DEVICE FOR CONNECTION OF LONG-DISTANCE PUBLIC PAY TELEPHONES TO AUTOMATIC LONG-DISTANCE EXCHANGE STATIONS Russian patent published in 1998 - IPC

FIELD: electronic communications. SUBSTANCE: user side of device has public pay telephone, which is connected to automatic long-distance exchange station through user line, counter, secret key encoder and transmitter. Exchange side of device has interface set, user set, locking gate, search steps unit, rate pulse generator, receiver of tone signals, secret key decoder, counter and comparison circuit. Exchange station is connected to automatic long-distance exchange station through leased line. Device provides possibility to compare secret keys which are generated by counting rate signals at user and exchange station sides and encoding of secret key which is transmitted to exchange station through user line. EFFECT: protection against free long-distance calls by connection of unauthorized telephone devices. 3 dwg