- This topic has 15 replies, 1 voice, and was last updated 12 years, 1 month ago by pix.
25th December 2008 at 18:53 #55209RachidGuest
we implement a common bcch feature in one site ( gsm900+dcs1800) and we got some problem with tch allocation failure during call& HO which register a huge degradation.
what could be the reason?
also is it possible to make a HO from a cell 900 of one segment to cell 1800 of another segment.
thanks25th December 2008 at 20:52 #55210EvgenGuest
For TCH reselection beetwen segments responsible HOC parameters LAR(NON BCCH LAYER ACCESS THRESHOLD) ,LER (NON BCCH LAYER EXIT THRESHOLD), and BTS parameter NBL (NON BCCH LAYER OFFSET). Usually LAR=-85, LER=-95, NBL=5,7. Also parameter NBL must be set only for non-BCCH segment layer, because in other case you will have 99% RACH reject on cell. For GPRS reselection between segmentson Common BCCH need tune GPU & GPL parameters.
Good luck.27th December 2008 at 17:54 #55211cpesGuest
if with these parametrs (LAR=-85, LER=-95, NBL=5,7) you will have big tch drops, increase NBL…27th December 2008 at 21:42 #55212EvgenGuest
Pls, you can explaine more deeply, which reason will for drops?
P.S. We have small TCDR value on this segments.29th December 2008 at 11:31 #55213PixGuest
Could you please state your vendor ?
The degradation could be due to the fact that all the dcs1800 resources are occupied (which is a good thing). Because all traffic is carried in this inner zone, you understand that you fully use the benefit of the DCS1800 band.
However, the BSC will still try to push more traffic in the inner zone, which leads to incoming HO congestion : HO from outer zone or from neighbor cells towards the inner zone cannot be done because no resources are available.
This is not a problem 🙂 You have two possibilities :
1/ share the traffic equally between GSM900 zone and DCS1800 zone. Bad option in my opinion, because you should load the inner zone as much as possible.
2/ stop watching the (HO + normal assignment) congestion rate, but watch only the (normal assignment) congestion rate. You will have a much better view of what is the real QoS in this cell.
pix30th December 2008 at 09:41 #55214RachidGuest
my vendor is Nokia.
just one thing, there is no tch blocking in that segment. but high Tch Activation Failure either in Assignment or Handover.
Thanks31st December 2008 at 17:29 #55215PixGuest
Thx for the details rachid,
Well, I’m not a nokia expert, but perhaps you should check your parameters : it’s possible that you push MS too much in the inner segment ? MS will suffer poor RXLEV, and fail to seize the TCH.
Second possibility, which happen a lot in case of dualband cells : swap feeders… the inner segment of cell A is actually transmitting on the antenna of cell B…
Other than that, I leave it to nokia experts 🙂
pix2nd January 2009 at 08:20 #55216Hi All,Guest
I have also faced this problem in my network and i found that there were some implementaion issues like,
1) If u r not using a dual band antenna, then there may be possibility that the 2 GSM (900 & 1800) may be facing in a different dxn or may installed in a diffrent cell.
2)And, there may be a swap.
FYI, we are using LAR=-80, LER=-95 & NBL=5.26th February 2009 at 11:49 #55217RexGuest
we have a pb, High Incomming HO congestion in some cells. Cells have enough free resources. RTCH_assign_congestion_rate is low. Nb of Inc_HO_requests is not high. How could be congestion if there are free resources? Vendor-Alcatel. What could be wrong? Parameters, timers …
Please help!26th February 2009 at 12:52 #55218PixGuest
I can help !
Are those cells concentric cells ? Or Multiband cells ?26th February 2009 at 13:06 #55219RexGuest
They are not concentric nor multiband. Frequency hopping-SFH. We are using P-GSM and E-GSM. First and second TRX in P-GSM, the others E-GSM.
Regards,26th February 2009 at 18:02 #55220PixGuest
In which release are you ?
There might be a problem in the frequency band allocation.. MS are not G1 and the only TS left are in TRX using a G1 freq. ? That sounds weird… because you’d see normal assignment congestion as well.
If you know your indicators well enough you can give me the values for the indics below… But please reply with the full RNO indicator name 🙂
at busy hour only:
*in family RTCH Handover
TCH Handover congestion rate
Number of TCH Handover Requests
*in family RTCH Assignment
TCH Normal assignment congestion rate
Number of TCH Normal Assign Requests
* in family RTCH Traffic and Resources > Traffic
TCH erlang, TCH capacity (static)
* in family Traffic Model (or something like this)
Look for something that give the ratio of MS that can support the G1 band. I’m not sure it exists… 🙂
Now, per TRX, still at the same hour:
number of incoming HO requests, number of TCH normal assignment requests, TCH erlang
Then, per adjacency. Let’s say you’re looking at cell A which is HO incoming congested.
Select all adjacencies from cell A to its neighbors, and right-click / add reverse adjacencies.
Select all indicators located in the family “MATRIX” : Request, Allocated (or attempt?? I forgot) and Success
If you prefer, send me an excel report (or several) at this email pix_erlang at yahoo dot com.
Pix26th February 2009 at 19:31 #55221RexGuest
I appreciate your help. As soon as I prepare the excel file I’ll send to your e-mail.
Thanks again.3rd March 2009 at 12:55 #55222RexGuest
I’ve sent you an e-mail regarding HO_incoming_congestion.
BR3rd March 2009 at 18:16 #55223pixGuest
i didn’t receive anything.