National Extension College. <br/><br/>
Telephone switching systems II : section A : introducing signalling  [Books]. 
National Extension College. 
 - Cambridge  National Extension College  1980 
<br/><br/><label>ISBN: </label>0860825280  0.00 
<br/><br/><label>Subjects--Personal Names: </label><br/>Telephone -- Signalling.
<br/><br/><label>Dewey Class. No.: </label>TK/6392  / INT