444 



BELL SYSTEM TECHNICAL JOURNAL 



operating equivalent for an intermediate link. Four-wire circuits 

 equipped with echo suppressors are unique in that at the longer 

 circuit lengths the increase in minimum net equivalent with further 

 increase in length becomes very slight. 



Two general arrangements for removing the switching pads from 

 and restoring them to the toll line circuits are available depending 

 upon the type of switchboard facilities involved. Either arrangement 



PO 



3 3* is> 



iVVV^Wp 



QNGC 



■ TC 

 «v 



SAME AREA 



DISTANT AREA 



DISTANT AREA 



Wr| DISTANT AREA 

 PO 



INTRA AREA 

 TC 



(3)[-0 



SAME AREA 



■"PO 



TC=TOLL CENTER 

 P0= PRIMARY OUTLET 

 RC= REGIONAL CENTER 

 NGC = NON-GAIN SWITCHING 

 CENTER. 



( ) MINIMUM WORKING NET LOSS MAXIMUM TOLL CIRCUIT EQUIVALENT I 7 db 



O OPERATING VIA EQUIVALENT MAXIMUM OVERALL CONNECTIONS 3ldb 



[] TRANSMISSION MARGIN ASSUMED LIMITING TOLL TERMINAL LOS5--7db 



*VALUE or PAD IN TERMINAL LINKS DEPENDENT ON NOISE AND CROSS-TALK CONDITIONS 



Fig. 11 — Diagrammatic representation of transmission data for handling switclied 

 toll traffic under general toil switcliing plan. 



requires the modification of both the toll line circuit and the switch- 

 board circuits. One method controls the switching pad by a marginal 

 relay in the sleeve of the toll line circuit. In the other arrangement, 

 the pad is under the control of relays operated by battery supplied 

 from a simple.x bridge in the connecting circuits. 



With the general toll switching plan the number of places in which 

 switching gain is required is greatly limited, being, as pointed out 

 above, a total of about 150 out of 2,500 toll centers. This number 

 will be somewhat increased by secondary switching points in which 

 it is found economical to insert switching gain in order to save the 

 back-haul involved in following the routing provided by the plan. 

 However, the net result is that under the toll switching plan the number 

 of points at which switching gain is provided will be materially 

 limited, with corresponding economies. 



