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BELL SYSTEM TECHNICAL JOURNAL 



equipment at the tandem office to reproduce over the trunk by means 

 of a talking film the digits of the number previously set up by the 

 originating or tandem operator. 



Trunks may also be provided from panel sender tandem offices to 

 local central offices having step-by-step equipment, to manual tandems, 

 and to dial tandems of either the panel or step-by-step type. 



TANDEM DISTRICT 



SELECTOR 



FRAME 



OFFICE 



SELECTOR 



FRAME 



STRAIGHT- 

 FORWARD 



INCOMING 

 TRUNKS 



OPERATOR TANDEM 

 LINK FRAME 



SENDER 

 SELECTOR 



FULL 

 SELECTOR TANDEM 

 LINK FRAME 



DISTRICT 

 FINDER 



SENDER 

 SELECTOR 



DISTRICT 

 FINDER 



TANDEM 

 POSITION FINDER 



TANDEM COMPLETING TRUNKS TO: 



I- INCOMING SELECTORS IN PANEL 

 AND STEP-BY- STEP DIAL OFFICES. 



2- CALL ANNOUNCER OR CALL IN- 

 DICATOR "B" POSITIONS IN 

 MANUAL OFFICES. 



3- PANEL OR STEP-BY- STEP 

 SUB- TANDEMS. 



4-CALL INDICATOR SUB-TANDEMS 



-NOTES- 



1- DIRECT TRUNKS MAY BE PRO- 

 VIDED FROM THE TANDEM 

 DISTRICT FRAMES TO THE 

 TERMINATING OFFICE , IF SPACE 

 ON THESE FRAMES IS NOT ALL 

 REQUIRED FOR TRUNKS TO THE 

 TANDEM OFFICE SELECTOR 

 FRAMES. 



2- INCOMING AND OUTGOING TAN- 

 DEM TRUNKS ARE ONE-WAY 

 ONLY. 



SENDER FRAME 



CALL 



ANNOUNCER 



MACHINE 



■ DECODERS 



OPERATOR 

 TANDEM POSITION 



SEMI -MECHANICAL 

 TYPE KEYSET 



Fig. 6 — Panel sender tandem system. 



Figure 6 shows schematically the latest type of panel sender tandem 

 system. Figure 7 is a photograph of the operators' positions at Sub- 

 urban Tandem, one of the panel tandem systems in New York City, 

 while Fig. 8 shows the area served by this system. 



An early type of panel sender tandem system known as the semi- 

 mechanical system is in use in New York City. It consists both of an 

 operator tandem and a full selector tandem. The former has opera- 



