- This topic has 98 replies, 1 voice, and was last updated 7 years, 10 months ago by chis.
18th June 2003 at 15:24 #35710gkGuest
Could you tell me what are all the actions to be taken to reduce SDCCH drops?11th March 2006 at 16:59 #35711Bouh52Guest
Check SDCCH MHT if this one exceeds 3,5 sec , check TCH blocking. Check related counters of SDCCH drop example due to ABIS, RF , A-interface etc.
Most common case is interference.11th May 2006 at 16:10 #35712silviaGuest
I just found about this forum and I think this is really useful! I am an RF engineer working for an operator using Nokia BSS and we have a site that is having many SDCCH drops (around 60%) on a LAC change border with 2 TRX. It used to work fine until 1 month ago.
We have alarm 7745 CHANNEL FAILURE RATE ABOVE DEFINED THRESHOLD but we have checked both TRX with a loop test and they seem to work properly, we changed SDCCHs from one TRX to another without any improvement.
We have checked interferences, cables, masses and Baseband cards but it has not improved.
Do you have any ideas what the problem could be and how to solve it?
thanks very much in advance!11th May 2006 at 20:41 #35713PixGuest
It suddenly happened that the SDCCH drop rate increased ? Did you change frequencies or the antenna design ?
When something like this happens (and I didn’t change anything on the site), I usually suspect a hardware problem.
Try resetting the Abis link, the TRXs, etc…
Then you can try to change the frequencies of the cell, and eventually go drive-test around this area.
As said ealier, check the Mean Holding Time (MHT). What is it’s vallue ? What about the TCH assignment success rate ? The Call drop rate ? The TCH MHT ?
Good luck Silvia, let us know how it goes…12th May 2006 at 10:59 #35714silviaGuest
the SDCCH drop rate increased all of a sudden and we did not change the antennas nor the frequencies, that is why we also suspect it is a HW problem but still could not find it.
The SDCCH MHT is around 9.5 but the site is on a LAC border change and we think this is due to the Location updates, not related to this SDCCH drop rate.
Thanks for the advice12th May 2006 at 20:10 #35715PixGuest
Even on a LAC border, the “SDCCH mht” will never reach 9.5 seconds. It’s way too much !
Does this cell handle a lot of traffic (TCH) or not ? If yes, then I advise you change the TRX’s or the cell combiner.
If you feel it is not a HW problem, then you can try increasing the Cell Reselection Hysteresis between both LACs, and increase the anti pingpong reselect timer. But in my opinion, you cell has a HW problem. Have you performed a drivetest on it ? what about other QoS indicators ?14th May 2006 at 09:34 #35716RF LearnerGuest
ur site is on LA border,
wat kind of signalling u r using.
let me know i will try to help.
my email ID is firstname.lastname@example.org May 2006 at 10:27 #35717OptimizerGuest
Wht are hte reasons of SD drop, i-e suddenly lost or Low SS UL/DL or bad qulity DL. Can u see these in ur system.3rd August 2006 at 09:32 #35718ManojGuest
The reason for SD drop is cochannel interference usually.Check your frequency plan24th August 2006 at 20:20 #35719BurkeGuest
Hi I am working with a company that utilizes Nortel Products and we have a couple of Dual Band sites i.e. 1900 and 850 MHz. I noticed that at a certain time in the night there is a sharp increase in SDCCH Failed Assignment Rates one of the 1900 sectors on a particular site.
Please Advise.30th March 2007 at 13:27 #35720bhaskarGuest
what is differnce between sd drop and sdcch blocking.plz explaine .30th March 2007 at 18:36 #35721PixGuest
SD DROP = SDCCH DROP = drop during a sdcch phase (for call assignment for instance)
SDCCH BLOCKING = SDCCH assignment rejected because all the SDCCH timeslots are busy (= congestion)8th April 2007 at 16:36 #35722bpGuest
which parameter depend on sdcch drop.20th April 2007 at 11:00 #35723fresh engineerGuest
what is the relation between lac and sdcch…plz explain it to me…am a fresh engineer22nd April 2007 at 08:51 #35724pixGuest
when a subscriber changes LAC, its mobile will trigger a location update procedure. This procedure takes place on the SDCCH channel.
– too many LACs will increase the amount of load on the SDCCH channels of the cells at LAC borders. This can lead to SDCCH congestion on the border cells, but also overload the BSC.
– locating a LAC border in an area where a lot of people are moving in and out, it will generate additional Location Update procedures.
– not enough LACs, meaning the size of a LAC is large, this might create paging problem : the subscribers locations is known at the LAC resolution, so when receiving a call, the MSC as to page for the whole LAC. Too many subs in a LAC : too many Pagings.