Abstract: A communication scheme for a multi station message transmission system involves the transmission of messages from one station to another, a return message from the receiving station and the retransmission of a previously transmitted message if an acknowledgement is not received. Each message, which may or may not contain data, includes a header having a sequence bit and an acknowledge bit. Each station within the communication system stores in memory a transmit sequence bit and a receive sequence bit. The header of each message that is transmitted from a given station contains a sequence bit corresponding to the state of the transmit sequence bit stored at that station. When a message having an acknowledge bit is received, the state of the stored transmit sequence bit is switched.

Abstract: A multiple services system using telephone lines to supply various data services to subscribers, including alarm surveillance, meter reading, energy management and digital data service, provides a multi-conductor subscriber bus at the subscriber premises for selective connection of plural data service terminals to the system and a switching communication controller at the central office which acts as a concentrator for the transmission of alarm, meter reading and control signals between the subscriber data system and a central control system, while acting as a switch for the connection of the subscriber data system to a data service system for transmission to the subscriber of digital video display data on request. The transmission over the telephone lines is transparent to normal telephone service and all communications within the system, including those on the subscriber bus, are effected in accordance with a predetermined link control protocol.

Abstract: A variable permeability magnetic object detection device including an electromagnetic sensing coil; a core disposed in the electromagnetic sensing coil having a first permeability when the core is magnetically saturated and a second different permeability when the core is magnetically unsaturated; a magnetic member proximate the electromagnetic sensing coil for providing a magnetic field in the core for operating the core in a magnetically saturated state without a magnetic object to be detected present in the area proximate the electromagnetic sensing coil, interacting with the magnetic field, and for operating the core in a magnetically unsaturated state with the magnetic object to be detected present in the area proximate the magnetic sensing coil, interacting with the field; and a detector responsive to said electromagnetic sensing coil to detect the presence of a magnetic object.

Abstract: A variable permeability magnetic object detection device including an electromagnetic sensing coil; a core disposed in the electromagnetic sensing coil having a first permeability when the core is magnetically saturated and a second different permeability when the core is magnetically unsaturated; a magnetic member proximate the electromagnetic sensing coil for providing a magnetic field in the core for operating the core in a magnetically saturated state without a magnetic object to be detected present in the area proximate the electromagnetic sensing coil, interacting with the magnetic field, and for operating the core in a magnetically unsaturated state with the magnetic object to be detected present in the area proximate the magnetic sensing coil, interacting with the field; and a detector responsive to said electromagnetic sensing coil to detect the presence of a magnetic object.