MACHINE SWITCHING TELEPHONE SYSTEM 65 



the service conditions are extremely complex. It is, in effect, the 

 brains of the system, dealing with the subscriber and controlling the 

 selection until the destination is reached, as an operator deals with 

 the subscriber and controls the selection in a manual system. The 

 number dialed conveys the same information to the sender in a ma- 

 chine switching system as the number spoken by the subscriber does 

 to an operator in a manual system. 



The sender is an arrangement of relays, sequence switches, and 

 selectors, so worked out as to perform the following more important 

 functions: 



1. It receives a succession of electrical impulses from the subscrib- 

 er's dial which are on a decimal basis, stores them and translates 

 them to a non-decimal basis, corresponding to the particular group of 

 lines and trunks that is involved in the path of the call. 



2. It controls selecting mechanisms which build up the connection 

 to the called party in such a manner that each mechanism is given 

 the exact time required to perform its functions without any waste of 

 time, independently of the rate received from the dial. 



3. It makes the central office designations entirely independent of 

 the arrangement of the trunk groups on the selector frames. This 

 is a very important matter, inasmuch as it allows the selectors to be 

 used to full efficiency. It provides the desired flexibility for growth 

 and permits any desirable rearrangement of the trunks on the selector 

 frames that the telephone company may find desirable at any time. 



4. The sender is capable of distinguishing the class of office at 

 which the connection terminates. That is, if the call is to terminate 

 at a mechanical office, the sender will arrange to govern the selection 

 accordingly. If the call is to terminate at a manual office, the sender 

 recognizes this and arranges to send out impulses to the call indicator 

 equipment in the manual office. 



5. For the completion of certain calls, traffic conditions require the 

 introduction of tandem centers as discussed later. The sender 

 recognizes calls to be routed via tandem centers and arranges to 

 handle these correctly. The tandem center may be manual or it 

 may be mechanical, and the control must be determined accordingly. 



6. Certain senders are arranged to serve lines supplied with coin 

 boxes. These senders are arranged to make a test to determine 

 whether a coin has been deposited and do not allow the connection to 

 be cut through so that conversation can take place until the coin is 

 deposited. If the subscriber does not deposit the coin, after a reason- 

 able time has elapsed the sender connects an operator to the subscriber, 

 and this operator notifies the subscriber of his omission. After the 



