Nationwide Dialing

One of the first problems of nationwide dialing is the selection of a numbering scheme whereby the operator can reach any particular subscriber without conflict because local numbering of subscribers in different towns is the same.¹¹ Before investigating a possible numbering scheme, it is necessary to examine the numbering on the dial itself. The following numbers and letters are found in the ten holes on the standard telephone dial.

Letters - ABC DEF GHI JKL MNO PRS TUV WXY Z Numerals - 1234567890

From this it will be noticed that the letters used in office names appear in only eight of the holes on the dial. The first position is avoided because of the possibility of a single digit being transmitted by a "fumble" of the switch hook, thus giving a wrong number. The "0" position is reserved for dialing the operator with a single pull of the dial. For toll dialing purposes, it is proposed to set up numbering areas on a basis similar to that used for choosing office codes in local systems, but in such a way that it will not interfere with the method of dialing local calls.

In New York, for example, it was necessary to assign numerals instead of letters to the third digit,¹¹ therefore using only the first two letters of the office code such as ADams-2, or BEacon-3, or even ADams-2 and ADams-3. Under this method of assigning office codes, it is possible theoretically to have 8 X 8 X 10 = 640 local offices in a single numbering code area, and, with each office having 10,000 lines, the capacity of each numbering code area would be 6400000 subscribers. This is only theoretical, however, and actually the number per area will be considerably fewer than this figure because many offices have far less than 10,000 lines and because there are only approximately 500 office codes that are useful. It has been estimated that between 50 and 75 numbering code areas will be sufficient to serve the United States and Canada and that this would handle many times the present total of about 40,000,000 telephones in these two countries.

For dialing purposes, the United States may be divided by states in some regions and by groups of two or three states in others, and the more thickly populated states may be divided into two or three numbering code areas.¹¹

Each area will be handled on a seven-digit basis, and two digits will be required for the toll code, giving a total of nine digits which will be sufficient to give every telephone subscriber a toll number without interfering with the local numbering. For calls within the same numbering code area, seven digits will suffice, but on calls to other areas it is desired for routing purposes to have something to distinguish this call from a local call. As already pointed out, neither the "1" nor the "0" appear in the first two digits of a local office code, therefore if a "1" is inserted as the second digit, the code for a call to area "65" would be "615." This makes ten the maximum number of digits required for nationwide dialing.

In reference 11, which considers the preceding matters in detail, nationwide dialing with step-by-step equipment and with crossbar equipment are compared. It is shown that with the use of crossbar toll-switching equipment nationwide dialing, using the ten-digit code, is a definite possibility. It will, no doubt, be some years before this plan is in effect, although at present (1949) the groundwork has been well laid.

(1)	Material for this section was prepared by Mr. Dwight L. Jones. (See preface.)