four wire cable (4W)

The four-wire line is a connecting line in the telephone connection. It consists of two twisted pairs, one each for the incoming and outgoing signal.

By twisting the cores in pairs or stranding the pairs of cores, the twin wires are less susceptible to interference.

Full duplex transmission is possible via the four-wire line, which was previously used in analog leased lines and private branch exchanges, but is still used today in cabling technology and in ISDN connections.