It is disclosed a method for enabling a performance measurement in a packet-switched communication network. A first node and a second node exchange packets comprising a marking value, which they alternately switch between two alternative marking values. The second node in particular switches the marking value applicable to the packets addressed to the other node depending on the marking value comprised in packets received therefrom. The first node writes a sampling value in one packet addressed to the second node for each marking period. Upon reception of each packet comprising the sampling value, the second node copies the sampling value in a packet addressed to the first node. One or more measurement points may be provided between the two nodes, which provide performance parameters for the packets comprising the sampling value in both directions. Such performance parameters may be used for providing round trip time measurements.