TELEPHONE SYSTEM OF THE UNITED STATES 



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there are 36 million telephone connections handled each day by about 

 128,000 private branch attendants. About 17 per cent of all local 

 calls originate at these boards. Equipment of both the manual and 

 dial type is installed, the latter being particularly adapted to extension- 

 to-extension calling. Further data regarding private branch exchanges 

 are given in Fig. 5. 



The smallest manual installation is the cordless board illustrated 

 in Fig. 6 where connections are established by means of keys, and the 

 capacity is limited to three trunks and seven stations. A larger type, 



Fig. 6 — -Cordless private branch exchange installation for 7 stations and 3 central 



office trunks. 



using cords for the completion of connections, is illustrated in Fig. 7 

 with a capacity for fifteen trunks and 200 stations. 



For the largest private branch exchanges the equipment is of much 

 the same type as that used at central offices. A large switchboard 

 for one of the public utilities having 1,600 stations is shown in Fig. 8. 

 Connecting this private branch exchange with the central office there 

 are 148 lines and in addition 151 tie trunk lines extend to other private 

 branch exchanges having a business association. There are a total 

 of 42 switchboard positions. 



