An apparatus is provided for configuring data cells received in a telecommunications process in a continuous stream of data cells of fixed length and each comprising a header and a user data part. The apparatus comprises a processing unit, adapted and configured so that it is able to check data cells for the presence of empty cells, discard the data cells consisting of empty cells and then check the user data parts of the data cells less the empty cells—without the need to buffer the same—as to whether they belong together, and then to assemble the user data parts of the data cells belonging together into a frame. The apparatus may be integrated in, a modem and is also particularly suitable for data cells existing as ATM cells for receiving by an ATM system. The invention relates in addition to a correspondingly sequencing method for configuring data cells.