View source for 10BASE2

{{Short description|Once-dominant 10 Mbit/s Ethernet standard}}
{{refimprove|date=January 2016}}

[[File:BNC connector with 10BASE2 cable-92170.jpg|thumb|10BASE2 cable showing the BNC connector end.]]
[[File:BNC Tee connector, with Ethernet cable connected-92166.jpg|thumb|10BASE2 cable with a BNC T-connector.]]
[[Image:10base2 BNC Terminator.jpg|thumb|right|10BASE2 cable end terminator.]]
[[Image:Ead-outlet.jpg|thumb|right|EAD outlet]]
[[Image:AAUI examples.jpg|thumb|right|Different types of T-connectors, with [[AAUI]]s (an AUI variant specific to [[Apple Inc.|Apple]] computers)]]

'''10BASE2''' (also known as '''cheapernet''',<ref>{{cite web |url=http://bitsavers.trailing-edge.com/components/national/_appNotes/AN-0442.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://bitsavers.trailing-edge.com/components/national/_appNotes/AN-0442.pdf |archive-date=2022-10-09 |url-status=live |title=Ethernet/Cheapernet Physical Layer Made Easy with DP8391/92 |author=Alex Djenguerian |date=June 1986 |publisher=National Semiconductor |access-date=2019-08-13}}</ref> '''thin Ethernet''', '''thinnet''', and '''thinwire''') is a variant of [[Ethernet]] that uses thin [[coaxial cable]] terminated with [[BNC connector]]s to build a [[local area network]]. During the mid to late 1980s, this was the dominant {{val|10|ul=Mbit/s}} Ethernet standard.

The use of [[twisted pair]] networks competed with 10BASE2's use of a single coaxial cable. In 1988, [[Ethernet over twisted pair]] was introduced, running at the same speed of 10&nbsp;Mbit/s. In 1995, the [[Fast Ethernet]] standard upgraded the speed to 100&nbsp;Mbit/s, and no such speed improvement was ever made for thinnet. By 2001, prices for Fast Ethernet cards had fallen to under $50. By 2003, [[Wi-Fi]] networking equipment was widely available and affordable.

Due to the immense demand for high-speed networking, the low cost of [[Category 5 cable]], and the popularity of [[802.11]] wireless networks, both 10BASE2 and [[10BASE5]] have become increasingly [[obsolete]], though devices still exist in some locations.<ref>{{cite news |url=http://www.l-com.com/content/Article.aspx?Type=P&ID=10042 |title=L-com Introduces Commercial-Grade Thinnet (10Base-2) and Thicknet (10Base-5) Converters for Legacy Installs |date=2012-06-11 |publisher=L-com, Inc. |access-date=2012-07-01}}</ref> As of 2011, [[IEEE 802.3]] has [[deprecated]] this standard for new installations.<ref>IEEE 802.3-2012 ''10. Medium attachment unit and baseband medium specifications, type 10BASE2''</ref>

==Name origination==
The name ''10BASE2'' is derived from several characteristics of the physical medium. The ''10'' comes from the transmission speed of 10&nbsp;[[Mbit/s]]. The ''BASE'' stands for [[baseband]] signaling, and the ''2'' for a maximum segment length approaching 200&nbsp;m (the actual maximum length is 185&nbsp;m).

==Signal encoding==
10&nbsp;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. Manchester coding allows the clock to be recovered from the signal. However, the additional transitions associated with it double the signal bandwidth.

==Network design==
10BASE2 coax cables have a maximum length of {{convert|185|m|ft}}. The maximum practical number of nodes that can be connected to a 10BASE2 segment is limited to 30<ref>IEEE 802.3 ''10.7.2.2 MAU placement''</ref> with a minimum distance of {{convert|0.5|m|in}} between devices.<ref>IEEE 802.3 ''10.7.2.1 Cable sectioning''</ref> In a 10BASE2 network, each stretch of cable is connected to the [[Medium Attachment Unit|transceiver]] (which is usually built into the network adaptor) using a BNC [[T-connector]],{{efn|Other connectors such as [[EAD socket]]s were promoted as a less error-prone alternative to BNC connectors.}} 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 [[Transmission line|buses]], Ethernet segments have to be [[Electrical termination|terminated]] with a [[resistor]] at each end. Each end of the cable has a {{val|50|ul=Ω}} resistor attached. Typically this resistor is built into a male [[BNC connector|BNC]] and attached to the last device on the bus. This is most commonly connected directly to the T-connector on a workstation.{{efn|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 [[alternating current|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.

Some terminators have a metallic chain attached to them for grounding purposes. The cable should be [[ground (electricity)|grounded]] only at one end. Grounding the terminators at both may produce a [[Ground loop (electricity)|ground loop]] and can cause network outages or data corruption when swells of electricity traverse the coaxial cabling's outer shield.

When wiring a 10BASE2 network, special care has to be taken to ensure that cables are properly connected to all T-connectors. Bad contacts or shorts are especially difficult to diagnose. A failure at any point of the network cabling tends to prevent all communications. For this reason, 10BASE2 networks can be difficult to maintain and were often replaced by [[10BASE-T]] networks, which (provided [[category 5 cable]] or better was used) also provided a good upgrade path to [[100BASE-TX]].

==Comparisons to 10BASE-T==
10BASE2 networks cannot generally be extended without breaking service temporarily for existing users and the presence of many joints in the cable also makes them very vulnerable to accidental or malicious disruption. There were proprietary systems that claimed to avoid these problems (e.g. [[EAD socket]]s) but these never became widespread, possibly due to a lack of standardization. 10BASE-T can be extended by making a new connection to a hub. A fault in a one hub connection does not necessarily compromise other connections to the hub.

10BASE2 systems did have a number of advantages over 10BASE-T. No hub is required as with 10BASE-T, so the hardware cost was minimal, and wiring was particularly easy since only a single wire run is needed, which could be sourced from the nearest computer. These characteristics made 10BASE2 ideal for a small network of two or three machines, perhaps in a home where easily concealed wiring was an advantage. For a larger complex office network, the difficulties of tracing poor connections made it impractical. Unfortunately for 10BASE2, by the time multiple home [[computer network]]s became common, the format had already been practically superseded by 10BASE-T.

==Comparisons to 10BASE5, use of AUI==
10BASE2 uses [[RG-58|RG-58A/U]] cable or similar for a maximum segment length of 185&nbsp;m as opposed to the thicker [[RG-8]]-like cable used in [[10BASE5]] networks with a maximum length of 500&nbsp;m. The RG-58 type wire used by 10BASE2 was inexpensive, smaller and much more flexible than the specialized RG-8 variant. 10BASE2 can also use [[RG-59]] cable.<ref>{{cite book|url=https://books.google.com/books?id=752JrPawu_sC|page=12 |title=802.11 Wireless LAN Fundamentals |isbn=978-1-58705-077-0 |last1=Roshan |first1=Pejman |last2=Leary |first2=Jonathan |date=2004 |publisher=Cisco Press }}</ref><ref name="AN0620">{{cite web |last1=Rajabzadeh |first1=Mohammed |title=Interfacing the DP8392 to 93X and 75X Cable |url=http://bitsavers.informatik.uni-stuttgart.de/components/national/_appNotes/AN-0620.pdf |publisher=National Semiconductor |access-date=14 May 2024}}</ref>

An Ethernet [[network interface controller]] (NIC) may include the 10BASE2 transceivers and thus directly provide a 10BASE2 [[BNC connector]] (that the T-connector plugs into), or it may offer an [[Attachment Unit Interface|AUI]] connector that external transceivers (see [[Medium Attachment Unit]]) can connect to. These can be transceivers for 10BASE2, but also for 10BASE5 or 10BASE-T. Some NICs offer both BNC and AUI connectors, or other combinations including BNC and 10BASE-T. With multiple connections, only one connector is designed to be used at the same time.

==See also==
{{Commons category}}
* [[Classic Ethernet]]
* [[List of network buses]]

==Notes==
{{Noteslist}}

==References==
{{Reflist}}

{{Ethernet}}

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[[Category:Ethernet standards]]