Patent GB-990823-A (GB)
Title: Time division multiplex telecommunication exchange
IPC: H03K17/64
Filed: 1961-08-04
Abstract: 990,823. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. Aug. 4, 1961 [Aug. 9, 1960], No. 28473/61. Heading H4K. In an exchange using a plurality of time division multiplex speech highways, groups of voice frequency transmitters or receivers are connectible to subscribers or to junctions by way of a highway particular to each group of transmitters or receivers and by way of intermediate highways linking the transmitter or receiver group highways to the speech highways serving groups of subscribers and junctions. The exchange comprises groups of 100 subscribers with line circuits such as LC 1 , LC 2 , served by highways such as GH 1'  GH 2 . Connections between one highway and another are made via intermediate highways such as IH 12 . Groups of incoming and outgoing trunk circuits, such as LC 0 , LC 1 , are served by highways OJ, IJ, which connect with subscribers via intermediate highways such as IH 13  and IH 14 . Groups of sender/receivers, of which SU is an example, are connectible to the junction and subscriber highways by means of intermediate highways IH 15 , IH 16 . The gates between highways and between highways and terminal equipment are controlled by slave storage devices of which SM 1  is an example so as to gate a multiplex channel at a time determined by circulating delay stores. The slave storage devices are set up by a common register REG which comprises a magnetic core matrix with as many rows as the total number of simultaneous calls the exchange will handle. Each row of the matrix comprises a register with all the pertinent information regarding a single call. The matrix rows are read cyclically so that the staticized information from each row may be brought up to date with changed conditions at least once every cycle. When a calling condition of a subscriber is detected the register scans the send/receive circuits SU for an idle one which it seizes and sets up a path between the unit and the subscriber. Such a unit is shown in more detail at the bottom of the Figure and can be seen to have a bi-stable circuit BS 4 , which is set 1 to mark the unit busy, and a bi-stable circuit BS 3 , which is set 1 to connect dial tone from a source OSC to the tandem connected highways over which the connection has been routed. Subscribers may have a dial which transmits D.C. impulses, in which event a call would use an appropriate send/receive circuit other than the circuit SU illustrated, or they may have a dial which transmits alternate tones as the loop opens and closes. In the latter event receivers REC1, REC2, in unit SU, alternately set self-restoring bi-stable circuits BS 1 , BS 2  to relay the loop condition to the register. As soon as the first impulse is recorded by BS 1 , BS 2  is reset either by the register, or by the dotted line connected capacitor, in order that dial tone should be disconnected. By scanning the bi-stable circuits BS 1 , BS 2 , of the signal circuit SU it has in charge, a row of the matrix REG may accumulate and record the identity of the wanted subscriber. Alternatively, the send/receive circuit may store the numerical digits of a wanted subscriber for transmission over a junction. By the provision of more bi-stable circuits and receivers the calling subscriber may send the wanted subscriber's number in two-out-offive code. If the first two digits received prove upon translation to require an out-going junction, such as LCO, such a junction is seized and a D.C. condition applied to the outgoing trunk to cause the distant exchange to seize a register and a six-frequency send/receive circuit. At the originating exchange a similar six-frequency send/receive circuit is seized and is connected over the highways to the outgoing junction circuit. The distant exchange sends a two-out-of-six frequency code as a proceed-tosend signal which is detected by the corresponding send/receive circuit at the originating exchange. When in possession of the remaining digits of the wanted subscriber, the register REG will release its first send/receive circuit SU by resetting BS 4  and will instruct the new six-frequency send/receive circuit to transmit the remaining digits over the junction. In response, the distant exchange returns the called subscriber's condition whereupon the originating exchange releases its send/receive circuit and proceeds either to set up the connection to the junction or send busy tone. Specifications 824,221, 904,232, 904,233, 904,234, 970,821, 971,802 and 977,420 are referred to.