Why do we have RRC reestablishment rejects on LTE?

Hello Experts.

Question about RRC reestablishment rejects on LTE: why do we have rejects?

There are 2 causes for this:

  1. First is when old PSC where RLF happened is not neighboured with PCI where reestab happens so eNodeB canntop retrieve UE context from old eNodeB.

  2. Second cause is when security mode is not yet active.

Is there another 3rd reason?

May be → source eNB did not replied to RLF indication message form target eNB?

Yes, this could be another reason.

In Samsung we have seen many reestab rejections when there is UMP overload at eNB.

Ump overload is due to high rrc resources or high signalling flow and when it reaches to 95% of capacity, it rejects all RRC establishment and reestablishment.