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High SDCCH Assignment Failure

Kanchan Gupta - 7th March 2018  (08:07 GMT)

I have come across with similar case in Nokia.
voice CSSR (Phase 3 CSSR) is degrading in sec 2.
Multiple alarms like, BTS with no transactions, Object Administrative state changed BCCH missing, BTS O&M Link Failure, Configuration of BCF failed are pegging on site. SDCCH Phase 3 drops have been increased from same date on sec 2. No change in traffic pattern observed. No TCH/SDCCH Blocking observed. No IM/CM found corelated from the date of degradation. HOSR is degraded on sec-1 from same date. BCCH frequency swap has been done between the TRX5 & TRX 6 on same date. On checking TA pattern, sec B is serving till 6.05km, no change in TA pattern observed. Intersite distance is 5.4km and site is at BSC boundary. No frequency Clash, No LAC mismatch observed.

can anybody calrify me about Phase 3 CSSR degradation

pix - 12th October 2013  (14:15 GMT)

hi yalda,

Probably because the incoming random access request is not valid. Therefore the BSC will wait for an Immediate Assignment FOREVER, until the timer t3101 expires.

Whichever the value of t3101 you choose, the timer will always expire, for such "ghost rach". There is a high amount of ghost rach in E/ BTS, because it is extremely sensitive and does not filter the ul noise it receives. It tends to decode a lot of ghost rach. The positive aspect of this sensitivity is a bigger cell range.

In order to filter the ghost rach, we experimented quite succesfully with the MAXTA and TALIM values.
Try setting MAXTA=20 and TALIM=19 (or even lower MAXTA if you can afford it). This will successfully reduce the impact of ghost rach on your t3101 expiry counter (CESSTIMASS)


yalda - 12th October 2013  (10:52 GMT)

Can anybody help why T3101 tIMER in Ericsson system Expires although we increase the value of timer???

ng - 28th May 2012  (04:29 GMT)

hi in few cells sdcch assignment is very poor 80-90%, sdcch drops are high too, kindly suggest me to improve both

Rf Engineer - 29th August 2011  (12:23 GMT)

You can find good info SDCCH failure from below link.


where xx replaced by tt

Pix - 22nd July 2011  (14:36 GMT)


Probably a TCH Assignement Failure, either due to TCH congestion, due to Radio failure, or due to TRX failure.


Malay - 22nd July 2011  (06:56 GMT)

SDCCH assignment completed but Call is not established..Why??

Tejbir Rathi - 22nd July 2011  (03:43 GMT)


i want to know the name of that parameter by which we change the TRX Priority of tch in ericsson system.( TRP in nokia system.

abhi - 4th May 2011  (07:33 GMT)

how we get abis traces?

Manoj Kumar Singh - 21st February 2011  (05:30 GMT)

Handover is getting failed due better cell.

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