1034 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER, 1953 



is extended, the plant will become more homogeneous and the need for 

 such charts will gradually disappear. 



Fortunately, from the transmission standpoint, while the machines 

 will set up a wide variety of connections, the routing patterns will be 

 rigidly controlled. Thus, it is practicable to know for each circuit group 

 the maximum number of other circuits with which it can be used in tan- 

 dem. The lower velocity circuits, two-wire circuits, narrow band circuits, 

 etc. can (within practical limits) be allocated to groups which have 

 relatively easy requirements. 



TWO-WIRE SWITCHING — OTHER CONSIDERATIONS 



Present views are that even the ultimate plan will involve two-wire 

 switching at many points, mainly at the smaller switching points where 



2-W 



NC= NATIONAL CENTER 

 RC = REGIONAL CENTER 

 SC= SECTIONAL CENTER 

 P0= PRIMARY OUTLET 

 TO= TANDEM OUTLET 

 (SAME AS PO BUT WITH 

 SWITCHING equipment) 



TC= TOLL CENTER 

 [is] = ECHO SUPPRESSOR 

 (REQUIRED)* 



[ks] = ECHO SUPPRESSOR 

 (IF NECESSARY)* 



= FINAL GROUP 



= HIGH USAGE GROUP 



IF ECHO SUPPRESSOR IS USED, THE 

 ASSIGNED LOSS IS 0.5 DB UNLESS 

 A HIGHER VALUE IS REQUIRED FOR 

 CROSSTALK. 



TC"A" TC"B' 



Fig. 5 — Intertoll routing pattern between two regions showing typical circuit 

 groups. 



