CSFB LTE to GERAN Call setup time (CST) optimization

[linhhy]

Dear friends,

I'm optimizing CSFB CST from LTE to GERAN. I deployed CSFB with RIM feature to reduce the time for UE reading 2G SIB after redirection from LTE. But I saw 2 different cases with Sony XZ Premium and Samsung Note 5. Sony XZ Premium has less time to start "CM service request" when compared to Samsung Note 5, it means less CSFB CST. Samsung Note 5 needs to wait for SIB 2 type before starting "CM service request" while Sony XZ did not.

Based on the standard (3GPP 44.108 3.2.1) MS no need to re-read any message if it has in the E-UTRA RRCConnectionRelease message. It's different with the real test case.

Could anyone can help me the reason why does the MS read some SIB in 2G before making "CM Service Request" and Why does it have the different procedure on 2 phones.

Many thanks,


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[plannerguy]

Hi

Some queries

Is this tested under same cell.?
Is data session on going ?

Rgds
Plannerguy

[linhhy]

Hi

Some queries

Is this tested under same cell.?
Is data session on going ?

Rgds
Plannerguy

Hi, it comes from the same cell and no data session on going.

[linhhy]

I tested a hundred calls and I saw the same procedure on each phone, but the difference between two phones.

It is clear that Sony device has much less time to start the call when compared to Samsung device which takes more time to wait for SIB 2 before making call setup. Can I cutoff SIB2 for all devices in this step?

When comparing 2 phones, it’s also made me confusing that Sony device can read SIB 1, 3, 13 in too short time. (it’s less than 2 multi frames while the standard requires around 4 Multi frames).

Here is a different time for starting call setup in 2G from LTE side between 2 phones at 100 calls:

41335

[karimos]

Hi linhhy,

Seems the problm is in 2G part. Noticed that there is an additional authentication phase for the 2nd mobile, which may be due to a mobile class mark issue at BSC level.

Did you check if there is class mark enquiry sent by BSC ? This leads to a further delay in call setup after CSFB has been triggered.

if it's the case, then it's not required as UE will report by itself the class mark change ( for Huawei vendor).

in this case the related parameter should be modified.

BR.

[linhhy]

Hi linhhy,

Seems the problm is in 2G part. Noticed that there is an additional authentication phase for the 2nd mobile, which may be due to a mobile class mark issue at BSC level.

Did you check if there is class mark enquiry sent by BSC ? This leads to a further delay in call setup after CSFB has been triggered.

if it's the case, then it's not required as UE will report by itself the class mark change ( for Huawei vendor).

in this case the related parameter should be modified.

BR.

Hi Karimos,

The problem here is the process of searching 2G network between different phones.