It is disclosed a method for transmitting a bidirectional packet flow between two nodes of a packet-switched communication network. Each node applies a respective marking value to the packets to be transmitted to the other node. Each node switches the respective marking value applicable to the packets to be transmitted to the other node upon detection that the marking value applied to the packets which are being received from the other node has been switched. Before switching its respective marking value applicable to the packets to be transmitted to the other node, one of the nodes waits a wait time TW. A measurement point placed between the two nodes may provide RTT measurements based on the detection times of the switching of the applicable marking value in the transmitted packets. However, the measurement point may provide correct RTT measurements only if it knows the value of the wait time TW.