Transmission Aspects of Data Transmission 



Service Using Private Line Voice 



Telephone Channels 



By P. MERTZ and D. MITCHELL 



(Manuscript received February 2, 1957) 



An exploration is reported of the possibilities of a moderately fast data 

 transmission system to use private line message facilities. A comparatively 

 conventional system was desired to permit expeditious application. An 

 auxiliary ''word start" signal was necessary for the system considered. 



Transmission characteristics of a number of arrangements were examined. 

 These included several exploratory AM vestigial sideband systems {using a 

 spectrum similar to telephotography), double sideband AM systems, various 

 telegraph and other midtichannel systems. 



It was concluded that the 1600 bits per second usable over the AM vestigial 

 sideband arrangement was about as fast as could be expected with the data 

 system contemplated. This transmission is not as '^rugged," with respect to 

 impulse noise and sudden level changes, as other slower arrangements, but 

 it is expected to be satisfactory. It will require delay correction, and simple 

 methods are considered for carrying this out. 



I. INTRODUCTION 



The Bell System has been approached on a number of occasions in 

 regard to the transmission of computing machine and similar data over 

 its telephone circuits. This has reached the point where specific possibil- 

 ities for private line data transmission have been given serious consider- 

 ation. 



The telephone network was developed for speech transmission, and 

 its characteristics were designed to fit that objective. Hence, it is recog- 

 nized that the use of it for a distinctly different purpose, such as data 

 transmission, may impose compromises both in the mediinn and in the 

 special service contemplated. 



A short time ago the authors were assigned the problem of examining 

 possibilities for such an adaptation aimed at high speed, and exploring 



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