Ethernet
Ethernet is a family of frame-based computer networking technologies for local area networks (LAN’s). The name comes from the physical concept of the ether. It defines a number of wiring and signaling standards for the physical layer, through means of network access at the Media Access Control (MAC)/Data Link Layer, and a common addressing format.
Ethernet over coaxial cable is not a new concept. Ethernet was originally developed at Xerox PARC in 1973–1975 and was based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium. From this early and comparatively simple concept, Ethernet evolved into the complex networking technology that today underlies most LAN’s. The coaxial cable was replaced with point-to-point links connected by hubs and/or switches to reduce installation costs, increase reliability, and enable point-to-point management and troubleshooting. StarLAN was the first step in the evolution of Ethernet from a coaxial cable bus to a hub-managed, twisted-pair network (10BASE-T). The advent of twisted-pair wiring dramatically lowered installation costs relative to competing technologies, including the older Ethernet technologies.
Despite the significant changes in Ethernet from a thick coaxial cable bus running at 10 Mbit/s to point-to-point links running at 1 Gbit/s , all generations of Ethernet (excluding early experimental versions) share the same frame formats (and hence the same interface for higher layers), and can be readily interconnected. Two significant generations in the development of Ethernet are discussed below.
10BASE5
10BASE5 (also known as thicknet) is the original "full spec" variant of Ethernet, using special cable similar to RG-8/U coaxial cable. This is a stiff, 0.375 inch (approx. 9.5 mm) diameter cable with an impedance of 50 ohms, a solid centre conductor, a foam insulating filler, a shielding braid, and an outer jacket.
The name 10BASE5 is derived from several characteristics of the physical medium. The 10 refers to its transmission speed of 10 Mbit/s. The BASE is short for baseband signalling as opposed to broadband, and the 5 stands for the maximum segment length of 500 metres (approx 1600 feet).
10BASE2
10BASE2 (also known as cheapernet, thin ethernet, thinnet or thinwire) is a variant of Ethernet that uses thin coaxial cable (RG-58 or similar, as opposed to the thicker RG-8 cable used in 10BASE5 networks), terminated with BNC connectors. For many years this was the dominant 10 Mbit/s Ethernet standard, but due to the immense demand for high speed networking, the low cost of Category 5 Ethernet cable, and the popularity of 802.11 wireless networks, both 10BASE2 and 10BASE5 have become almost obsolete.
10BASE2 systems do have a number of advantages over 10BASE-T. They do not need the 10BASE-T hub, so the hardware cost is very cheap, and wiring can be particularly easy since only a single wire run is needed.. These characteristics mean that 10BASE2 is ideal for a small network of two or three machines. For a larger complex office network the difficulties of tracing poor connections make it impractical.
The name 10BASE2 is derived from several characteristics of the physical medium. The 10 comes from the maximum transmission speed of 10 Mbit/s (millions of bits per second). The BASE stands for baseband signalling, and the 2 represents a rounded up shorthand for the maximum segment length of 185 meters (607 feet).
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