Abstract: A {\em good edge-labelling} of a graph $G$ is a labelling of its edges such that, for any ordered pair of vertices $(x,y)$, there do not exist two paths from $x$ to $y$ with increasing labels. This notion was introduced in~\cite{BCP} to solve wavelength assignment problems for specific categories of graphs. In this paper, we aim at characterizing the class of graphs that admit a good edge-labelling. First, we exhibit infinite families of graphs for which no such edge-labelling can be found. We then show that deciding if a graph admits a good edge-labelling is NP-complete. Finally, we give large classes of graphs admitting a good edge-labelling: forests, $C_3$-free outerplanar graphs, planar graphs of girth at least 6, subcubic $\{C_3,K_{2,3}\}$-free graphs.