In the zigbee specification rev 22 on the page 394/599 I saw that the best path to a node in a mesh network is found during a route discovery process.
But I did not get what is triggering the route discovery itself.
Does somebody have a clue?

Above page 394/599 there is an explanation about the routing cost. after 394/599 it explain how nodes process a route request regarding his role.
What I’m expecting is that route discovery is firstly triggered if there is no route available in the routing table of a node and then if a specific period is elapsed the route discovery is launch again