high SDCCH congestion

[almoqbali36]

hi all

some cells in the network have sudden high SDCH congestion.
i check SD raffic at that day but no increase in traffic and there is no TX issue in the cell.
this happend to some cells like ones or twic a month but for differnt cell.

please any one can explain why?

E******* vendor

[plannerguy]

Hi

Nearby sites may had outages...


Regards
Plannerguy

[almoqbali36]

but there is no increas in SD traffic !

[kaizzer545]

What about transmission if its not stable users wont register normally in network using constantly SDCCH channel in otherwise what about SMS traffic give us more details about ir

BR

[rishi]

waht about directed retry u can try to implement it on that congested cell

[auto_art]

hi all

some cells in the network have sudden high SDCH congestion.
i check SD raffic at that day but no increase in traffic and there is no TX issue in the cell.
this happend to some cells like ones or twic a month but for differnt cell.

please any one can explain why?

E******* vendor


a lot is needed to analyse here. pl share site data & config.

have u turned ACSTATE on??

[jainapurvab]

Check below stats

1) TA report- this will indirectly suggest call requests from far ranges if surrounding cell coverage is affected.

2) BCCH and BSIC or BCC plan. co BCCH-BSIC plan in between any cells can cause Phentom request and thus SD congestion.

3)check any surrounding BSC shifting for LAC update.

Apurva Jain.
R.F. Engineer.

[_lisi4king]

Check below stats

1) TA report- this will indirectly suggest call requests from far ranges if surrounding cell coverage is affected.

2) BCCH and BSIC or BCC plan. co BCCH-BSIC plan in between any cells can cause Phentom request and thus SD congestion.

3)check any surrounding BSC shifting for LAC update.

Apurva Jain.
R.F. Engineer.

Can you describe in detailes Phentom request? How is it possible? What do you make on your network to avoid this problem?

[moayash]

What about transmission if its not stable users wont register normally in network using constantly SDCCH channel in otherwise what about SMS traffic give us more details about ir

BR

[jainapurvab]

Can you describe in detailes Phentom request? How is it possible? What do you make on your network to avoid this problem?


According to GSM spesification,

RACH is identified by BTS using 3 parameters.

-BCCH, BSIC(spesifically BCC) and delay which get refelcted in guard burst in RACH(thats why RACH guard bits are 68.25 approx and from this TA is calculated before synch.)

Think of two neighbor cells having same BCCH and BSIC.
GSM specification has same protocol for access burst sent for target cell during handover synch after receiving handover commanad from source cell AND channel request on RACH.

If network is synch. 4 burst are sent during handover which is also heard to BTS having same BCCH and BSIC.In reply BTS assumes new channel req. on RACH and forwards to BSC for allocation which in turns allocates false channels.

NOTE: SINCE NEW STANDARDS SUGGESTS THAT T3101 TIMER IS NOT SUITABLE FOR SDCCH DROP because this are triggered by above channel request procedures and some times ghost requests due to noise in receiver end. HENCE THIS COUNTER IS NOT SEEN IN SDCCH DROP,(btw check yr KPI whether its using couter or not-if yes then it will introduce SD drop also in phentom req.)

Hope this clearifies...

Apurva Jain.
RF,India.
GTL LTD.

[jainapurvab]

What about transmission if its not stable users wont register normally in network using constantly SDCCH channel in otherwise what about SMS traffic give us more details about ir

BR

Sorry but i do not see any reason of SD congestion due transmission error.

Consider case one by one

Abis fail after receiving RACH request.

since Abis is failed BSC can not get channel allocated confirmation from BTS and hence no channel allocated.

Abis fail after channel allocation= SD drop under counter Abis fail_Sd drop since no feeback sent by BTS during time of waiting for immediate assignment handshake sent by MS)

Abis fail after Handshake- SD drop under abis fail.

User will experience irritating rejection due toggling though.

registeration and ciphring is done after LAPDm signalling establishment and Abis fail will break signalling which eventually counted as SD_drop scenario.

SMS can affect congestion though

Apurva Jain.
R.F.,India.

[jainapurvab]

waht about directed retry u can try to implement it on that congested cell


Well!!

can you avoid SD congestion using DR?

I think you can not.
DR can be used to un burdened TCH and thus free TCH congestion not SD.

SD con. can be avoided by

1)LA shifting
2)Hystersis
3)inc. SD slots.
4)REDUCING COVERAGE OF CELL BY TILTS OR MIN ACCESS LEVEL.

Apurva Jain.
R.F.,India.

[komitko]

Are the cells located near a LA border or a country border?

[Aircom]

Dear All,
but he said thats the traffic is stable in site, which mean somthing wrong in abis interface,

[jainapurvab]

Well I suggest-

A) perform drive test in that time to see any service rejection request which will tell to increase sd

B) not sure but make sd handover ON and higher priority handover on load bases from this cell to target cell.

[gprastomo]

Can you tak the SDCCH usage distribution, SMS, MOC,MTC, Paging etc ?
Did the behaviour was chanign ?

Also please check the config, like SDCCH channel and Dynamic TCH SDCCH ?

Maybe the you have problem with Dynamic TCH SDCCH ? especially during the high TCH traffic so it cant be SDCCH Channel, so even SDCCH Traffic was stable, but if you have problem with Dynamic SDCCH so, you ll have congestion on SDCCH.
Try to remove Dynamic SDCCH, or Try to put the SDCCH on the good TRX.

[ritgail]

hi all

some cells in the network have sudden high SDCH congestion.
i check SD raffic at that day but no increase in traffic and there is no TX issue in the cell.
this happend to some cells like ones or twic a month but for differnt cell.

please any one can explain why?

E******* vendor


Have you got the resolution.

[blackhole]

Hi,
What kind of SDCCH traffic do you mean? Is it the number of request or traffic when SDCCH assign is success? As far as I think, SDCCH cong happen because of the increase of SD request, however, the number of success is maybe still the same.
SDCCH usually happen due to the increase of SDCCH request (normally because of Location Update).

[veasna]

Hi Bali36,
Is that problem happening on different cells in the same BSC ?

[justdream]

Maybe the you have problem with Dynamic TCH SDCCH ? especially during the high TCH traffic so it cant be SDCCH Channel

Dear gprastomo, Welcome :-)
what do you mean by above comment?
According to my understanding of Dynamic SD:

TCH/ SD dynamic converstion start when SD became too much busy based on Defined threshold (for example only 2 TS free)

TCH/ SD dynamic converstion stop when reach Defined threshold value (for example only convert 4 TS to be dynamic)

So what do you mean by "during the high TCH traffic so it cant be SDCCH Channel"?

[ohumayun]

Its better to check the SDCCH usage for the cell. SD traffic and SMS are just few of the things that can cause the increase. We can also look into the LU that those cells are doing. Location updates can increase if this cell is on the BSC boundry or if there is fluctuations on the cell. You can also look at the SDCCH drop for the cell as well as availability issues on it.

[timedomain]

if there is sudden increase (like 0 to 20-30%) and sd traffic is constant, it is because of transmissioni no need to check anything, just check the alarms