In which condition eNB sends RRC reestablishment reject msg to UE?

Hello Experts.

In which condition eNB sends RRC reestablishment reject msg to UE?
RRC resources are available.
No issue of timer expiry.

If the context is deleted.

Or if the cell where the reestab is done has no neighbour relation with failure cell.

If eNB don’t have UE context AND:

  1. RRE do not contain last cell it was connected to OR
  2. eNB could not find nbr cell with PCI which UE was attached last time.

Both are neighbors in nbr list.

How to check in UE log if target cell has UE context or not?

You cannot check in UE logs. Only in S1 trace.

You cant check it from UE logs.
For Samsung eNB, you should have callp logs.

I understand only possibility in this case is UE context not present at target ENB, so what are possibilities of UE context missing at target eNB?

Target enb doesn’t have any s1/x2 related issues and alarms.

your question has already been answered mostly.
A working healthy X2 link is a must to fetch the context information where UE was camped previously.
If no X2, faulty X2 will all cause the said situation.

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HO failure, because Original eNB UE was communicating is the one RRE was triggered but it was sent to different eNB at same frequency while HO is done. Rej is sent to the UE because RRE was triggered at different cell.

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No, UE context means handover preparation was not done.