PRIVATE LINE DATA TRANSMISSION 1455 



Some comparison data are indicated for telephone speech. The bit 

 rate given assumes particularly message communication and not finer 

 shades of artistic expression. For this a collection of phonemes (or 

 elementary sounds) in the fifties, needing six bits for identification, and 

 a typical speech rate of eight phonemes per second, require 48 bits per 

 second. A few bits are also needed for pitch indication, and the figure 

 is rounded to 50. 



The low bit rate obtained for telephone speech communication indi- 

 cates considerable redundancy in the speech signal sent over the tele- 

 phone channel. This suggests why substantial transmission impairments 

 can be tolerated without destroying the intelligibility of speech, as 

 compared with telegraph or data signals. 



1.3 Nature of Study 



The procedure followed has consisted of examining systems of binary 

 or similar signal transmission which appeared suitable for the sending 

 of data. The systems studied are listed here, and some description of 

 them is given later in the text. As noted, part of the information has 

 come from outside the Bell System. 



1. Exploratory 1,650 bit per second vestigial sideband system studied 

 at Bell Telephone Laboratories. 



2. Exploratory 1,600 bit per second vestigial sideband system studied 

 at Lincoln Laboratory of M.LT.* 



3. Exploratory 750 bit per second double sideband system, of general 

 type reported by Horton and Vaughan.^ 



4. Voice frecjuency telegraph channels.^ 



5. "Polytonic" signaling system reported by Lovell, McGuigan and 

 Murphy.^ 



The transmission problem of applying these various systems to the 

 various tj^pes of telephone message facilities employed for private line 

 service has been considered. These are also listed, and a brief character- 

 ization of them is given in the text. 



1. ^^oice frequency circuits, over cable and open wire. 



2. Type-C carrier circuits for open wire.^^ 



3. Type-N carrier circuits for cable.® 



4. Broad-band carrier systems'^ using A channel banks for paired 

 cable, coaxial cable, open wire, and microwave radio. 



5. Other broad-band carrier systems. 



