According to the present invention a method and a device is provided for combining at least two data signals having a first data rate into a single data stream having a second data rate being higher than the first data rate for transmission on a shared medium or vice versa, said device comprises at least one port for receiving said at least two data signals and a port addressing unit for extracting data from the data signals received by said ports, wherein said port addressing unit is configured to place the extracted data at predetermined positions in said single data stream to be transmitted on said shared medium and at least one control data insertion unit is provided for placing control data in said single data stream. Thus, a method and device proposed implementing a multiplexing structure in which the data from M parallel low-speed channels are multiplexed onto a data bus operating with M times the data rate of the M low-speed channels. A multiple-stage process where, e.g., 28 T-1 (DS-1) channels are re-mapped into one T-3 (DS-3) channel and 3 T-3 (DS-3) channels are then mapped into an STM-1 frame is advantageously avoided.