Patent GB-1218344-A (GB)
Title: Improvements in or relating to private telephone exchanges
Inventor: SMITHERS RONALD
IPC: H04Q3/62
Filed: 1967-01-12
Abstract: 1,218,344. Automatic exchange systems. GENERAL ELECTRIC CO. Ltd. 12 Jan., 1968 [12 Jan., 1967], No. 1757/67. Heading H4K.  In a private exchange in which extension lines are connected over successive stages A, B, C of reed relay matrices under a common control 17, three types of supervisory units are employed, the first 6 serving for internal calls set up automatically, the second 7 for external calls, e.g. over tie-lines, and the third 8 for internal or external calls controlled from an operator's switchboard 11. Relay switches 13, 12 ensure full availability between the units 8 and both the units 7 and the switchboards 11. Internal call.-On the initiation of a call, line relay LR of the line unit sends a pulse to a Dimond ring-type coder 22 which supplies the  calling number to an allotted register 25. A decoder 28 operates relay LMK to mark the line and the common control 17 affects its connection to an idle extension supervisory 6. The dialled number is passed from the latter to the register 25, which operates through the decoder 28 and common control 17 to connect the wanted line to the same extension supervisory 6. If the call is to be set up by an operator, the receipt of the digit 0 in the register causes the transfer of the connection from the extension supervisory 6 to a service supervisory 8 and thence to the switchboards 11. An operator answers using any one of the five call control circuits on her switchboard, and the register 25 now receives the identity of the service supervisory 8 and the wanted number as keyed by the operator, and effects the desired connection. The operator can break in or withdraw completely from the connection. Outgoing call.-The caller obtains access to an operator as described above. The operator keys the number of the route required, an idle tie-line 9 is allotted and connection is made over switches 13 to the junction supervisory 7, and a register 25 receives the identity of the latter. The wanted party is rung, and after reply the operator can talk with either party. She may retain supervision or withdraw from the call, in which latter case a signal is sent back over the P wire to a Dimond ring-type line identifier 108 and associated register 28 to effect a direct connection through the A, B, C switches to the junction supervisory 7. Incoming call.-A route indicator lamp lights at each switchboard 11. When an operator answers, a service supervisory 8 is allotted and connected to the junction supervisory 7. On hearing the wanted number the operator keys it into a register 25 which completes the extension of the call, the operator retaining supervision or not, as in the case of an outgoing call. An incoming call may also be extended in tandem fashion over another route. Enquiry call.-When engaged in an external call, an extension party can make an enquiry call by actuation of an earthing button, the external call remaining held. An idle service supervisory is allotted and connected to a register and the enquiry call is set up by dialling. A second actuation of the earthing button breaks down the enquiry call and restores the external call. Moreover, if the first extension party hangs up, the external call may be transferred to the second party. An enquiry call may be made to an operator by dialling D.