GB1023476A - Circuit arrangement for interim connections in telephone private automatic branch exchanges - Google Patents

Abstract

1,023,476. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. July 5, 1963 [July 11, 1962], No. 26829/63. Heading H4K. In a cross-bar PABX provided with facilities for interim calls, initiation of such a call by an extension engaged in an outgoing call causes the extension to be connected, through an interim call circuit connected to the subscriber's side of the outgoing-call feedbridge in use, to a free feedbridge and register in which the identity of the interim party is recorded, whereafter the interim call is completed through the original feedbridge. In response to an extension N1 operating his " call back " key whereby both line wires are earthed, differential relay X comes up followed by UA thereby connecting N1 to a call-back circuit R-TS. When the key is released, UB is energized in series with UA(II) and R operates in series with A. Consequently starting potential is applied via r5 to initiate operation of a local link hunter AS. Relay C responds to the first free local link (feedbridge) JUe having an associated idle register, J-Reg to stop the hunter and operate relay T(II). The number of the interim party is dialled into the register which then selects the wanted line N2 and operates switching relay AA in the usual manner. Relay UC follows via bank d of the hunter AS, in order to release UA and maintain closed the main exchange loop Amt. The extension N1 is now connected via the original feedbridge AUe and the link JUe to the interim extension N2. In the event that N1 wishes to make an interim call to a main exchange subscriber, the register J-Reg brings up KZ followed by CC to release the local link and relay C and to operate UE(III). When the link is finally released, T and UE (windings I) hold and via their contacts t3, Ue4 they initiate operation of a trunk selector AW2. When the number of the wanted party is recorded in the trunk register A-Reg, relay D comes up to switch through extension N1 to the main exchange and to operate UC as before. The interim call may be released at any time by re-operating the call-back key whereby UD(I) and T(I) come up and R releases (some of these relays may already be in these states depending upon the progress of the interim call). When the key is restored, T falls first and UE comes up momentarily to release UA or UC, UB falling back when UE drops back. If an idle feedbridge and register are not available for use with the interim call, the subscriber is apprised of the situation by the lack of dial tone and then releases the interim call as described above.