What can be the reason of 100% IRAT (4G to 5G) Handover getting failed in Preparation phase?

RAN
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21

You will need network traces.

Follow this call flow:

22

Core support HO from 4G to 5G?

Are you sure bts it is enabled?

23

Yes.

Thanks, I will.

24

This is the correct signalling for 4G to 5G handover (SA):

eNB sends HO required to MME?

25

Happening in other circles of same operator? I think this is specific to one particular eNodeB.

26

I would love to see 4G 5G relation info, seems like a prep fail.

Dont trust ANR if ANR parameters are not optimized, UE would not have time to measure 5G CGI.

27

I will get eNB traces later.

In UE logs it’s visible that UE is continuously sending B2 measurement report.

But HO command is not seen.

UE receives RRC release message from eNB and latches to 5G via redirection.

28

Update here:

Issue Identified -eNB S1 AP version in MME was older one - while other eNB’s are having latest S1 AP Version in MME.

Thanks all for support!