Improve representation of 'Request and Reply' / 'Round trips' in graphs
When a request and reply or round trip event links two modules, in the graphs the arrow only shows one direction. So just looking at the graph, one may think that the communication is one-way.
Maybe adding a arrow tail in case of request and reply would help to better understand that the communication is bi-directional. For round trip events, they may be considered as a combination of request and reply + broadcast. So the arrow tail trick would also work for the request and reply part of it ; adding the broadcast arrow would finalize the graph part of it.