00614nam a2200193Ia 450000500170000000800410001702000150005804000180007304100080009108200210009910000190012024500580013925000120019726000440020930000270025365000390028065000390031965000620035820230706110527.0210716s2003    xx            000 0 und d  a8129702118  cAIMIT LIBRARY  aeng  a004.65 27bHELG  aHeld, Gilbert.  aUnderstanding data communications /cBy Gilbert Held.  a7th ed.  aNew Delhi :bPearson Education ,c2003.  axv,765p. ;bPBc24 cm.  aMessages and transmission channels  aAsynchronous modems and interfaces  aSynchronous modems digital transmission and service units