If LTE to 3G neighbors not defined, will there be NO CSFB attempts?

Hi Experts.
If LTE to 3G entire NBR not defined, will there be NO CSFB attempts?

If legacy 3G site is defined, it should work, I think.

In Huawei yes: NO CSFB without nbr definition!

No CSFB prep also.
Prep attempt will be zero.
Success will be zero but prep attempt.
Because switch is defined, but nbr no.

In Huawei you need to set the priority in UTRANNFREQ or UTRANNCELL when the CSFB is BLIND to works fine.

In Huawei: For Measurement-based Handling is not necessary to set UtranNCell or UtranNFreq) priorities. For Blind handling you must to set priority at Neighboring UTRAN frequencies (UtranNFreq) or neighboring cell (UtranNCell) to CSFB work.

CSFB to GERAN using blind redirection (neighbor relationships with GERAN cells have NOT BEEN CONFIGURED)


CSFB to UTRAN using blind redirection (neighbor relationships with UTRAN cells have NOT BEEN CONFIGURED)

This is Samsung network, and they don’t have blind support in network. I don’t know why.
And NBR miss so if defined CSFB will work, I guess.

If eNB just define neighboring umts freq, no umts neighboring cells, still csfb preparation.

Yes agreed, but in my case no CSFB prep.
As blind is disabled in network.
UMTS freq defined.

So you can check activation parameter/switch.

This is TAC lac issue.
Both sites have same TAC and no other site is with this TAC.
Core definition issue I believe.

TAC LAC mapping wrong at MME is not related to no CSFB prepare at RAN.
Even TAC LAC mapping wrong at MME, MO UE is still successfull, just need location update at 3G.

But no CSFB prep.
Switch and ARFCN defined.
There is no nbr but switch and uarfcn defined.
Something unusual.
May be no mapping done.

Do you see initial_context_setup_req or modify_context message from MME?

Yes I see s1 response fail.
What is the reason?
In csfb ps out, context request happening but no response.
But less attempts.
They have CSFB ps out in irat.

Do you see many S1 context setup/modify from MME?

Update: It was TAC issue, solved now. Thanks you all! :wink:

Thanks for feedback.
TAC configured wrong or tac-lac mapping wrong?

TAC wrongly defined at eNodeB.
(TAC was wrong at eNodeB itself).

One thing very special.
Even if 4G RAN enodeb disable csfb function, some UE initiating csfb service, not received rrc conn release from enb, after 10s or 20s UE can fallback to 3G by it self.