Ethernet operates at layer two of the OSI reference model. Layer two, also known as the Data Link Layer, is subdivided into the Logical Link Control (LLC) layer and the Media Access Control (MAC) layer. Ethernet nodes use a globally-unique 48-bit address called the MAC address to communicate within a network. Datagrams at layer two are called frames. The frame structure used by modern Ethernet is the same as that used by earlier coaxial-cabled Ethernet networks, thus providing a level of backwards compatibility. Ethernet is a family of frame-based computer networking technologies for local area networks (LANs). The name comes from the physical concept of the ether. It defines a number of wiring and signaling standards for the Physical Layer of the OSI networking model, through means of network access at the Media Access Control (MAC) /Data Link Layer, and a common addressing format.

                    While the early coaxial cable based variants of Ethernet were half-duplex by design, all the common variants of twisted pair (10BASE-T, 100BASE-TX and 1000BASE-T) and fiber optic Ethernet provide separate channels for send and receive.

To allow use of hubs and for compatibility with existing variants of Ethernet they were initially implemented in a half-duplex manner with the transceiver (usually by this point integrated into the device) detecting a collision if an attempt was made to transmit and receive simultaneously and looping back data to the host so it could hear itself transmit (as it would on a shared medium).

However if both ends of the link are not hubs, and the hardware supports it, the two channels can be split and used to make a full-duplex link. Unfortunately if autonegotiation is enabled on one end and forced full-duplex on the other, the end with autonegotiation will detect the link as half-duplex causing large numbers of errors due to duplex mismatch.

 10Gbit Ethernet is also called 10GigE. This was first published in 2002 and is still the fastest Ethernet standard, although 100Gbit Ethernet is under development. The standard includes 10GBase-SR, 10GBase-LR, 10GBase-LRM, 10GBase-ER, 10GBase-ZR and 10GBase-LX.

For more details, cLiCk hErE