It is provided a method, comprising checking if a value of a main correlation identifier comprised in a first correlation message received from a first node and a value of the main correlation identifier comprised in a second correlation message received from a second node different from the first node are the same, wherein the first correlation message additionally comprises a first secondary correlation identifier, and the second correlation message additionally comprises a second secondary correlation identifier; and the method further comprises generating, if the value of the main correlation identifier comprised in the first correlation message and the value of the main correlation identifier comprised in the second correlation message are the same, a main correlation message comprising the first secondary correlation identifier.