Patent GB-651604-A (GB)
IPC: H04W4/00
Abstract: 651,604. Automatic exchange systems. GENERAL ELECTRIC CO., Ltd., COLLYER, J. E., and FAIRBAIRN, E. P. Sept. 9, 1948, No. 23721. [Class 40 (iv)] In a telephone system consisting of a number of automatic exchanges connected by radio links, the encountering of a busy condition during the setting up of a call causes the release of all the radio links already seized unless the subscriber has priority facilities which enable him to break into an existing connection by dialling an extra digit after receiving busy tone. The invention is described in respect of a single intermediate exchange in which the line-finders are controlled by combined allotter registers, the first digit dialled determining the connection either to a radio link or to a local subscriber through final selectors. Incoming call from local subscriber. Operation of the line relay L, Fig. 3, marks the calling line on finder bank LF4 and pulls up seriesconnected allotter start relays ST, Fig. 4. Two allotters are normally provided, one being shown, and a busy allotter is isolated by a shortcircuit connection across its start relay controlled by relay CT. The allotter switch hunts until an idle finder is found, when relay DK pulls up and disconnects the drive magnet AL. Relay DR starts the line-finder and relay DS connects the allotter to the first selector, Fig. 5. When the line-finder locates the calling line, relay FK pulls up and applies busy earth. The calling line is then extended to the first selector by relay KF, which also earths the appropriate P wire and pulls up relay K to disconnect the start signal and remove earth from the calling line. Relays DR and DK fall back and BA, SW and CT operate over a circuit including a contact CO2 located in the register. Relay CT disables the start relay and SW causes dialling tone to be induced in the calling line over the impulsing relay LA. Relay LA and repeating relay L in the allotter pull up' followed by dialling relay B, and the impulses are repeated to the register (not shown) over lead 22. During registration, the register operates relay AA over lead 23 and slow release relay CA pulls up over a high-resistance winding without operating the first selector magnet S. Translated digits from the register arrive on lead 23, and the first break from earth releases AA, thereby operating magnet S over a low resistance winding of CA. Relay AA then repeats each impulse of the first translated digit and the first selector steps to a final selector group or to outgoing trunks to a radio link. Relay AA remains operated at the end of the digit so that CA falls back, and the selector hunts for an idle trunk in the group required until relay H pulls up over bank S3. Relay H busies the outlet, and HR extends the speech conductors and lead 23 over the first selector. Further impulses from the register then either position the final selector or are repeated by a switching device (not shown) for transmission over a radio link in one of two directions determined by the setting of the first selector. After all the stored digits have been transmitted, register contact CO2 opens and an earth is applied to lead 21. The register and allotter are then freed by the release of relays CT, SW, A, B and DS. When the called party hangs up, LA falls back and BA, Hand HR are released. Of the switches shown, the first selector only returns to its home position. All final selectors busy. The first selector stops on the last outlet in the group, the corresponding homing contact in bank S6 being unmarked. Relay OV operates over bank S7 and connects busy tone. Local called party engaged. Before the register and allotter are freed, a test in the final selector operates BY over bank S5 if the called line is engaged. Relay OV connects busy tone and the speech conductors are disconnected from the first selector by the relapse of relays H and HR unless the calling subscriber has priority facilities, in which case H and HR remain held. Breaking-in facilities of priority subscribers. Each priority subscriber has an earth connection to the appropriate contact in line-finder bank LF3. On receiving busy tone the subscriber dials the digit " 1 " and the impulse is repeated by LA. Relay R pulls up and locks to the priority earth, thereby disconnecting busy tone. If the final selectors are busy, relay HR operates to extend the speech conductors to an engaged selector. If the called party is engaged then the impulse is repeated over bank S4 to the final selector where it operates a switching relay to break into the established connection. Calls extending over radio links. Each radio link. includes switching devices (not shown) which comprise circuits similar to those provided in the first and final selectors, the seizure of a switching device causing emission of carrier over a link. Subsequent impulses, signals and speech are repeated over the link by the switching devices and the encountering of a busy condition at any stage in setting up causes the switching device to function as though it were a final selector positioned on a busy subscriber, busy tone being returned to the originating exchange so that relay BY operates unless the subscriber has priority. Similarly if a connection to a busy subscriber via radio links has been made, the links and apparatus already in use are only held by the originating exchange if the subscriber has priority. In the intermediate exchanges, through connections between radio links are provided over singlemotion switches without the call traversing the first and final selectors, the switching devices being provided in both the incoming and outgoing lines.