00266nam a2200109Ia 4500008004000000082001700040100001600057245002900073260002900102300001100131650001400142210210b1980   xxu||||| |||| 00| 0 eng d  a621.385 JAIP  aJAIN (A K).  aPrinciples of telephony.  aDelhibNew heightsc1980  aiv,260  aTelephony