Crossbar Dial Telephone Switching System

T T i s t h e p u r p o s e o f t h i s p a p e r t o describe briefly t h e c r o s s b a r dial t e l e p h o n e c e n t r a l office s w i t c h i n g s y s t e m w h i c h h a s r e c e n t l y been d e v e l o p e d b y t h e Bell S y s t e m for use i n large cities. Sixteen y e a r s ago, in F e b r u a r y 1923, a p a p e r w a s r e a d b e f o r e t h e I n s t i t u t e , by Messrs. E. B. Craft, L. F. Morehouse a n d H. P. Charlesworth of the Bell S y s t e m w h i c h o u t l i n e d t h e h i s t o r y a n d t h e p r o b l e m s i n v o l v e d i n t e l e p h o n e c e n t r a l office s w i t c h i n g a n d described t h e p a n e l dial c e n t r a l office s y s t e m which h a d j u s t been d e v e l o p e d a n d w a s b e i n g i n t r o d u c e d in t h e large cities. T h e first c e n t r a l office of t h i s t y p e w a s placed in service in D e c e m b e r 1921, a n d since t h a t t i m e 456 panel dial offices s e r v i n g n e a r l y f o u r a n d one-half million s u b s c r i b e r s t a t i o n s h a v e b e e n installed i n 2 6 d i f f e r e n t cities t h r o u g h o u t t h e c o u n t r y . During these y e a r s m a n y i m p r o v e m e n t s h a v e been m a d e i n t h e panel s y s t e m t o m a k e i t m o r e serviceable t o t h e t e l e p h o n e p u b l i c a n d t o m e e t t h e n e w * Presented at Winter Convention of A.I.E.E., New York, N. Y., January 23-27, 1939. 76