In order to prevent in a communication system covering at least one cell for wireless communication, the system having a line-limited or across-line wireless direct communication possibility between mobile phones that is synchronized with a base station, that mobile parts attempt to synchronize in the communication system with a continuous broadcast downlink service provided by a hybrid mobile part, it is proposed to mark the continuous broadcast downlink service of the hybrid mobile part, which assumes the role of a radio fixed part, so that mobile parts, which want to synchronize with a true radio fixed part, can detect that the service provided by the hybrid mobile part is not permanently available, or even incomplete.