LONG DISTANCE TELEPHONE CIRCUITS 



535 



subscriber to a regional center. As there are eight regional centers 

 in the United States and 29 national networks which constitute the 

 European continental network, the areas involved in the comparison 

 are not wholly comparable. 



The application of these transmission requirements leads to the 

 following approximate limits for the use of the different standard 

 types of toll cable construction in the toll circuits of the United States: 



19-gauge B and H-88-50 two-wire circuits 

 19-gauge B and H-88-50 two-wire circuits 



19-gauge H-44-25 four- wire circuits with- 

 out echo suppressors 



19-gauge H-i4-25 four-wire circuits with- 

 out echo suppressors 



250 miles (400 kilometers) when used 



exclusively for terminating business 

 135 miles (220 kilometers) for circuits 



used for switched business 

 650 miles (1050 kilometers) when used 



exclusively for terminating business 

 270 miles (430 kilometers) for circuits 



used for switched business 



Use of Toll Cables in the United States 

 In the application of toll cables to meet the service requirements of 

 the United States use is generally made of cables 2^ inches (67 

 millimeters) in outside diameter, although to some extent use has been 

 made of cables 33^8 inches (79 millimeters) in outside diameter. A 

 large proportion of the new toll cables contain one of the combinations 

 of gauges indicated in the following table: 



TABLE III 



The present toll cable routes in the United States are indicated on 

 the map shown in Fig. 5, together with probable future extensions. 

 The existing network includes 13,000 miles (21,000 kilometers) of 

 route, 21,000 miles (34,000 kilometers) of cable, and when fully 

 equipped, 5,000,000 miles (8,000,000 kilometers) of circuit. 



The division of the cable between various types of construction is 

 indicated in the following table: 



Underground in ducts 46% 



Aerial 50% 



Buried underground 4% 



As an illustration of the practical application of toll cable, some 

 information is given below regarding the makeup of some of the 

 circuits out of New York City. There are associated with the New 

 York toll board 235 groups of circuits. In order to avoid too cumber- 



