Patent GB-1379445-A (GB)
Title: Dial pulse incoming trunk and register arrangement for a communi cation switching system
IPC: H04Q3/545
Filed: 1972-03-08
Abstract: 1379445 Automatic exchange systems GTE AUTOMATIC ELECTRIC LABORATORIES Inc 8 March 1972 [9 March 1971] 10894/72 Heading H4K In a system having a centrally controlled exchange to which calls are extended over junctions from step-by-step offices, the junctions are provided at their incoming ends with an impulse absorption facility so that delay in attaching a register to the junction can be accommodated. The control circuit on detecting a calling line or junction determines its nature viz dial pulse, MF, local line, party line, coinbox line or incoming junction and informs the chosen register accordingly. Subsequently during digit reception the register utilizes this information so as to appropriately respond to a special signal condition transmitted over the switching network path between the line/junction and the register. In the case of an incoming dial pulse junction the condition, e.g. an earthed + wire, signifies that one impulse of the first digit has been absorbed. General description.-The system provides a single switching network 111 for interconnecting any type of "line" circuit with separately provided registers and senders under the control of a stored programme processor CP. The "line"  circuits may terminate local single L1 or two party L2 lines 1 parties being distinguishable by an earth on the + wire), coinbox lines CB (coin insertion being signalled by earth on the + wire), incoming trunks IT and outgoing trunks OT. Dial pulse and touch calling digit transmission is accommodated. Each line circuit is coupled to selection of ring. cores which provide line identification and class of service data. The cores are scanned on a group basis, a group only being entered if a change of state for at least one member of the group is detected. Central control in response to class information advises a selected register as to the meaning it should place on similar signalling conditions, i.e. one leg earthed, and also advises it as to the number of digits that should be received before a register calls or recalls the central control into service. Particular description.-In response to a loop on an incoming junction from a Strowger exchange, relay CS (Fig. 13), in the junction terminating circuit comes up after 10 msec, so as to close another loop via a 500 # resistor towards the line circuit (i.e. network appearance circuit), for this junction. Relay L follows after a further 10 msecs, so as to send a request for central control's services via the group station circuit. The latter is scanned on a regular basis via the logic CPN so that central control on detecting a calling group can enter the group and identify the particular calling line/junction. Central control then takes at least 92 m.secs to process the request and to connect a register input circuit (Fig. 12), via the switching network R, RA to the calling line circuit. In the register a dial tone relay is normally brought up as is a register busy relay B and follower BB, B causing a holding earth to be reverted over the C wire to the calling line circuit. In the case considered however, DT is not energized but impulse repeating relay A is energized over the 500 # loop on the speech wires from the calling line circuit. The C-wire earth operates cut-off relay CO in the line circuit so as to release the line relay, bring up lock-out relay LO and actuate relay CR in the junction circuit. Meanwhile the first impulse of the first digit from Strowger may appear 50 msecs, after seizure of the junction so causing CS to fall back. Two step relay RS responds by closing RS1 so as to prepare for full operation thereof when CS reenergizes at the end of the impulse. With RS full on the incoming junction is cut through to the line circuit and thus to the register if this has by now been connected. Subsequent impulses of the first digit are applied to the register directly. In addition RS<SP>1</SP> replaces the 500 # loop with a 1000 # ground on the + wire thereby signalling to the register that it must increment the number of further impulses by one in order to store the first digit properly. On the other hand if a register had not been connected, the restoration of CS in conjunction with an operative relay B (which takes 200 m.sec. to release), would complete an energization path for relay BT. The latter takes 40 msec. to come up so that if CR does not operate within this period then a busy tone source will be connected via windings of CS to the junction by the relapse of RS. CR is disabled by the operation of BT so as to prevent its operation should a register be connected subsequently. Provided CR operates in time however the subsequent falling back of B removes the 1000 # ground on the + wire and the call proceeds. Digit reception.-When the register is connected to the junction, relay A comes up so as to ready the register's logic and to start a 15 sec. timer. If the latter times out, a request is made to central control for the provision of a busy tone command, this being effective on relay BT which thus connects a busy tone source through the A relay to the calling junction. As impulses arrive however the timer is reset and the impulses are repeated by A via a transistor impulse correction circuit (Fig. 11, not shown), to a set of four flip flops forming the first stage of a multi-stage shift register (Fig. 9, not shown). Each pulse, i.e. loop open, is effective on a 300 msec. times which causes the call to be abandoned if it times out. In the case considered the register knows that it is connected to a dial pulse junction so that when a polarized relay D comes up to the 1000 # ground on the + wire it immediately increments the flip flop counter to allow for the absorbed pulse. When the time between pulses exceeds 100 msec. an interdigital pause is assumed and central control's services are requested unless a command to wait for more than one digit has been given. As each new digit is received the contents of the register are shifted into flip flops of an adjacent stage. Multi-frequency signals are received in a special receiver (Fig. 12), which is connected in parallel with the digit repeating portion of the register input circuit.