pmNoCellFachDisconnectAbnorm -High PS Drop KPI due to FACH disconnect abnormal-

[uchok]

I have problem with PS Drop KPI.
The cause is many Cell Fach disconnect abnormal.
I see high value in that counter.

I hope someone can help to explain to me the reason of high Fach disconnect abnormal.
I see that high ULRSSI doesn't always create high Fach disconnect abnormal.
Is it related to RF or is it always because of high traffic and cause some congestion?
Perhaps someone can guide me the counter to check related to it.
And I don't think this related to Fast Dormancy that is going on with Iphone.

[babak1349]

Hello, One of the reason of high FACH drop Could be high traffic So you need to check traffic created in Erlang for different services. Or you can check number of FACH users. If the FACH traffic is above 40~45 Erlang most probably you are facing FACH overload. In this cases the drop call initiated by UEwhich sends Cell update With the cause of "RLC unrecoverableError" I think it would be normal when we have a lot of users in FACH state and they may face delay in receiving data and UE interpret it as RLC data unrecoverable and informs it through cell update About Solution, I am not sure about parameters but you may delay moving users to go from HSDPA to FACH or accelerate moving users from FACH to URA But the fact is your cell is in high load in any case and you need to reduce the traffic by introducing new carrier or new sites Best regards
I have problem with PS Drop KPI. The cause is many Cell Fach disconnect abnormal. I see high value in that counter. I hope someone can help to explain to me the reason of high Fach disconnect abnormal. I see that high ULRSSI doesn't always create high Fach disconnect abnormal. Is it related to RF or is it always because of high traffic and cause some congestion? Perhaps someone can guide me the counter to check related to it. And I don't think this related to Fast Dormancy that is going on with Iphone.

[uchok]

Hi Babak thank you for the explanation.
Is there specific counter that can show it's having overload (congestion), for example like in RRC and RAB we can see counter RRC denied due to DL Channel (pmNoRrcReqDeniedAdmDlChnlCode) code or RAB Failure due to lack of DL Power (pmNoFailedRabEstAttemptLackDlPwr).



Hello, One of the reason of high FACH drop Could be high traffic So you need to check traffic created in Erlang for different services. Or you can check number of FACH users. If the FACH traffic is above 40~45 Erlang most probably you are facing FACH overload. In this cases the drop call initiated by UEwhich sends Cell update With the cause of "RLC unrecoverableError" I think it would be normal when we have a lot of users in FACH state and they may face delay in receiving data and UE interpret it as RLC data unrecoverable and informs it through cell update About Solution, I am not sure about parameters but you may delay moving users to go from HSDPA to FACH or accelerate moving users from FACH to URA But the fact is your cell is in high load in any case and you need to reduce the traffic by introducing new carrier or new sites Best regards

[babak1349]

Hi,
I don't think you can find a counter which shows you overload situation in FACH/ RACH state. I appears just like as drop call which has been initiated by UE. You can look at the number of FACH users, or FACH traffic in Erlang or FACH traffic volume in order to see the utilization of FACH channel.

BR

[electron]

I faced some times FACH drop increasing with out any reason and after cold restart problem could be solved( Of course if the case is for specific RBS or cell)
Hi,
I don't think you can find a counter which shows you overload situation in FACH/ RACH state. I appears just like as drop call which has been initiated by UE. You can look at the number of FACH users, or FACH traffic in Erlang or FACH traffic volume in order to see the utilization of FACH channel.

BR

[shamim23]

Hi All

One can calculate FACH load from RBS counters as below:

Total FACH load:

i. (pmNoOfTfc1OnFach1+pmNoOfTfc2OnFach1+pmNoOfTfc3OnFach2)/(measurement period (sec)*100)

b. FACH1 load:

i. (pmNoOfTfc1OnFach1+pmNoOfTfc2OnFach1)/ (measurement period (sec)*100)

c. FACH is considered loaded if:

i. Total FACH load is > 80% and FACH1 Load is > 30%.

From RNC:

FachPayload = pmDlTrafficVolumePsCommon

If above is crossing 16 kbps per ROP then cell is considered to be FACH overloaded

Hope this helps.

KR
Shamim

[electron]

Could you please share/address to the reference ?

Thanks
Hi All

One can calculate FACH load from RBS counters as below:

Total FACH load:

i. (pmNoOfTfc1OnFach1+pmNoOfTfc2OnFach1+pmNoOfTfc3OnFach2)/(measurement period (sec)*100)

b. FACH1 load:

i. (pmNoOfTfc1OnFach1+pmNoOfTfc2OnFach1)/ (measurement period (sec)*100)

c. FACH is considered loaded if:

i. Total FACH load is > 80% and FACH1 Load is > 30%.

From RNC:

FachPayload = pmDlTrafficVolumePsCommon

If above is crossing 16 kbps per ROP then cell is considered to be FACH overloaded

Hope this helps.

KR
Shamim

[uchok]

Hi shamim23, from the formula you gave me, I can see that the site is Cell FACH overloaded like the one I have now.

#High FACH disconnect abnormally
Object Counter 19:00
UtranCell=XXXX pmNoCellFachDisconnectAbnorm 646


#Check if it's overload
##Get the FACH counter
Object Counter 19:00
Sector=2,Carrier=2,Sccpch=3016 pmNoOfTfc1OnFach1 16211
Sector=2,Carrier=2,Sccpch=3016 pmNoOfTfc2OnFach1 16020
Sector=2,Carrier=2,Sccpch=3016 pmNoOfTfc3OnFach2 45685


##Total FACH load:
[(16211 + 16020 + 45685) / (900*100)] x 100 % = 86,57 %


##FACH1 load
[(16211 + 16020) / (900*100)] x 100 % = 35,81 %




So Total FACH load > 80% and FACH1 load > 30%.
The site is having Cell FACH overloaded.

The formula is very useful.
But can you share the reference ?
I would really be grateful.





Hi All

One can calculate FACH load from RBS counters as below:

Total FACH load:

i. (pmNoOfTfc1OnFach1+pmNoOfTfc2OnFach1+pmNoOfTfc3OnFach2)/(measurement period (sec)*100)

b. FACH1 load:

i. (pmNoOfTfc1OnFach1+pmNoOfTfc2OnFach1)/ (measurement period (sec)*100)

c. FACH is considered loaded if:

i. Total FACH load is > 80% and FACH1 Load is > 30%.

From RNC:

FachPayload = pmDlTrafficVolumePsCommon

If above is crossing 16 kbps per ROP then cell is considered to be FACH overloaded

Hope this helps.

KR
Shamim

[shamim23]

Hi

You won't find this in Alex. But this is what is used in E/// to calculate FACH load.

KR
Shamim

[dadoba]

Guys then I understand that the only way to solve a problem like this is reducing the traffic of this cell, adding new carrier or new site right?

Do you have other suggestion like parameters to check and some optimization that can be done?

Thank you

[babak1349]

Hi,
First you need to balance the traffic on HSDPA and FACH But you should consider smart phones can generate small spike of data transfer and need to be on FACH So you need to optimize throughput over HSDPA
One way is to increase the number of S-CCPCH and reduce FACH utilization
Please note if it happens in optimized network , it happens due to high number data users on both HSDPA and fACH so obviously you need to add more carrier or new sites

Cheers

[dadoba]

Hello how can I do that? Increase the number of S-CCPCH. I checked here and I have 2 S-CCPCH per cell but when I get the pmx only one is incremented the other is 0 in all the cases.



MO Attribute Value


Sector=1,Carrier=2,Sccpch=1020 SccpchId 1020
Sector=1,Carrier=2,Sccpch=1016 SccpchId 1016
Sector=1,Carrier=1,Sccpch=20 SccpchId 20
Sector=1,Carrier=1,Sccpch=16 SccpchId 16
Sector=3,Carrier=2,Sccpch=5016 SccpchId 5016
Sector=3,Carrier=2,Sccpch=5020 SccpchId 5020
Sector=3,Carrier=1,Sccpch=4016 SccpchId 4016
Sector=3,Carrier=1,Sccpch=4020 SccpchId 4020
Sector=2,Carrier=1,Sccpch=2016 SccpchId 2016
Sector=2,Carrier=1,Sccpch=2020 SccpchId 2020
Sector=2,Carrier=2,Sccpch=3016 SccpchId 3016
Sector=2,Carrier=2,Sccpch=3020 SccpchId 3020

[babak1349]

Hello,
Unfortunately I don't have any guideline which explain how FACH can be added I checked alex lib and saw the sccpch is automatically created by system Based on what you sent, one Sccpch supports FACH and the other one supports PCH. to increase the FACH capacity might be possible to add new FACH channel but I am not sure at all
It is better to ask vendor what solution they have

Best Regards


Hello how can I do that? Increase the number of S-CCPCH. I checked here and I have 2 S-CCPCH per cell but when I get the pmx only one is incremented the other is 0 in all the cases.



MO Attribute Value


Sector=1,Carrier=2,Sccpch=1020 SccpchId 1020
Sector=1,Carrier=2,Sccpch=1016 SccpchId 1016
Sector=1,Carrier=1,Sccpch=20 SccpchId 20
Sector=1,Carrier=1,Sccpch=16 SccpchId 16
Sector=3,Carrier=2,Sccpch=5016 SccpchId 5016
Sector=3,Carrier=2,Sccpch=5020 SccpchId 5020
Sector=3,Carrier=1,Sccpch=4016 SccpchId 4016
Sector=3,Carrier=1,Sccpch=4020 SccpchId 4020
Sector=2,Carrier=1,Sccpch=2016 SccpchId 2016
Sector=2,Carrier=1,Sccpch=2020 SccpchId 2020
Sector=2,Carrier=2,Sccpch=3016 SccpchId 3016
Sector=2,Carrier=2,Sccpch=3020 SccpchId 3020