ELECTRONICS IX TELEPHONE SWITCHING SYSTEMS 



lOlo 



computers; however, in designing a telephone system an entirely dif- 

 ferent philosophy must be pursued since it should not be necessary to 

 have engineering caliber maintenance forces. At no time should the 

 system be incapable of accepting and completing calls. This does not 

 mean that portions of the system may not be worked on for routine or 

 trouble maintenance. 



A promising approach appears to be the use of marginal condition 

 routine tests for detecting in advance components which are about to 

 fail.^^ Automatic trouble locating arrangements may be devised for 

 giving information as to the specific location of a package in trouble 

 when it occurs.^^ This automatic trouble locator combined with the 

 equipment concept of plug-in units means that service may be main- 

 tained without long interruptions. By designing devices which are 

 reliable, employing them in a manner to give maximum service life and 



WITH DIODES 



WITH TRANSISTORS 



Fig. 26 — A logic function with diodes or transistors. 



