000 002870000a22001210004500
245 _aSignalling telecommunications net works
100 _aWelch, S.
260 _aLondon
_bIEE
_c1967
440 _aIEE telecommunication series
080 _a721.391
_bW4
041 _aEN
942 _cBK
999 _c113549
_d113549