In the 20 years since Ethernet first arrived on the scene as a low-cost, high-bandwidth 10 Mbps LAN service for office automation applications, it has carved a niche for itself that transcends its original purpose. Today it is used in LANs, metropolitan area networks (MANs), and wide area networks (WANs) as both an access and transport technology. Its bandwidth capabil- ities have evolved to the point that the original 10 Mbps version seems almost embarrassing; a 10 Gbps version of the technology now exists.

Today s Ethernet product is based on the Institute of Electrical and Electronics Engineers (IEEE) 802.3 standard and its many variants, which specify the CSMA/CD access scheme (explained in a moment) and a handful of other details. It is perhaps important to note that Ethernet is a product name, originally invented and named by 3Com founder Bob Metcalfe. CSMA/CD is the more correct name for the technology that underlies Ethernet s functionality and the 802.3 standard. The term Ethernet, however, has become the de facto name for the technology.

Ethernet evolved in stages, all based upon the original IEEE 802.3 standard, which passed through various evolutionary phases of capability including 10 (Ethernet), 100 (Fast Ethernet), 1000 (Gigabit Ethernet), and 10,000 Mbps (10 Gbps Ethernet) versions. All are still in use, which allows for the design and implementation of tiered corporate Ethernet networks. A corporation, for example, could build a gigabit backbone, connected to Fast Ethernet access links, and connected in turn to...