TRANSLATORS AND IDENTIFIERS IN SWITCHING SYSTEMS 621 



single identifier has capacity to handle up to 50,000 numbers on a one- 

 at-a-time basis. 

 This identifier has not been developed beyond the laboratory stage.^° 



Passive Element Identifier 



Figure 13(a) shows a scheme for the identification of caUing numbers by 

 the use of an identifier containing passive element output coding devices 

 consisting of condensers and resistors. The general operation is simple. A 

 tone is applied, again through the trunk and the switching sleeve and the 

 normal equipment to directory number cross connection to the directory 

 number terminal. This- tone passes through the termination and coding 

 elements to the bus-bar system, the code for the associated number being 

 formed by a tone mark on one bus in each decimal output group. Common 

 detectors and discriminators detect these tones and register the identified 

 number on an associated electronic register. From the register it is trans- 

 ferred to the output system by suitable marks on the code marking leads. 



This identifier operates in about the same time as that of Fig. 12, that is, 

 less than 30 milliseconds, and is therefore also capable of serving 50,000 

 Unes without duplicating the translator equipment. This device is not in 

 use but is testing satisfactorily in the laboratory. So far it seems the most 

 economical of all the various types suitable for calling number identifica- 

 tion. 



Identifiers Arranged for Transmitting Identity Code to Input 



Figure 13, (b) and 13(c), shows two variations of identifiers operating on 

 the basis that the identification code formed by the coding elements is not 

 transmitted to a common output but back to the input end. 



Figure 13(b), used for calling number identification, uses non-linear coding 

 elements which are non-conductive normally. When a start voltage is ap- 

 plied to one of the coding elements from a trunk or a control element through 

 the switching stages on one of the switching conductors, the coding 

 element becomes conductive and connects the input end to the coding bus- 

 bar system which causes the identifying code to be sent back to the in- 

 quiring source. The identifying codes in this case are combinations of fre- 

 quencies or multipbx pulses. This device is in commercial operation. 



Figure 13(c) shows a similar arrangement used in the Bell System for 

 identifying frame numbers in a crossbar system. ^^ 



^° There is no published material on this identifier. A ratent has bfci allowed Mr. R. 

 P. Murphy of the B. T. L. An earlier version of this identifier is describe 1 in U. S. Patent 

 2,319,424 issued to Mr. M. E. Maloney of the B.T.L. 



^^ 0. Myers, "Multifrequency Frame Identification in Crossbar Toll," Bdl Labora- 

 tories Record, September 1944. 



