Nippon Telegraph and Telephone Public Corporation

Iwasaki Tsushinki Kabushiki Kaisha

Telegraph & Telephone Pub. Corp.

Kazuyuki Yamamoto

Koichi Sekiguchi

Hikaru Takematsu

Teruyuki Kubo

Seiei Ohkoshi

A control signal transmission system for a key telephone system, in which control signal information is transmitted in a parallel signal configuration between a plurality of key telephone sets and a key service unit by the use of transmission lines one-to-one corresponding to the individual key telephone sets, and in which the information between the key telephone sets is transmitted using a serial signal format of a frame configuration so that time slots of respective frames are synchronized with respect to all of the transmission lines.

Control signal transmission system for key telephone system

A synchronization system for a key telephone system, in which key information or the like information signal between a key service unit and each key telephone set is transmitted in the form of a time-division pulse signal under the control of a counter provided in the key service unit. The information signal has a format which is divided into a first signal from the key service unit to each key telephone set and a second signal from each key telephone set to the key service unit so as to make distinction between the first and second signals in terms of time. The first signal is disposed in a time slot preceding the second signal to provide a pair of signal groups. A one-pulse start signal is disposed in the foremost time slot of the signal groups and a one-pulse answer signal is disposed in a time slot between the first signal and the second signal.

Synchronization system for key telephone system

In a key telephone system including an electronic speech channel switching network and an electronic key telephone set selectively connected to central office lines by the speech channel switching network, the speech channel switching network is constituted by a pair of incoming lines connected to a pair of central office lines and a plurality of pairs of outgoing lines connected to the key telephone set. The incoming and outgoing lines are arranged in a matrix, and a plurality of controllable unidirectional switching elements are disposed respectively at four cross-points between the incoming and outgoing lines. Each switching element is connected oppositely with respect to one incoming line and to one outgoing line which comprise a pair.

Growing community of inventors

Yokohama, Japan

Kazuyuki Yamamoto