A method performing a measurement on a data flow at a node of a communication network, the data flow including data units transmitted during first and second block periods marked by respective first and second marking values, the first and second block periods alternating in time. The method includes, at the node, during a current block period: a) determining a first parameter relating to the data units received at the node during a preceding block period; b) receiving from a further node of the transmission path a first data structure including a second parameter relating to data units transmitted to the node during the preceding block period; c) processing the first parameter and the second parameter for providing a result of the measurement on the data flow; and d) transmitting to a still further node of the transmission path a second data structure including the first parameter.