PDF of this tutorialEthernet was defined as an open standard in the early 1980s by a consortium comprised of Digital Equipment Corp., Intel, and XEROX; the resulting standard was called the DIX Ethernet Spec. The goal was to promote a relatively high-performance and low-cost LAN implementation using digital (baseband) signaling on a shared coaxial cable.
In 1983, the IEEE 802 Local-Area Network/Metropolitan-Area Network Standards Committee (LMSC) released the 802.3 standard for Ethernet—a shared medium for LANs using a distributed media access control (MAC) mechanism called carrier sense multiple access with collision detection (CSMA/CD).
Ethernet has proven to be a highly flexible standard. It has evolved to include point-to-point signaling, full-duplex (unshared) links, and very-high-speed networks. Several Ethernet characteristics have persisted, the most important of these being the framing format itself (see Figure 1). An Ethernet frame specifies a minimum and maximum packet size, a “protocol-type” field (expanded by 802.3 to function sometimes as a packet-length field), and both a destination and a source MAC address. The address fields have been particularly valuable, as the globally unique MAC addresses (each 48 bits long) have enabled the creation of new devices (Ethernet switches) that have simplified the development of large Ethernet networks.
Optical links have been a part of Ethernet standards since the early 1980s. The needs and potential of optical transport, including point-to-point and full-duplex links, have driven some of the evolution of Ethernet. Optical Ethernet technologies are providing the longest spans and greatest speeds used in LANs today, and they will undoubtedly, continue to do so in the future.
Figure 1. Ethernet Frame
