The invention relates to data transmission in a telecommunication system. An information unit is asynchronously transmitted over a transmission link, such as a radio interface, in timing units called radio frames. Information units reside in successive radio frames, each radio frame includes at least one whole information unit and part of an information unit split in successive radio frames. Thus, the frames contain asynchronous information units. One or more bits in a radio frame is reserved for phase indication, based on which a receiver synchronizes to the asynchronous information units. Phase indication defines a sequence of N successive radio frames and indicates for each frame which of the N possible frames in the sequences said frame is. The receiving unit indicates phasing between the frames and the asynchronous information units in the frames by synchronizing to said phase indication.