10BASE2

10BASE2 (also known as cheapernet, thin Ethernet, thinnet, and thinwire) is a variant of Ethernet that uses thin coaxial cable, terminated with BNC connectors. During the mid to late 1980s 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 increasingly obsolete, though they still exist in some locations. As of 2011, IEEE 802.3 has deprecated this standard for new installations.

The name 10BASE2 is derived from several characteristics of the physical medium. The 10 comes from the transmission speed of 10 Mbit/s (millions of bits per second). The BASE stands for baseband signalling, and the 2 for a maximum segment length approaching 200 m (the actual maximum length is 185 m).

10 Mbit/s Ethernet uses Manchester coding. A binary zero is indicated by a low to high transition in the middle of the bit period and a binary one is indicated by a high to low transition in the middle of the bit period. This allows the clock to be recovered from the signal. However, the additional transitions double the signal bandwidth.

10BASE2 coax cables have a maximum length of 185 metres (607 ft). The maximum practical number of nodes that can be connected to a 10BASE2 segment is limited to 30 with a minimum distance of 50 cm. In a 10BASE2 network, each stretch of cable is connected to the transceiver (which is usually built into the network adaptor) using a BNC T-connector, with one stretch connected to each female connector of the T. The T-connector must be plugged directly into the network adaptor with no cable in between.

As is the case with most other high-speed buses, Ethernet segments have to be terminated with a resistor at each end. Each end of the cable has a 50 ohm (Ω) resistor attached. Typically this resistor is built into a male BNC and attached to the last device on the bus. This is most commonly connected directly to the T-connector on a workstation though it does not technically have to be. A few devices such as Digital's DEMPR and DESPR have a built-in terminator and so can only be used at one physical end of the cable run. If termination is missing, or if there is a break in the cable, the AC signal on the bus is reflected, rather than dissipated, when it reaches the end. This reflected signal is indistinguishable from a collision, so no communication can take place.

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