SYSTEM WHICH COUNTS DURATION OF TELEPHONE TALKS

FIELD: electric communication, in particular, limitation of duration of telephone conversations and payment for excess time using standard rate. SUBSTANCE: Device uses code of total time of telephone conversations as protection number which is encrypted and transmitted to telephone exchange when connection between users is established. Telephone exchange system decrypts source value and compares it to corresponding number which is calculated by exchange computer. User part of device has user counter which is connected to customer loop 13 and has interface unit 1, power supply unit 2, connection-type analyzer 3, control unit 4, first digit detector 5, tonal signal detector 6, electronic indicator 7, oscillator 8, divider 9, electronic counter 10. In addition device has encryption unit 11 and transmitter 12 and corresponding connections. Customer loop 13 is connected to telephone exchange which has electronic gate 14, subscriber's line equipment 15, commutation equipment unit 16, computer 17, receiver 18, encryption unit 19, first and second shift registers 20, 21 and comparison circuit 22. EFFECT: protection of customer loop against unauthorized connection of foreign telephone sets and possibility for subscriber to check duration of telephone conversations. 2 cl, 2 tbl, 3 dwg