GB927338A - Improvements in or relating to telephone networks - Google Patents

Abstract

927,338. Automatic exchange systems. SIEMENS & HALSKE A.G. July 25, 1961 [July 25, 1960], No. 26898/61. Class 40 (4). In an inter-exchange system employing V.F. signalling, each supervisory signal is preceded by a preparatory signal which causes a common V.F. receiver to be taken into use at the receiving exchange. The preparatory signal is not necessarily of voice-frequency but is always the same. The junctions terminate in outgoing and incoming repeaters Ug, Uk which seize when required common V.F. transmitting and receiving apparatus TSEg, TSEk. The junctions L2, L3 may be 4-wire. Assuming a call between exchanges B and C, on the occurrence of a supervisory condition at B, for example, the preparatory signal is sent from Ug and TSEg is taken into use. The receipt of this signal at Uk takes into use TSEk which sends a V.F. acknowledgment signal. The latter is received in TSEg, cuts off the preparatory signal and causes the appropriate V.F. supervisory signal to be sent. This when received cuts off the acknowledgment signal which in turn cuts off the supervisory signal, and the common apparatus is released. The acknowledgment signal may be dispensed with, provided the preparatory signal is of limited duration. Different single frequencies are employed for different supervisory conditions. The system caters for a break-in signal from the calling end as well as for the usual reply and clearing signals. On a tandem call between A and D, for example, a connection between Ug and Uk at the intermediate exchanges B, C results in circuit changes by which the preparatory signal is repeated at those exchanges whereas the V.F. signals pass straight through, although the common apparatus is taken into use momentarily. The circuits of the repeaters Ug, Uk and of the common apparatus are described with reference to Figs. 1, 2 (not shown).