Common Control Telephone Switching Systems

I n v e n t i o n of machines for switching telephone connections started s h o r t l y a f t e r t h e i n v e n t i o n of t h e t e l e p h o n e . A f o r e r u n n e r of t h e s t e p - b y step system, the Connolly and M c T i g h e "girlless" telephone system,* w a s p a t e n t e d i n 1879 a n d t h e f i r s t p a t e n t o n t h e S t r o w g e r s t e p - b y - s t e p s y s t e m f w a s issued in 1891. T h e first c o m m e r c i a l i n s t a l l a t i o n of a u t o m a t i c s w i t c h i n g e q u i p m e n t w a s m a d e a t L a P o r t e , I n d i a n a , i n 1892. T h i s installation used step-by-step mechanisms. I n t h e e a r l y 1900's m a n y t e l e p h o n e e n g i n e e r s r e g a r d e d f u l l a u t o m a t i c s w i t c h i n g a s u n e c o n o m i c a l b u t t e c h n i c a l l y f e a s i b l e i f r e s t r i c t e d t o single office e x c h a n g e s w i t h i n d i v i d u a l flat r a t e lines. T h e y were, h o w e v e r , u n * U. S. Patent 222,458--1879--Connolly and McTighe. t U. S. Patent 447,918--1891-- Almon B. Strowger. 1086 COMMON CONTROL S W I T C H I N G SYSTEMS 1087 certain about the f u t u r e of this method of operation. It appeared to t h e m t h a t t h e greatest promise in t h e use of a u t o m a t i c a p p a r a t u s was i n d i s t r i b u t i n g calls t o m a n u a l " A " o p e r a t o r s a n d i n t h e e l i m i n a t i o n o f t h e " B " operators. Consideration was being given to systems capable of o p e r a t i n g on e i t h e r a s e m i - m e c h a n i c a l or a f u l l m e c h a n i c a l b a s i s d e p e n d ing o n w h e t h e r t h e dial w a s l o c a t e d a t t h e " A " b o a r d o r a t t h e s u b s c r i b e r ' s s t a t i o n .