GB642524A - Improvements in or relating to long distance tele-communication systems - Google Patents

Abstract

642,524. -Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Jan. 18, 1946, No. 1827. [Class 40 (iv)] In a long distance telecommunication system of the type using V.F. signalling, numerical switching, e.g. at a tandem exchange, is carried out under control of a signal, which may be the seizing signal, sent prior to the reception over the trunk of a proceed-to-send signal. Where several types of register are available for different classes of call, the reception of this signal determines which type, if any, is required, and may also control the transmission over an outgoing trunk of a further signal characteristic of a selection to be performed at a further exchange. A code is employed using two frequencies only in which each signal comprises one or two pulses, each of one or other or both of the frequencies. As shown in Fig. 1, a connection is set up in well known manner from a subscriber served by an international trunk exchange TE1 1 to an operator who takes into use the outgoing signalling circuit OGSC of the trunk leading to a tandem trunk exchange TE2 and controls the selection of the terminating trunk exchange by a key set OKS, operation of which causes AR to select an idle trunk and transmits a combined seizing and selecting signal to the signal circuit RTSC at TE2 which controls the switch BR to select one or other of the outgoing trunks ITA, ITBC, no register being required. If ITBC is selected, RTSC also controls the transmission of one of a plurality of seizing and selecting signals to TE3, in response to which ISC connects up a register REG by the switch DR and controls the selection by CR either of a trunk TB to a local selector train LST or to a group of outgoing trunks ITC. If the call is local a proceedto-send signal is reverted over the trunk to TE1 and the connection is then completed in well known manner. Outgoing termination equipment, Fig. 2. Operation of one of the keys KA, KB or KC by the operator at TE brings up AA, AB or AC followed by AE, whereupon AR hunts for an idle outlet to which AT operates, ATT coming up to connect an A.C. signal to the outgoing trunk over contacts of AA, AB or AC during the operate period of AD which switches through. Equipment at tandem exchange having no facilities for routing calls to a local area, Fig. 3. Operation of one or other or both of the relays BRA, BRB to the seizing signal brings up either BA, BB or BC, followed by BE, and BR hunts over either wiper 3 or 4, i.e. in the groups ITBC or ITA, according as BB or BC, or BA is operated. A seizure signal is sent forward over the trunk over relay BTR under control of BTT, the signal sent being dependent on which of the relays BA, BB, BC is operated. Equipment at tandem exchange having facilities for routing calls to a local area, Fig. 4. Operation of CRB results in the association of a local register and the backward transmission of a proceed-to-send signal, while if CRC is operated the call is extended to a distant office and a seizing signal is retransmitted as in Fig. 3. Operation of CRB is followed by that of CB-CE and CA, whereupon CR hunts for an idle outlet and the finder DR associated with a free register hunts for the line circuit, DT and CF pulling up in series on finding. The latter relay sends a proceed-to-send signal during the operate time of CFF. Relay CFF transfers the impulsing contacts of CRB, CRC to the register and further incoming V.F. pulses operate CRB and/or CRC and the digits are stored in the register, the DW relays pulling up to extend the pulsing circuits after each pulse. Translation or direct sending of the digits takes place in known manner, CG opening the forward loop for each impulse. If desired, the operation of CRC may be used to introduce a second register in the same way as CRB associates the first.