Patent GB-645303-A (GB)
Title: Improvements in or relating to telecommunication exchange systems
IPC: H04Q3/42
Filed: 1948-04-26
Abstract: 645,303. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. (Bell Telephone Manufacturing Co. Soc. Anon.). April 26, 1948, No. 11425. [Class 40 (iv)] In a system in which calls have to be routed through different countries, the originating exchange is equipped to recognize two proceedto-send signals, the first or '' international " signal causing it to transmit country-identifying digits and the second or " national. " signal causing it to send the digits identifying the called party within that country's system, each set of digits being also accompanied by the identity of the country of origin of the call. The two proceed-to-send signals may be common to the whole of the international system or may instead consist of the identity on the exchange reverting it, the register at the originating exchange being equipped to recognize whether the wanted country has been reached. By this method each intermediate exchange can obtain a record of the originating and wanted country and the originating country a record of all the intermediate countries. In cases where incoming operators have to handle calls the reception of the identification signal of the originating country may be used to ensure selection of positions manned by operators speaking the appropriate language. As shown, the operator at the originating country seizes an international keyset register IKR to which she sends first digits denoting the wanted country, then digits identifying the called subscriber within the country and finally an end of sending signal. On receipt of the last an outgoing line is seized in the required direction and if the line terminates in the wanted country a " national " seizing signal is sent forward which on receipt by VF equipment VFE associated with the incoming toll line circuit ITLC causes the seizure of a " national register " NR. The latter reverts " national " proceed-to-send signals to initiate the sending by the originating key-set register of each of the digits identifying the called subscriber within the national network until the key-set register sends an end-of-sending signal. When the final selection has been effected an end-of-selection signal is reverted to release the originating key-set register. If the outgoing line seized at the originating exchange terminates in an intermediate country (either because no direct lines exist or owing to the use of an overflow alternative routing scheme) the key-set register sends an " international " seizure signal which on receipt by the VF equipment associated with ITLC causes the seizure of a transit register TR which reverts the " international " proceed-to-send signal, whereupon the key-set register transmits the country identification digits to cause the seizure of an outgoing line in the required direction. A forward seizure signal of the "national" " or " international " type is then transmitted forward by the intermediate exchange according as the next exchange is in the desired country or not, the transit register is released and the VF equipment made unresponsive to all except clearing signals. The call then proceeds in a similar manner to the appropriate one of the two cases described above. Signalling. A four-unit binary code giving sixteen signals in all is used, ten being required for digits and the remainder for supervisory, &c. signalling. The end-of-sending signal renders the VF equipments unresponsive to any further numerical signals. The end-of-selection signal is used to give visual indication to the originating operator. In addition to the calledsubscriber-answer signal backward supervisory signals are also sent indicating if the called line is busy or idle for effecting the connection of the national ringing or busy tones at the originating country. The through speech paths are disabled during this interval to prevent unwanted intrusion of the foreign country's tones into the originating country's network. If the system of the called country does not normally provide an electrical condition indicative of the busy or idle condition of the called subscriber the national register NR is equipped with apparatus for recognizing busy and ringing tones and producing electrical signals in response thereto, release of this register being delayed until such signals have been reverted. The called-party-answer signal may be used to start a chargeable time computer in the originating country in the case where automatic ticketing is used. When the called party hangs up this is signalled to the originating operator who on receipt of the calling party clear sends a forward release signal to initiate break down of the connection. No release takes place thereupon but each incoming toll line circuit thereupon reverts a release guard signal at the end of which the outgoing and incoming ends of each line are released simultaneously.