256 



THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1956 



CROSSBAR CROSSPOINT 



OR 



SWITCH CONTACTS 



-^ 



TO LINE 



-^ 



TO OTHER 



CENTRAL OFFICE 



EQUIPMENT 



9 9 



r 



^ 



LR 





■^f- 



CO 



c 



HI 



"H 



1_ 



(a) 



■:l 



LINE BUSY 



SERVICE 

 REQUEST 



I + 5V 



CROSSPOINT 



■^ 



TO LINE 



-^ 



TO 



CENTRAL 



OFFICE 



^4- 



-X 



-16V 



-16 VOLTS -NORMAL 

 (RECEIVER ON HOOK) 



-3 VOLTS -AWAITING SERVICE 

 (RECEIVER OFF HOOK) 



-16 VOLTS -CROSSPOINT CLOSED 

 (RECEIVER OFF HOOK) 



S\. 



-¥^ 



-16 V 



^ 



LINE BUSY 



+ 15 VOLT 

 TIME SLOT PULSE 

 FROM SCANNER 



GATE 



SERVICE 

 REQUEST 



Fig. 3 — (a) Relay line circuit, (b) Passive line circuit. 



