FUNDAMENTAL PLANS FOR TOLL TELEPHONE PLANT 847 



hutsy sifijnals which arc (>sscntial to the efficient operation of the switchiuf^ 

 phuit. 'fhc circuit (lesi<>;ii conleinphited in the o\'erall plan must tafvc 

 into accouni this rc(iuircnicnt lor tiansniit tina; sii>;nafs as well as speecli, 

 to ol)tain a< 'curacy and speed in set t int; up and takinu; (h)wn connections. 



TKANSMISSIOX DESIGN ASPECTS OF CIUCUITS FOR NATIONWIDE 

 TOLL DLVLING 



'\l\o more extensiyp use of alternate I'outins to<2;ether with the increase 

 in maximum possible number of trunks in tandem associated with nation- 

 wide toll dialing, tends to increase the problems of assuring adequate 

 transmission of speech and signals on all possi])le connections. On the 

 other hand, the use of four- wire switching at important points and the 

 definiteness of the routing patterns permit more efTectiye use of the 

 ayailable facilities and thus tend to simplify the problem. Extensive 

 studies indicate that on the whole, the new toll switching plan will make 

 feasible still further improvements in transmission. This is, of course, a 

 desirable objective. 



Tranf^mission Design of Tnmks 



With dial operation, the number of trunks in tandem in a given toll 

 connection may vary on successive calls. To avoid undesirable trans- 

 mission contrasts and other adverse effects, it is important that every 

 trunk be designed to operate as closely as possible to the theoretically 

 correct transmission loss. The problem is complicated by the fact that 

 the extent to which the echo, noise and crosstalk will limit the perform- 

 ance of an individual link is not directly proportional to the length of the 

 circuit. In fact, the minimum loss at which a particular circuit used 

 singly or in various built-up combinations can theoretically be operated 

 depends on the number, length and characteristics of the other circuits 

 connected in tandem with it. Arrangements for precisely adjusting the 

 loss in the indi\'idual trunks for each call would be complicated. Adequate 

 performance can be achieved however by compromise methods Avhich 

 provide for automatic adjustments in the loss of each trunk in accordance 

 with the following: 



1. When a trunk is switched to other intertoll trunks at both ends it 

 is operated at the minimum loss practicable. This loss is known as "via 

 net loss." (VXL) 



2. When the trunk is switched to another intertoll trunk at one end 

 only, the loss is increased two db. 



3. When the trunk is not switched to another intertoll trunk at either 



