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words, the tandem office T shown on Fig. 26 may consist of a group of 

 office selectors such as have been described previously. In this case 

 the trunks from offices M-l, M-2 and M-3 would lead from district 

 selectors in these offices to the office selectors at office T which would 

 select, under control of the sender in the originating office, an idle 

 trunk to office M-4, M-5, or M-6, as desired. At the terminating 

 office the call would be completed through incoming and finals if it is 

 a machine switching office, or call indicator "B" positions if it is a 

 manual office, exactly as described previously. 



If the number of points to be reached through the tandem office is 

 greater than the capacity of a group of office selectors, a group of 

 district selectors may be provided at the tandem office which have 

 access to groups of office selectors located at the same office or at 

 some distant point, as described above. 



Fig. 27 — Tandem Trunking Plan Showing Distant Office Selector 



Fig. 27 shows schematically a tandem plan using the above method. 

 Tandem office T is provided with district selectors on which terminate 

 trunks from local office M-l, M-2 and M-3. These selectors have 

 access to office selectors in the same office through which offices M-4 

 and M-5 are reached, and to office selectors located in the distant 

 tandem office T-l through which office M-6 and M-7 are reached. 



To handle calls at a machine switching tandem office originating 

 from manual offices, operators are required at the tandem office. 

 These operators handle calls in much the same manner as cordless 

 "B" operators in a machine switching office, as already described. 

 The operator receives the desired office name and number from the 

 originating operator over a call circuit and sets it up on her keyboard, 

 which is similar to the cordless " B " board, except that it has office keys 

 in addition to numerical keys. The number is received by a sender 

 which then controls the operation of the selecting mechanism in the 



