In-BandSingle-FrequencySignaling-TheHistoryofPhone.PDFVIP

In-Band Single-Frequency Signaling By A. WEAVER and N. A. NEWELL (Manuscript received June 7, 1954) Single-frequency signaling liberates dial systems from the restrictions of dc signaling methods. This freedom, as might be expected, is most important in the long distance telephone plant where trunks are .frequently too long or have no conductors .for dc signaling. The general plan of signal frequency (SF) signaling is based upon continuous signaling because of it’s speed and reliability. In this respect it is like the usual dc trunk signaling schemes. SF uses steady current in the trunk signaling path for the normal idle trun]~ condition and no current in the signaling path .for the other a~ alternate b~sy (talking) trunk condition. This choice of signal conditions is essential for SF signaling in-band systems, which as the name implies operate within the standard voice channel, to avoid conflict between signal and voice trans- mission. The same conditions are also used in SF out-of-band and separate line systems. The in-band SF system can be used with any type or length q~ line.facility that meets nor~nal voice transmission requirements and is there.fore the pre- ferred method used by the Bell System to meet requirements for toll dialing on a national basis, with Other signaling arrangements limited to the shorter trunks. The requirements, design considerations, main .features, and method of operation .for the in-band system are outlined in this paper. INTRODUCTION The signaling requirements for dial telephone operation are naturally more exacting than those for manual switching methods. This means a high order of signaling system is needed to satisfy the requirements for the toll ~elephone plant and for automatic toll switching systems de- scribed in recent papers in this JO~JRNAn), ~ Indeed the advantages in speed and economy of dial telephone systems depe