000 00287 a2200121 4500
082 _a621.382
_bOPE
090 _c13489
_d19853
245 _aDigital telecommunication
260 _bOpen university
_c1990
_g1990
300 _a14p.
_c29cm
650 _aCommunications engineering
942 _cL
999 _c41820
_d41820