A method of transmitting a tributary in synchronous mode at the level of a link of a data network is disclosed. The tributary comprising at least one frame including at least one payload envelope area and one transport overhead area. The envelope area includes at least one payload and load supervision data related thereto. The transport overhead area includes transport supervision data related and an area of fixed patterns. The method comprises modifying a frame to create a modified frame and transmitting the modified frame. Modifying the frame comprises: part of the fixed patterns are deleted from the fixed pattern area; the positions of the part of the fixed patterns deleted are recorded; replacement data are inserted at the level of the positions. The method is characterized in that the replacement data comprise the transport supervision data of the frame of the tributary.