A channel unit network having a two-wire port for interconnecting a two-wire, bidirectional signal transmitting means with a four-wire digital transmitting means in a communication system to create a precision bidirectional simulated two-wire cable pair with an extended operation range over a transmission...http://www.google.fr/patents/US5586181?utm_source=gb-gplus-shareBrevet US5586181 - Metallic channel unit network
