NATION W I I)K Al TOM A'l'IC SWITCHING 825 



cess of the No. 4 installation at Philadelphia, led to studies of the 

 service and operating results which might l)e expected from a nationwide 

 extension of automatic switching. The conclusion was reached that this 

 would be a desirable obj(M-ti\'e of the Hell System companies and would 

 r(>sult in a \-erv substantial fui'thei- improx'ement in the spewed and ac- 

 curacy- of handling of long distance messages. Accordingly, during the 

 next few years, a national plan was pi'epar(>d and was adopted by the 

 telephone companies. 



OKXKHAL PLAN FOK NATIOXW IDE AU'roMATIC SWITCHING 



The features of this nationwide plan and the present status of its 

 application form the subject of the three technical papers which accom- 

 pany this introductory paper. ' ' " The basic requirements to be met 

 in the development of this plan included the following: 



1. It should be suitable for the nationwide extension of automatic 

 switching both by originating toll operators and by the customers direct. 



When this work was commenced it was clear that a program leading 

 toward general nationwide operator dialing was desirable. Subsequent 

 de\elopments have confirmed the wisdom of making the basic plan 

 consistent with general nationwide customer dialing as well since it now 

 appears that a very wide extension of this form of service wall become 

 desirable. 



2. The plan must provide for satisfactory overall service betw^een 

 any two telephones in this country and Canada. 



I'^nder manual operation satisfactory overall service was provided 

 for by the general toll switching plan in use since about 1930. This plan 

 is modified to recognize the far greater speed and accuracy of automatic 

 switching compared with manual swit(;hing. This involves also modifi- 

 cations of transmission design standards so that the overall connections 

 will continue to be satisfactory. 



3. The system must be designed for instantaneous service, so that 

 delays due to lack of circuits or equipment would be very infrequent. 

 This is necessary, both from the standpoints of service and the avoidance 

 of tieups, particularly of the automatic switching machinery. 



A trunking system must therefore be devised which will most economi- 

 cally meet this I'equirement, considering overall costs of lines, switch- 

 ing equipment and operation. 



4. Machines must be designed for use at strategic points in the net- 

 work, called "control switching points", to perform automatically the 

 various tasks required to make the overall plan operative and economical.. 



