X2 HO preparation success rate suddenly decreased with root cause as invalid MME Group ID and MME Group ID is unique?

Question

X2 HO preparation success rate suddenly decreased in some sites. the root cause is invalid MME Group ID, however MME Group ID is unique. Could you please comment about issue ?

Answer 1

X2 handover is applicable where in source and target eNodeB both are connected to same MME and both eNodeBs having X2 link up.
Source eNodeB includes GUMMEI (MME identifier) in the handover request message. Target eNodeB first verifies whether it has connection with intended MME or not.
Just check the logs of S1 interface for both the eNodeBs to make sure both are connected to same GUMMEI. You can verify S1-Setup Reponse message. If everything is fine at S1 interface then verify GUMMEI value in X2 HO Request message.
There might be another case when both eNodeBs are connected with few common GUMMEIs not the same set of GUMMEIs.
Cause "Invalid MME group Id" shows that the target eNodeB does not have connection with MME group Id that was received in HO request.