ITU-T U 3-1988 ARRANGEMENTS IN SWITCHING EQUIPMENT TO MINIMIZE THE EFFECTS OF FALSE CALLING SIGNALS《国际电路交换公众电报网使用的信令状况》.pdf

1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 5 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU4%,%2!0(G0G037)4#().%.%2!,!22!.%-%.43G0G0).G0G037)4#().G0G0%15)0-%.44/G0G0-).)-):%G0G04(%G0G0%(b) that such false calling signals can seize and engage switching equipment, thereby reducing the grade ofservice

2、. This is of particular importance with systems in which common equipment normally used only to set up calls isseized by false calling signals;(c) that the ill effects of false calling signals can be minimized by delaying the operation of the calling relay atthe termination of the international tele

3、x trunk circuit;(d) that, however, when direct dial selection is employed over an international trunk line, unless it is amanually selected circuit not preceded by a stage of automatic selection, there is normally insufficient time availablebetween successive digits to permit the use of slow operati

4、ng relays;(e) that, nevertheless, Administrations may agree among one another to use digit storage at the outgoing end ofthe circuit so that the inter-train pause can be increased to permit the calling relays to be made slow to operate,unanimously declares the view(1) that the design and maintenance

5、 of transmission systems should be such as to reduce to a minimum thenumber and duration of false calling signals. In this connection attention is drawn to the merits of frequency-modulatedvoice-frequency telegraph systems, particularly with long overhead lines;(2) that, wherever possible, calling relays on international telex trunk circuits should have an operation lag ofat least 100 milliseconds. Administrations using circuits on lines prone to long-duration false calling signals may agreeto use calling relays with longer operation lags.