10BASE5 (also known as thick Ethernet or thicknet) was the first commercially-available variant of Ethernet. 10BASE5 uses a thick and rigid coaxial cable up to 500 metres (1,600 ft) in length. Up to 100 stations were connected to the cable using vampire taps and shared a single collision domain with 10 Mbit/s of bandwidth shared among them. The system was difficult to install and maintain.
10BASE5 was superseded by much cheaper and more convenient alternatives: first by 10BASE2 based on a thinner coaxial cable, and then once Ethernet over twisted pair was developed, by 10BASE-T and its successors 100BASE-TX and 1000BASE-T.
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 (1,600 ft).
For its physical layer it used cable similar to RG-8/U coaxial cable but with extra braided shielding. This is a stiff, 0.375-inch (9.5 mm) diameter cable with an impedance of 50 ohms, a solid center conductor, a foam insulating filler, a shielding braid, and an outer jacket. The outer jacket was often yellow-to-orange foam fluorinated ethylene propylene (for fire resistance) so it often is called "yellow cable", "orange hose", or sometimes humorously "frozen yellow garden hose". 10BASE5 coaxial cables had a maximum length of 500 metres (1,600 ft). Up to 100 nodes could be connected to a 10BASE5 segment.
Transceiver nodes could be connected to cable segments with N connectors, or via a vampire tap, which allowed new nodes to be added while existing connections were live. A vampire tap clamped onto the cable, forcing a spike to pierce through the outer shielding to contact the inner conductor while other spikes bit into the outer braided shield. Care was required to keep the outer shield from touching the spike; installation kits included a "coring tool" to drill through the outer layers and a "braid pick" to clear stray pieces of the outer shield.
Transceivers could be installed only at precise 2.5-metre intervals. This distance was chosen to not correspond to the wavelength of the signal; this ensured that the reflections from multiple taps were not in phase. These suitable points were marked on the cable with black bands. The cable was required to be one continuous run; T-connections were not allowed.
As is the case with most other high-speed buses, segments must be terminated at each end. For coaxial-cable-based Ethernet, each end of the cable had a 50 ohm resistor attached. Typically this resistor was built into a male N connector and attached to the end of the cable just past the last device. With termination missing, or if there was a break in the cable, the signal on the bus would be reflected, rather than dissipated when it reached the end. This reflected signal is indistinguishable from a collision, and so no communication was possible.
Adding new stations to network was complicated by the need to accurately pierce the cable. The cable was stiff and difficult to bend around corners. One improper connection could take down the whole network and finding the source of the trouble was difficult.
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