CSFB not working if technology off air

Experts:
In Huawei if you set the CSFB as BLIND REDIRECTION and if this specify technology that you set as “INTERRATHIGHESTPRI” in MO CSFALLBACKBLINDHOCFG, get off the air, the CSFB won´t work.

Do you know about that?

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Example:
BLIND REDIRECTION and Highest Priority InterRAT as UTRAN.
If 3G get off the air, the CSFB won´t work to 3G and 2G.

Yes, right.

If you change to MEASUREMENT will work to 3G or 2G.
Summary: In BLIND the CSFB works only to INTERRATHIGHESTPRI, but this technology needs to work. Don´t work to INTERRATSECONDPRI!

There is a timer also if one rat failed based on measurement then it will attempt blindly.
CSFB protection timer.
And a counter to monitor or CSFB timeout like that.

Sure, thanks!
Now, please try to explain me something?

I turned it off the 3G cells (DEA all 3G Cells in this site) to test and somethings the CSFB works to 2G (BLIND REDIRECTION and INTERRATHIGHESTPRI=UTRAN).
How the KPI to CSFB 3G still working in this site?

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Sometimes I saw with the DT Team that CSFB worked to 2G (3G was OUT).
How do I have CSFB to 3G and not for 2G?
(3G and 2G belongs to the same BSS).

You only defined co-located 3G NBR in NCell?

Yes, but there weren´t 3G coverage in this area.
It’s a isolated site (only one).

Have you changed highest priority to GERAN for this isolated site?

No, I didn´t change.
Of course if I change the CSFB will work to 2G.

The question is: How do I have CSFB to 3G in Huawei KPI if the cells weren´t OUT?

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Because it’s blind, 4G will release to 3G due to highest priority blindly, weather there will be any 3G coverage or not.
If eNB redirect it to 3G then this counter will pegged.

OK, thanks.
So, in BLIND the KPI always peg in highest priority. Right?
Another explanation for not having the CSFB KPI for 2G is that when the call went to 2G, the mobile must have registered on the network, after having lost signal and received a page. This would be the reason for not having CSFB for 2G, because it wasn’t actually CSFB.

Yes, because frequency and NBR selection is second step while RAT selection is first step.

eNB will select highest priority RAT for blind redirection, since its blind it will redirect it wether 3G is there or not.
Counter 2G not pegging isssue.
Better to do measurement based and give CSFB protection timer of 2-4s.
If measurement based failed on 3G then it will blindly redirect to next technology.