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Two multi-mode optical fiber, 2 km maximum
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In the late 1980s, 10 Mbps became too slow for some applications and network manufacturers developed several LAN technologies that offered higher bandwidth, such as the 100 Mbps FDDI LAN that used optical fibers. As the development of 10Base5, 10Base2 and 10BaseT had shown that Ethernet could be adapted to different physical layers, several manufacturers started to work on 100 Mbps Ethernet and convinced IEEE to standardize this new technology that was initially called `Fast Ethernet`. `Fast Ethernet` was designed under two constraints. First, `Fast Ethernet` had to support twisted pairs. Although it was easier from a physical layer perspective to support higher bandwidth on coaxial cables than on twisted pairs, coaxial cables were a nightmare from deployment and maintenance perspectives. Second, `Fast Ethernet` had to be perfectly compatible with the existing 10 Mbps Ethernet to allow `Fast Ethernet` technology to be used initially as a backbone technology to interconnect 10 Mbps Ethernet networks. This forced `Fast Ethernet` to use exactly the same frame format as 10 Mbps Ethernet. This implied that the minimum `Fast Ethernet` frame size remained at 512 bits. To preserve CSMA/CD with this minimum frame size and 100 Mbps instead of 10 Mbps, the duration of the `slot time` was decreased to 5.12 microseconds.
The evolution of Ethernet did not stop. In 1998, the IEEE published a first standard to provide Gigabit Ethernet over optical fibers. Several other types of physical layers were added afterwards. The `10 Gigabit Ethernet <http://en.wikipedia.org/wiki/10_gigabit_Ethernet>`_ standard appeared in 2002. Work is ongoing to develop `standards <http://www.ieee802.org/3/ba/public/index.html>`_ for 40 Gigabit and 100 Gigabit Ethernet and some are thinking about `Terabit Ethernet <http://www.networkworld.com/news/2009/042009-terabit-ethernet.html>`_. The table below lists the main Ethernet standards. A more detailed list may be found at http://en.wikipedia.org/wiki/Ethernet_physical_layer.
Standard
Comments
10Base5
Thick coaxial cable, 500m
10Base2
Thin coaxial cable, 185m
10BaseT
Two pairs of category 3+ UTP
10Base-F
10 Mb/s over optical fiber
100Base-Tx
Category 5 UTP or STP, 100 m maximum
100Base-FX
Two multi-mode optical fiber, 2 km maximum
1000Base-CX
Two pairs shielded twisted pair, 25m maximum
1000Base-SX
Two multi-mode or single mode optical fibers with lasers
10 Gbps
Optical fiber but also Category 6 UTP
40-100 Gbps
Optical fiber (experiences are performed with copper)
Footnotes
Additional information about the history of the Ethernet technology may be found at http://ethernethistory.typepad.com/
Initially, the OUIs were allocated by Xerox [DP1981]_. However, once Ethernet became an IEEE and later an ISO standard, the allocation of the OUIs moved to IEEE. The list of all OUI allocations may be found at http://standards.ieee.org/regauth/oui/index.shtml
The official list of all assigned Ethernet type values is available from http://standards.ieee.org/regauth/ethertype/eth.txt
The attentive reader may question the need for different `EtherTypes` for IPv4 and IPv6 while the IP header already contains a version field that can be used to distinguish between IPv4 and IPv6 packets. Theoretically, IPv4 and IPv6 could have used the same `EtherType`. Unfortunately, developers of the early IPv6 implementations found that some devices did not check the version field of the IPv4 packets that they received and parsed frames whose `EtherType` was set to `0x0800` as IPv4 packets. Sending IPv6 packets to such devices would have caused disruptions. To avoid this problem, the IETF decided to apply for a distinct `EtherType` value for IPv6. Such a choice is now mandated by :rfc:`6274` (section 3.1), although we can find a funny counter-example in :rfc:`6214`.
These network interfaces compute the TCP checksum while a segment is transferred from the host memory to the network interface [SH2004]_.
Fortunately, IEEE was able to define the [IEEE802.3]_ frame format while maintaining backward compatibility with the Ethernet [DIX]_ frame format. The trick was to only assign values above 1500 as `EtherType` values. When a host receives a frame, it can determine whether the frame's format by checking its `EtherType/Length` field. A value lower smaller than `1501` is clearly a length indicator and thus an [IEEE802.3]_ frame. A value larger than `1501` can only be type and thus a [DIX]_ frame.
Component Translation Difference to current string
This translation Propagated Empty cnp3-ebook/protocols/ethernet
The following string has the same context and source.
Propagated Empty cnp3-ebook/protocols/lan

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cnp3-ebook / protocols/ethernet — French

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Source string location
../../protocols/ethernet.rst:176
String age
2 years ago
Source string age
2 years ago
Translation file
locale/fr/LC_MESSAGES/protocols/ethernet.po, string 39