METHODS AND APPARATUS FOR TRANSMITTING DATA

Methods and apparatus are disclosed for transmitting flows of data units across a data communication network from a transmitting node towards an intended destination via one or more intermediate nodes, the data units having destination indications, the intermediate nodes being configured to receive data units, identify therefrom a transmission mode that has been selected from at least two transmission modes for the data units, and forward the data units according to the selected transmission mode. The method involves selecting a transmission mode for the flow in dependence on an estimate of the difference in the amount of a resource required to transmit the flow by one or the other transmission mode, a resource-usage measure indicative of the amount of the resource required to identify a route and reserve sufficient capacity thereon for transmission of the flow, and a probability measure indicative of a likelihood of success of an attempt to identify and reserve sufficient capacity for the flow.