A method is proposed for determining the round-trip delay for sending multimedia data, such as voice or video data, between a first network node and a second network node over a communications network, where data is encapsulated in data units comprising at least one frame of encoded data. The method includes the steps of: said first network node sending a request for reconfiguration of the data unit structure to the second node; the first node detecting a reconfiguration response from the second node, where the reconfiguration response comprises at least one data unit of data having a structure that corresponds to the request for reconfiguration. The first node then measures the time elapsed between sending the reconfiguration request and detecting the reconfiguration response and determines a value for roundtrip delay using said measured time. In accordance with a first embodiment, the request for reconfiguration is a request to change the encoding mode of the multimedia data. A node adapted to measure this round-trip delay is also proposed.