Ethernet 802.3X Full Duplex Protocol

The Ethernet 802.3X full duplex protocol is a subset of the IEEE 802.3 collection of standards that define the physical and data link layers of 10Base5 to 1000BASE5 wired Ethernet. It was defined in 1997, or exactly two years after the introduction of the 100Base-T standard, which is more commonly known as "Fast Ethernet," as it supports data transfer speeds of 100 MB/s

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Ethernet Origins

• Ethernet is a local area network, or LAN, technology originally developed at the Xerox Palo Alto Research Center during the 1970s. The Institute of Electrical and Electronic Engineers, or IEEE, standardized Ethernet in 1983 with the release of the 802.3 Working Group. Ethernet didn't become mainstream until 1985, when the IEEE 802.3a standard for "thin" 10Base2 was introduced, allowing 10 Mb/s connectivity over a broadband cable system.

Road to 802.3x

• Following the 1985 introduction of 10Base2 Ethernet, the speed of Ethernet developments quickly increased. In 1990, Ethernet over unshielded twisted pair, or UDP, cable was introduced. In 1993, the 802.3j standard for long-distance fiber optic connections was introduced. In 1995, the 802.3u standard for 100 MB/s Ethernet was introduced. In 1997, the 802.3x standard for full-duplex and flow-control 100 Mb/s Ethernet over UTP cable was introduced.

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802.3x Details

• The 802.3 full duplex protocol allows two servers to communicate simultaneously, increasing the data transfer rate, as one server can receive data even as it transmits it. If both servers are transmitting at 10 MB/s, then the total transmission speed is 20 MB/s. The protocol also adds flow control, a mechanism that modulates data transfers with a PAUSE frame. This halts transmissions until the slower server catches up to the faster server.

Upgrades

• Additional standards have been released since 1995. These include the 802.3y standard for 100 Mb/s transmission over two pairs of UTP, the 802.3z standard for Gigabit Ethernet and the 802.3ac standard for virtual LAN tagging on Ethernet networks. The 802.3x still is still available for use, but numerous administrators opt to not use it because flow control stops traffic, and often delays the transmission of data.