System of active protection of the line

The System of Active Protection of the Line (SAPL) prevents deceptive use of public phone line from unauthorized access through parallel connection or a self-detachment of the line. SAZL consists of the Station Blok (SB) placed on a segment of automatic telephone exchange and the Subscriber Blok (SB) established on the payphone terminal. Interaction of the SAZL hubs (AB and SB) happens by means of transfer and reception of a personal code of identification. The identification code constantly automatically changes. Quantity of combinations of a code of identification not smaller as 28. Transfer of a personal code of identification happens after a payphone tube raising. When phone line is occupied, SB sends the message of AB, and if the answer wrong or is absent, - the line is separated and unauthorized conversation breaks.