A method of communicating predicted network behavior includes generating network topology structure data describing at least part of a topology of a first network. Demand structure data is generated, the demand structure data describing at least some traffic demands relating to a source in the first network and a destination in a second network, wherein there are a plurality of network links between the first network and the second network. Traffic routing change data, describing at least one change scenario which would require a change of traffic routing, is generated. This data is then used to calculate change data that describes a routing of traffic through each of the plurality of network links between the first network and the second network for the at least one change scenario. The change data is transmitted to the second network.