Possible cause if both MO and MT CSFB calls are getting failed

Hi All.

Kindly suggest what could be the possible cause if both MO and MT CSFB calls are getting failed.

Can you please provide more details?

Is it single site or all network?
Did it work fine before and now zero or is it a new site?
Live network or test scenario single users?

It’s a region.
It was working fine before and it’s a live network.
Both MO and MT impacted for CSFB to 2G while calls are maturing fine in 2G only mode.

Then you need to compare 2 parts before and after the degradation.
Radio switches and freq configurations.
Core activities if any actions taken.

Redirection is happening towards 2G and then calls are not maturing.

What is the scenario?
Which phase exactly is failing in 2G side?

Was there any LAC change done recently?
If yes, please delete and recreate 4G to 2G relations.

Was there any change in BCCH list?
If yes, please add new set of freq in eNodeB.

Is it 100% FAILURE or some %?

No changes.


Check the configuration CSFB and MO parameters for the LTE side.
And priority.

Please check layer priority, freq band id, and BCCH frequency set.

Priority is on 2G and the same was earlier also.

All is correct.

Thanks All For ur responses …We got the solution .Actually We have MSC in pool and the association of the MSC which was mapped for CSFB with BSC were removed due to some consolidation activity so we have changed the mapping and issue got resolved.

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