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10BASE2
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10BASE2 (also known as cheapernet,[1] thin Ethernet, thinnet, and thinwire) is a variant of Ethernet that uses thin coaxial cable terminated with BNC connectors to build a local area network. During the mid to late 1980s, this was the dominant 10 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 Mbit/s. In 1995, the Fast Ethernet standard upgraded the speed to 100 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.[2] As of 2011, IEEE 802.3 has deprecated this standard for new installations.[3]
Name origination
[edit]The name 10BASE2 is derived from several characteristics of the physical medium. The 10 comes from the transmission speed of 10 Mbit/s. The BASE stands for baseband signaling, and the 2 for a maximum segment length approaching 200 m (the actual maximum length is 185 m).
Signal encoding
[edit]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. Manchester coding allows the clock to be recovered from the signal. However, the additional transitions associated with it double the signal bandwidth.
Network design
[edit]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[4] with a minimum distance of 0.5 metres (20 in) between devices.[5] 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,[a] 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 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.[b] 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.
Some terminators have a metallic chain attached to them for grounding purposes. The cable should be grounded only at one end. Grounding the terminators at both may produce a 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
[edit]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 sockets) 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 networks became common, the format had already been practically superseded by 10BASE-T.
Comparisons to 10BASE5, use of AUI
[edit]10BASE2 uses RG-58A/U cable or similar for a maximum segment length of 185 m as opposed to the thicker RG-8-like cable used in 10BASE5 networks with a maximum length of 500 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.[6][7]
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 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
[edit]Notes
[edit]- ^ Other connectors such as EAD sockets were promoted as a less error-prone alternative to BNC connectors.
- ^ 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.
References
[edit]- ^ Alex Djenguerian (June 1986). "Ethernet/Cheapernet Physical Layer Made Easy with DP8391/92" (PDF). National Semiconductor. Archived (PDF) from the original on 2022-10-09. Retrieved 2019-08-13.
- ^ "L-com Introduces Commercial-Grade Thinnet (10Base-2) and Thicknet (10Base-5) Converters for Legacy Installs". L-com, Inc. 2012-06-11. Retrieved 2012-07-01.
- ^ IEEE 802.3-2012 10. Medium attachment unit and baseband medium specifications, type 10BASE2
- ^ IEEE 802.3 10.7.2.2 MAU placement
- ^ IEEE 802.3 10.7.2.1 Cable sectioning
- ^ Roshan, Pejman; Leary, Jonathan (2004). 802.11 Wireless LAN Fundamentals. Cisco Press. p. 12. ISBN 978-1-58705-077-0.
- ^ Rajabzadeh, Mohammed. "Interfacing the DP8392 to 93X and 75X Cable" (PDF). National Semiconductor. Retrieved 14 May 2024.
10BASE2
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Naming and standards
The nomenclature "10BASE2" encapsulates the essential attributes of this Ethernet variant. The "10" signifies the nominal data signaling rate of 10 megabits per second, while "BASE" indicates baseband signaling, where the entire bandwidth of the medium is used to transmit a single digital signal. The "2" approximates the maximum length of a network segment at 200 meters, though the precise electrical limit is 185 meters to ensure signal integrity. 10BASE2 was standardized as part of the IEEE 802.3 family of specifications for local area networks, specifically through the supplement IEEE 802.3a, approved on November 15, 1985, which added Clause 10 defining the physical layer for thin coaxial cable media.[10] This amendment positioned 10BASE2 as a cost-effective evolution of the original thick coaxial Ethernet, maintaining full compatibility with the Ethernet II frame format developed by Xerox, Intel, and DEC.[11] At its core, 10BASE2 relies on the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) medium access control protocol, which governs shared-medium contention and collision resolution across the network, as outlined in the foundational IEEE 802.3 standard.[11]Key specifications
10BASE2 operates at a data rate of 10 megabits per second (Mbps) in half-duplex mode, utilizing baseband signaling for transmission.[8] Each network segment supports a maximum length of 185 meters, using 50-ohm coaxial cable with specified attenuation limits to maintain signal integrity, ensuring a maximum of 8.5 dB loss at 10 MHz over the full segment distance.[1] The standard limits the number of stations to a maximum of 30 per segment to minimize collision probability and manage loading.[12] Under the 5-4-3 rule, a 10BASE2 network can incorporate up to five segments connected by four repeaters, with only three segments populated by nodes, resulting in a maximum total cable length of 925 meters across the collision domain.[13] Transceivers for 10BASE2 are powered either through the Attachment Unit Interface (AUI) cable from the data terminal equipment or via external power supplies, with typical consumption around 200 mA at 12 VDC.[14]| Specification | Value | Notes |
|---|---|---|
| Data rate | 10 Mbps | Half-duplex, baseband |
| Segment length | 185 m max | Per coaxial segment |
| Nodes per segment | 30 max | Including minimum 0.5 m spacing |
| Network extent | 925 m total | Up to 5 segments via 4 repeaters (5-4-3 rule) |
| Cable impedance | 50 ohms | RG-58 coaxial |
| Transceiver power | ~200 mA @ 12 VDC | Via AUI or external supply |