With the release of 802.3x, full-duplex Ethernet arrived on the scene, a protocol that operates effectively without the benefit of CSMA/CD. Full-duplex transmission enables stations to simultaneously transmit and receive data over a single point-to-point link. As a result, the overall throughput of the link is doubled.

For full duplex to operate on an Ethernet LAN, facilities must meet following stringent requirements:

• The medium itself must support simultaneous two-way transmission without interference. Media that meet this requirement include 10BaseT, 10BaseFL, 100BaseTX, 100BaseFX, 100BaseT2, 1000BaseCX, 1000BaseSX, 1000BaseLS, and 1000BaseT. 10Base5, 10Base2, 10BaseFP, 10BaseFB, and 100BaseT4 are incapable of supporting full-duplex transmission.

• Full-duplex operation is restricted to point-to-point connections between two stations. Because no contention exists (only two stations are available, after all), collisions cannot occur and CSMA/CD is not required. Frames can be transmitted at any time, limited only by the minimum interframe gap.

• Both stations must be configured for full-duplex transmission.

Needless to say, full-duplex operation results in a far more efficient network since no collisions take place and therefore no bandwidth is wasted.