000 00280 a2200121 4500
020 _a8176350664
082 _a004.6/.7 HEL
245 _aUnderstanding Data Communications
_cGilbert Held
250 _a5/e
260 _bTechmedia
_cc1996
300 _axx,504p
100 _aHeld Gilbert
999 _c1413
_d1413