Multi-class data transport

An apparatus for controlling the forwarding of a flow of data units across a network from a sender node to a receiver node via at least one intermediate node, said data units each having one of a plurality of different types of class indication associated therewith, each type of class indication providing, to an intermediate node currently processing the data unit with which said class indication is associated, an indication denoting a particular class of treatment, selected from a plurality of different classes of treatment, according to which said data unit is to be processed by said intermediate node, a proportion of the data units of said flow being forwarded as a first sub-flow comprising one or more data units each having a class indication of a first type thereby providing an indication denoting a first class of treatment;

• said apparatus comprising a computer configured to perform at least:
• monitoring a flow characteristic to obtain a measure of a predetermined dynamic flow characteristic indicative of progress of said flow;
• monitoring a flow progress to determine, in dependence on said measure of said flow characteristic and on a predetermined threshold level for said flow characteristic indicative of a threshold level for the progress of said flow, whether the progress of said flow as indicated by said measure is within a predetermined range bounded by said threshold level for the progress of said flow;
• and
• controlling a sub-flow for, in the event of a determination that the progress of said flow as indicated by said measure is not within said predetermined range, arranging for the proportion of data units of said flow subsequently forwarded from said sender node to said receiver node as said first sub-flow to be decreased, and for a proportion of data units of said flow subsequently forwarded from said sender node to said receiver node as a second sub-flow to be increased, said second sub-flow comprising one or more data units each having a class indication of a second type thereby providing an indication denoting a second class of treatment different to said first class of treatment.