What can be the reason of high number of x2ap_trelcoprepexpiry?

Dear Experts.

High number of handovers are getting failed on LTE site and reason is high number of preparation failure due to x2ap_trelocprepexpiry.

What can be the reason of high number of x2ap_trelcoprepexpiry?

System is Samsung.

Admin note: this post was updated with image below.


Specifies the maximum time for the Handover Preparation procedure in the source eNB.
Handover Preparation procedure is cancelled when timer TRELOCprep expires.

Main issues is check the target sites board related alarms / target sites unavailability situation by hourly / target sites utilization or congestion / Target sites-cells incoming handover quantity and compare with nearby sites-cells

x2ap_trelcoprepexpiry message is related to the X2 Application Protocol X2APP. Upon reception of the HANDOVER REQUEST CKNOWLEDGE message the source eNB shall stop the timer TRELOCprep, start the timer TX2RELOCOverall and terminate the Handover Preparation procedure.

The source eNB is then defined to have a Prepared Handover for that X2 UE-associated signalling.

If there is no response from the target eNB to the HANDOVER REQUEST message before timer TRELOCprep expires in the source eNB, the source eNB should cancel the Handover Preparation procedure towards the target eNB by initiating the Handover Cancel procedure with the appropriate value for the Cause IE, e.g. “TRELOCprep expiry” .

Check admission control failures in target eNodeB.

Will bh related issue lead to this problem?

Target site is having Backhaul related issue.

It’s mw site and it’s ring is open.

It means call flow fails at area highlighted in yellow:

More precisely it fails here:


Now concept is pretty much clear!