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Chapter 6. Ethernet

Chapter 6. Ethernet

Ethernet will play a very important role in home networking. It can be directly installed within a room with a bunch of twisted pair patch cables or in a house with home run wired Category 5 twisted pair cables. Furthermore, other existing wiring–based home networking systems are also based on the Ethernet frame format and the Media Access and Control protocol. Operation principles of wireless Ethernet and its home networking variations are very close to that of the original Ethernet. The concept of Ethernet was originated by Bob Metcalfe and his Xerox PARC colleagues in late 1972 to interconnect personal workstations. Their first experimental network was called the Alto Aloha Network. In 1973, Metcalfe changed the name to Ethernet, to make it clear that the system could support any computer and to point out that his new network mechanisms had evolved well beyond the Aloha system. He chose to base the name on the word “ether” as a way of describing an essential feature of the system: the physical medium (i.e., a cable) carries bits to all stations, much the same way that the old luminiferous ether was once thought to propagate electromagnetic waves through space.

After some refinement, the second generation called Ethernet II was widely used. Ethernet from this period is often called DIX after its corporate sponsors Digital, Intel, and Xerox. As the holder of the trademark, Xerox established and published the original standards for a coaxial cable–based Ethernet in 1980. The Institute of Electrical and Electronics Engineers (IEEE) was assigned the task of developing formal international standards for all Local Area Network technology. It formed the “802” committee to look at Ethernet, Token Ring, Fiber Optic, and other LAN technology. The thick coaxial media system was the first media system specified in the IEEE Ethernet, CSMA/CD, standard of 1985. The thick coaxial cable–based Ethernet is also called 10Base5 and can carry a transmission data rate of 10 Mbps. 10Base5 uses relatively inflexible coaxial cable with a diameter of 1 centimeter. A thin coaxial cable version of Ethernet, named 10Base2, was subsequently developed in 1987. The diameter of a thin coaxial cable is 0.5 centimeter (cm). This thin coaxial cable is also known as RG-58 and has an impedance of 50 ohms. In comparison, coaxial TV cables are either RG-6 or RG-59 and have an impedance of 75 ohms.


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