34 



BELL SYSTEM TECHNICAL JOURNAL 



about 28 per cent. These figures show that in spite of the continued 

 increase in the number of telephones in service, the number of toll 

 messages per telephone have increased by about 30 per cent for this 

 period. 



One important cause of the rapid increase in toll usage has been 

 the material improvements in toll service. 



Figure 26 shows the increase in the speed of toll service since 1920 

 expressed in terms of the average time required from the placing of 

 a call to the response of the called party, or until the operator gives 



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Fig. 26 — -The average time required from tliL' placing of a toll call to the response of 

 the called party, or until a definite report is made by the operator. 



a definite report regarding the call. The service is sufficiently fast 

 so that on 95 per cent of the calls, the subscriber stays at the tele- 

 phone. This makes possible still more rapid service and simplified 

 operation. 



There have also been very great improvements during this period 

 in the clearness of speech transmission. The maximum permissible 

 transmission loss between two subscribers on a toll connection has 

 been materially reduced. The toll plant and subscriber plant are 

 now so designed that most of the messages are handled with a maxi- 

 mum transmission equivalent for the longest subscriber lines of 20 

 to 25 decibels overall referred to the standard transmission reference 

 system. 



