Held, Gilbert. <br/><br/>
Understanding data communications / 
By Gilbert Held. 
 - 7th ed. 
 - New Delhi :  Pearson Education ,  2003. 
 - xv,765p. ;  PB  24 cm. 
<br/><br/><label>ISBN: </label>8129702118 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Messages and transmission channels<br/>Asynchronous modems and interfaces<br/>Synchronous modems digital transmission and service units
<br/><br/><label>Dewey Class. No.: </label>004.65   / HELG