A multicommodity flow in a network routes several specified source-destination demands simultaneously, subject to a common capacity constraint on each graph edge. In a fractional multicommodity flow, a demand may be split among several paths. For an undirected graph edge, traffic in both directions shares the same capacity (Langberg and Médard 2009).
The Langberg-Médard conjecture gives a sufficient condition for such routing after the orientations of a directed multicast network are removed.
