618 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1951 



Calling Number Identifiers — Searching Type 



Figure 11 shows an identifier used in the Bell System's first appUcation 

 of automatic ticketing^ and with variations in similar applications else- 

 where. 



The principle here is that the identifier, through the outgoing trunk to 

 which the calling fine has been extended, applies a tone to the sleeve ter- 

 minal of the calling line, utilizing the sleeve through all the switching stages. 

 This tone finds its way through an equipment-to-directory number trans- 

 lating jumper to one terminal common for each 1000 numbers, one com- 

 mon for each 100 and one per number in each one hundred block. The 

 numbers of the terminals with tones correspond to the various decimal 

 digits of the caUing numbers. 



Relays connect tone detection equipment sequentially to the various 

 thousands, hundreds, etc. terminals and each time the tone is found the 

 corresponding digit is registered on relays in the identifier. These relays 

 mark the output code leads. 



The variations in other identifiers of the searching type consist of the 

 use of switches or tubes instead of relays, searching for special d-c. voltages 

 instead of tone, and in transmitting the digits of the identified number back 

 to the source of the identifying signal by pulses over the sleeve instead of 

 transmitting them to code marking output leads. 



This type of identifier is obviously rather slow because of the sequence 

 of operations and it is, therefore, necessary to provide a plurality of identi- 

 fiers for each office. The different identifiers are prevented from interfering 

 with each other by preference lock-out circuits, by discriminating signals 

 such as different tones or by other special means. 



A ll-Eleclronic Calling Number Identifier 



This proposed identifier works much like a translator in that a coding 

 element individual to each number is selected and this places marks on a 

 decimal bus-bar output system. Referring to Fig. 12, it will be noted that 

 there is a directory number field with a multi-anode tube of the type used 

 in Fig. 8 for each number plus an RC filter to discriminate against surges. 

 This identifier provides for party lines and for class of service indication 

 requiring the two extra cross connections shown. 



The operation consists in the application by the control unit through the 

 trunk and the switch sleeves to the line equipment sleeve terminal of a 10- 

 millisecond pulse of +135 volts. This finds its way through the normal 



' O. A. Friend, "Automatic Ticketing of Telephone Calls," Electrical Engineering, 

 Vol. 63, Transactions, pp. 81-88, March 1944. 



