Solution for reducing timing uncertainty is provided. The solution means for receiving data in a first clock domain; means for selecting in the first clock domain a data unit to be a frame starting point and transmitting the information on the selection to a frame counter in a second clock domain; means for performing to the data in a coding/decoding unit coding or decoding, the coding/decoding unit several clock domains; means for obtaining at the output of the coding/decoding unit the position of the selected frame starting point; and means for determining timing of the correct frame starting point of the coded/decoded data utilizing the obtained position of the selected frame starting point and the information in the frame counter.