| Ethernet was born of internal research
conducted at Xerox's famed Palo Alto Research Center in the early
1970s, following pioneering work of Norman Abramson at the
University of Hawaii on the ALOHANET project (using packet radio
between the islands in the late 1960s). Rather than being some bold
and innovative new technology that researchers strove to bring to
market, the origins of Ethernet are quite pedestrian. The
researchers needed a way to share their expensive laser printer
among their desktop workstations. The answer: a crude and somewhat
chaotic data link layer protocol that relied on higher-layer
protocols to behave properly. Somewhat tongue-in-cheek, these
researchers named their new pet Ethernet, a subtle play on words,
referring to the 'ether' used by physicists in the 1800s to describe
the underlying structure of space (later proved to be scientifically
unsound). From this humble beginning spawned a tremendous family of
related products, protocols, and technologies.
Today, many different varieties of
Ethernet exist. This family includes at least five different frame
formats, three different media access arbitration techniques, and an
ever-growing collection of medium-dependent interfaces (MDIs). The
MDI is the most visible aspect of the 802.3 physical layer; it
defines the expected type of transmission medium, as well as its
transmission and impedance characteristics. For the LAN to operate
properly, the correct transmission media must be connected to the
corresponding NIC, which contains the MDI logic.
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