Interfacing between radio units in a base station in a mobile communication system uses a common public radio interface CPRI for streaming IQ data samples arranged in lanes. A separate serial interface sRIO is now additionally used for transferring selected data samples arranged in packets, the selected samples corresponding to selected lanes streamed between other radio units via the common public radio interface. In the radio unit, the selected data samples are arranged in packets to be transmitted via the serial interface, and, vice versa, the selected data samples arranged in packets received via the serial interface are arranged in lanes. A system timer coupled to the CPRI generates a timebase for controlling the sRIO interface in order to have it synchronized. Advantageously the data sample transfer capacity of the streaming CPRI interface is extended using the packet based serial interface.