840 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1952 



of built-in capability to perform quickly the circuit .selection work as- 

 sociated with the alternate routing features of the switching plan. In 

 adflition, to help provide the ti'aiismission margins needed for satisfac- 

 tory operation of the plan as contemplated, it must be arranged to con- 

 nect circuits on a four-wire basis rather than on a two-wire basis, the 

 latter being the an-angement used at most toll centers. The switching 

 ecjuipment at a CSP must not only pro\'ide for connecting one toll cir- 

 cuit to another; it must also perform the very important function of 

 tying the toll networks which sei've limited local areas together so that 

 collectively they work as a smoothly functioning nationwide system. 

 This becomes practicable when there is coordination between the design 

 of the individual limited networks and the design of the overall system. 

 The location of control switching points indicated by the nationwide 

 plan is shown in Fig. 7. This also indicates the home switching center of 

 higher order associated with each switching point. As the number of 

 CSP's increases, the cost of the toll circuit plant decreases because each 

 CSP can then be located closer to the cluster of ordinary toll centers 

 which it ser\^es. How^ever, because of the cost of the CSP eciuipment, it 

 is necessary to weigh the cost of circuit facilities with the ecjuipment costs 

 in a way that will result in the minimum overall cost. Certain of the 

 smaller Primary Outlets are being studied with the view of reclassifying 

 them as Tandem Outlets (TO's). A Tandem Outlet occupies the same 

 relative position in the switching plan as a Primary Outlet but is not a 

 control switching point. The switching equipment employed is less 

 complex than that used at control switching points and therefore pro- 

 vides for only limited alternate routing and does not have all the ad- 

 vantages of four-wire transmission. 



Effects of Customer and Operator Toll Dialing 



Customer dialing of short-haul toll calls has been in use, particularly 

 in metropolitan areas, for some years. A trial of long-haul customer 

 dialing over the intertoll trunk network and through the switching equip- 

 ment provided for operator toll dialing was instituted at Englewood, 

 New Jersey, in the Fall of 1951. The local ecjuipment includes automatic 

 message accounting and permits Englewood customers to dial directly 

 to about eleven million telephones in ten metropolitan areas across the 

 country. A trial installation of customer toll dialing, utilizing automatic 

 message accounting eriuipment on a centralized basis rather than at each 

 local office, is planned for Washington, D. C, in the Fall of 1953. Ini- 

 tially customers will dial toll calls within the Washington metropolitan 



