Automatic Toll Switching Systems

A plan for automatic long distance switching, which will ultimately embrace the entire area of the United States and extend into Canada and perhaps Mexico, has been formulated and important steps have been taken toward its realization. The plan contemplates that when a telephone customer places a call with a long distance operator, this operator will be able to establish a connection to any desired telephone simply by playing a 10 or 11 digit code into an automatic mechanism. She will receive distinctive signals when the called telephone answers or when the telephone or the toll circuits are busy. She will completely control the establishment of the connection and will have available to her the information necessary for proper billing of the call. The plan also contemplates that telephone customers will ultimately be able to dial long distance calls themselves, wherever may be the locations of the calling and called telephones.

Automatic Switching for Nationwide Telephone Service

Clark¹,

Osborne²

1952

Fundamental Plans for Toll Telephone Plant

Pilliod¹

1952

This paper covers the general switching plan and fundamental plant layout proposed for handling telephone toll messages throughout the United States and Canada using automatic toll switching. There has been rapid growth in the number of telephones and in the volume of toll traffic, particularly long haul. Toll facilities are provided under fundamental plans, an essential part of which is a toll switching plan for setting up connections quickly between any two telephones. The introduction of mechanical operation and the general improvement in the transmission performance of the communication plant over a period of years make the introduction of certain modifications in the fundamental plans possible and advantageous at this time. The important new features and the service improvements which are provided by the proposed plans are outlined in this paper. The principal types and characteristics of circuit facilities available for use in the intertoll network are also described.

In-Band Single-Frequency Signaling

Weaver¹,

Newell²

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 trunk condition and no current in the signaling path for the other and alternate busy (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 transmission. 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 of line facility that meets normal voice transmission requirements and is therefore the preferred 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.