Application of Multifrequency Pulsing in Switching

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.

Fundamental Plans for Toll Telephone Plant

Pilliod¹

1952

Automatic Toll Switching Systems

Shipley¹

1952

A new automatic toll switching system has been developed by the Bell Telephone Laboratories for use at the most important switching centers for implementing the nationwide dialing program. The job of performing the switching functions at such points is the most comprehensive ever performed by any system, requiring a high order of mechanical intelligence. The new switching system uses crossbar switches for the talking connections and fully exploits the common control principle whereby the equipment used for directing the establishment of connections through the switches is provided in pools common to the office and is used with high efficiency. To perform the complicated, translating functions a new device called the card translator has been developed. It uses punched metal cards and an optical system with phototransistors. Routing changes are made by insertion of previously prepared cards in the machine. The switching system was designed with the objective of handling long distance traffic dialed by customers as well as that dialed by operators.

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.