacity in signaling, per one sdcch cell2 and cell3. In cell1 we didn’t add sdcch. From that moment sdcch drop increased at cell1. Why? There is no interference, HW OK…
Waiting for your help!
Best Regards,
Rex.Anyone?
Rex,
Sorry, I don’t have an answer. What about the sd drop in the cell 2 and cell 3 ?
What are the actual values of sd drops before and after ? (rate and number of drops, please)
As a workaround, have you tried resetting the TRX and the TCU ?
My first thought is regarding the TCU and RSL capacity : perhaps there is too much signalling now, leading to drops.
You could check the LapD congestion (thanks to counter L1.18, counter type 7)Also, to isolate the problem : try removing the extra SDCCH on cells 2 & 3. See if it reverts to the initial values.
Cheers,
pixHi Pix,
thanks for your reply, as allways. Before adding sdcch in the cell 2 and 3, the drop was around 0.60%, after over 5% (about 70-80 drops per hour). Interesting is that sdcch_assignment_failure decreased and sdcch_drop increased at the moment of adding extra sdcch. Of course,we tried to reset corresponding TRX and TCU, still the same. Today we removed extra sdcch at the end of the day, will see tomorow the results. I’ll inform you tomorow about that. Counter type 7 is not activated, and cannot see the LapD congestion.
Thanks again,
Regards,
RexGuys,
May i know the different reasons for SD Block and SDCCH Drop?
Hi,
after removing extra sdcch, there were no improvments. We reset again TRXs and TCUCs and it seems drop started to decrease.Hi,
Well, it should decrease immediately back to the first values (the good ones).
This problem appears sometimes, in some BTS. The fix is just to reset the TRX. I hope they’ll solve this in the new release.Regards,
pixHi,
In RNO I can’t see counter type 7 (LAPD measureent). Type 7 wasn’t enabled in PMC. We tried to enable just for one BSC for a couple of hours as On Demand PMC (ODPMC). What should I do to see that in RNO?
Thanks,
Rexyou can enable it permanently, don’t worry 🙂
i’ll check where it can be seen, but i bellieve you can see it in RNO along with all other counters. Have you checked BTS objects ?
I’ll tell you tomorrow.Cheers,
pixHi Pix,
I checked BTS objects, there is no counter type 7. The only counters available are CUMULATED_TIME_FREE_EXTRA_BONUS_ABIS_NIBBLES (P472) and MIN_NB_FREE_EXTRA_BONUS_ABIS_NIBBLE (P484).
BR,
RexPix?
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