Helmers, Scott A <br/><br/>
Data communications : a beginner's guide to concepts and technology 
by Scott A Helmers 
 - New Jersey  Prentice hall  1989 
 - xvii, 302p. 
<br/><br/><label>ISBN: </label>0131988700 
<br/><br/><label>Dewey Class. No.: </label>621.3981  / N89