Geographically distributed conference sites each have a telephone receiver and a dataconferencing appliance connected to a shared voice call network. The selecting circuit includes a first transistor in which the digital signal is supplied. The aim of the invention is to further develop such a riveting device in an advantageous manner. A current situation of the service subscriber is determined using subscriber context information based on private information of the subscriber. Access to the bus can be granted by the centralized bus arbiter to a winning bus master under any bus arbitration policies. The apparatus further includes a sync detection result output unit outputting a sector sync detection period when continuity exists in the detection of frame sync bits and in the detection of the 3-bit sector sync or 6-bit sector sync and counting a sync detection signal and a new sync detection period when a sector sync signal is detected by the sync detection unit.