X2 handover is initiated if the If the target cell is served by
the same MME as the current cell and there is an X2 interface
with the target eNodeB is available.
The source eNodeB decides to initiate an S1-based
handover to the target eNodeB if it does not have an X2
interface with the target eNodeB. (The S1 handover can
also be triggered if the X2 handover had failed).
Just to add what Sudhansu has mentioned, NRT (Neighbor Relationship Table) play a major role while initiating handover. ANR (Automatic Neighbor Relationship) , one of the SON feature is used to update NRT table which tells whether X2 link is available and active with neighbor or not. If X2 link is active then X2 handover shall be executed else S1 handover procedure.
Can you explain me when we will prefer A2 and A3 events for measurement report?
And is there any relation between the events?
What are these Ms,Hys,Thresh,Ofn,Ocn,Mn and how ENb will set these values in the meas config?