Smith, S.F.
Telephony and telegraphy : an introduction to instruments and exchanges - 2d ed. - London O.U.P. 1974 - 282 p.
621.39 / S6
Telephony and telegraphy : an introduction to instruments and exchanges - 2d ed. - London O.U.P. 1974 - 282 p.
621.39 / S6