TRANSLATORS AND IDENTIFIERS IN SWITCHING SYSTEMS 623 



Here all the trunks in the same frame have one lead permanently con- 

 nected to a coding element which produces a 3-frequency code. This lead 

 is connected to common detection equipment when the frame identification 

 is wanted and this registers the frequencies and converts them to an out- 

 put on a code marking lead system. 



Identification by Reading Positions of Normal Selectors 



There are numerous patents and a few commercial systems involving 

 identification of calling subscribers, calHng trunks, selected trunks, selected 

 senders or registers, etc., in which the identification process consists in read- 

 ing the position of the fine finder, switch or relay unit which has been op- 

 erated to select the line, trunk or other unit involved. 



One of the oldest patents on calling number identification involves this 

 principle.^2 The number of the switch group plus the number of the switch 

 setting may in certain cases correspond directly to the wanted code. In 

 other cases this indication must be translated, sometimes to a new arbitrary 

 code and sometimes to obtain a code in a different numeration or signaling 

 system. 



Two methods of reading the switch positions are used: (1) counting of 

 the steps or checking and registering other action taken by the switch 

 during the time the involved fine or other circuit is being selected, and (2) 

 checking and registering the switch position after selection. 



One of the interesting applications of this method for calUng number 

 identification where the fine finder group and position numbers indicate the 

 calling number is illustrated in the article covered by footnote No. 2}^ 



Comments on Identifiers 



The identifiers we have discussed are divided into the following general 

 types: 



(1) Searching types 



(2) Coding element types 



Type A — with transmission to common output 

 Type B — With transmission to source over input lead 



(3) Switch position reading types 



The first two types depend on the use of a considerable amount of equip- 

 ment comprising the identifier and a large number of leads, and the prob- 

 lem of economy is generally solved by using one of the regular conductors 

 of each connection (usually the sleeve) as part of the identification circuit. 



12 Mr. W. W. Carpenter et al, U. S. Pat. 2,112,951. 



1^ R. F, Stehlik, "La Louviere Automatic Network of the Belgian Telephone Sys- 

 tem," The Automatic Electric Company Technical Journal, January 1951. 



