00331nam a22001217a 4500020001500000040000900015082001500024100001800039245005800057250001600115260004200131650003600173  a8178080982  cNUST  a004.6bHAL  aHalsall, Fred  aData Communication Computer Networks and Open Systems  a4th Edition  aSingapore:bPearson Education,c2002.  aComputer Communication Networks