An apparatus for selectively granting priority use of telephone lines to a telephone or data transmitter each connected via the telephone lines to an exchange center. Access of the data transmitted to the exchange center is typically enabled by application of DC voltage of a predetermined polarity to...http://www.google.fr/patents/US4321429?utm_source=gb-gplus-shareBrevet US4321429 - Apparatus for selecting terminal equipment in telephone lines
Apparatus for selecting terminal equipment in telephone lines
