GB1077473A - Improvements in or relating to automatic telephone systems - Google Patents

Abstract

1,077,473. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. April 6, 1965, No. 14471/65. Heading H4K. To meet the demands of increased traffic or the modifications consequent on the adoption of a National Dialling Scheme, an existing exchange employing rotary power driven revertively controlled switches is augmented by a cross-bar exchange using self-steering techniques. The scheme illustrated shows in Fig. 1 part of the rotary exchange in which 15 normal line finders 1LFN connect a calling line to a so-called cord circuit CC unless, in conditions of peak traffic, all but one of these line finders is employed when the connection is made by 5 first line finders 1LFP and second stage line finders 2LF. To each cord circuit there is a trunk access circuit TAC1 which calls upon the services of a register RREG by way of link circuit LC containing register and group selector finder switches. If a call requires connection over the cross-bar trunk exchange CTE, to the right of Fig. 2, the dialled code starts with digit 9 and causes the register RREG to put positive battery on the C-wire to operate relay LR in cord circuit CC. The cord circuits are connected to outlets of a two-stage cross-bar distributer DSA1, DSB1 providing connection between a cord circuit, marked as calling by earth from a marker LMKR (not otherwise shown) when relay LR operates, and a relay set of a junction relay group OJRG of the crossbar trunk exchange. The earth mark from CC on lead N operates select magnets in preparation for the operation of bridge magnets, and free links LKS to which the marked outlet has access are marked. In each selector in the stage DSA1 having a marked link LKS at least one select magnet is marked by the operation of a control relay which also initiates forward marking from outgoing junction relay groups OJRG available to the DSA1 selector. Test relays in the stage DSA1, in conjunction with marker LMKR, select an available group OJRG and, on operating the associated select magnet and bridge magnets, set up the wanted connection over the distributer. In the cord circuit relay K responds over the P wire, releasing the register RREG and the marker LMKR. In the cross-bar trunk exchange an incoming trunk relay group ITRG is seized and a register CREG is taken into use to receive subsequent digits from the calling subscriber.