A full-duplex (FDX), accepts communication in both ways, and, unlike half-duplex, accept this to occur simultaneously. Land-line telephone networks are full-duplex, since they accept both callers be heard and to speak at the same time. A good principal for a full-duplex system would be a two-lane road with one lane for each way. Two-way radios may be, for instance, described as full-duplex systems, which receive a one frequency and transmit on a different frequency. This is also known frequency-division duplex. Frequency-division duplex machines can be extended to farther distances needing pairs of simple repeater bases, because the communications transferred on any one frequency always travel in the similar direction.