A communication subscriber which, as a passive subscriber of a communication system, does not have its own transmission authorization but listens to all the communication processes and can receive only those data items which are also intended for it, which can be identified without doubt from destination...http://www.google.de/patents/US6687551?utm_source=gb-gplus-sharePatent US6687551 - Audio-active communication stations, communication method and communication system with audio-active communication stations
