MACHINE SWITCHING TELEPHONE SYSTEM '?? 



shown in Fig. 1, to the very complex arrangements providing signaling, 



switching, and transmission facilities for as many as ten thousand 

 lines in a single board, of the type shown in Fig. 2. 



As the subscribers increased in number it was found that beyond 

 a certain point it was no longer practicable or economical to have all 

 of the subscribers' lines brought to one center. It was therefore, 

 necessary to have several centers, the number depending upon many 

 factors, the most important of which are the size and telephone needs 

 of the community. 



Fig. 2 — Modern Type Common Battery Switchboard 



The consequence of all this is that in large metropolitan areas the 

 number of centers is large, and the trunking system complex, as each 

 center must be provided either directly or indirectly with trunks to 

 every other center. 



As an illustration, take the New York Metropolitan area, shown in 

 Fig. 3, where the telephone plant is of the greatest intricacy because 

 of the very large number of subscribers served. There are at the 

 present time 158 central office switchboards, many of them having 



