Ethernet is a protocol of Lan to Packet switching. Although it implements the physical Layer (PHY) and the underlayer Media Access Control (MAC) of OSI model, the Ethernet protocol is classified in the Course binder, because the formats of screens which the standard defines are standardized and can be encapsulated in protocols other than its own physical layers MAC and PHY. These physical layers are the subject of standards separated according to the flows, of the support of transmission, the length of the connections and the environmental conditions.
Ethernet was standardized under the name IEEE 802.3 . It is now an international standard: ISO/CIE 8802-3 .
Since the Years 1990, one very frequently uses Ethernet on twisted pairs for the connection of the stations customers, and the versions on Fiberoptic for the heart of the network. This configuration largely supplanted other standards like the Token-ring, FDDI and ARCNET. For a few years, the alternatives wireless telegraphy of Ethernet (standards IEEE 802.11, known as “WiFi”) have been a strong success, as well on the personal installations as professional.
The name Ethernet comes from its ancestor ALOHAnet who used waves radio frequencies. However one formerly said these last that they were propagated in the ether , mythical medium in which was supposed to bathe the Universe. As for the suffix Net , it is about the abbreviation of the word “network” in English.
Ethernet was originally developed like one of the pioneers projects of the Xerox PARK. A common history wants that he was invented in 1973, date on which Bob Metcalfe wrote a memo with its owners in connection with the potential of Ethernet. Metcalfe affirms that Ethernet has in fact invented over one period of several years. In 1976, Robert Metcalfe and David Boggs (the assistant of Metcalfe) published an headed document Ethernet: Distributed Packet-Switching For Local Computer Networks (Ethernet: packet switching distributed for the local data-processing networks).
Metcalfe left Xerox in 1979 to promote the use of the personal computers and the lans, and founded the company 3Com. It succeeds in convincing DEC, Intel and Xerox to work together to promote Ethernet as a standard. Ethernet was at the time in competition with two owner systems, Token-ring and ARCnet, but these two systems quickly decreased in popularity vis-a-vis Ethernet. During this time, 3Com became a major company of the field of the data-processing networks.
Ethernet is based on the principle of members (even) on the network, sending messages in what was primarily a radio operator, captive system inside a wire or of a common channel, sometimes called the ether . Each par is identified by an overall single key, called Adresse MAC, to make sure that all the stations on an Ethernet network have distinct addresses.
A technology known under the name of Judicious Carrier Multiple Access with Collision Detection (Listening of carrying with multiple accesses and collision detection) or CSMA/CD governs the way in which the stations reach the media. At the beginning developed during the Years 1960 for ALOHAnet with Hawaii by using the radio, technology relatively simple is compared with Token-ring or the networks controlled by a Master. When a computer wants to send information, he obeys the algorithm according to:
If the media are not used, to start transmission, if not to go to stage 4
- from information If a collision is detected, continuous to transmit until minimal time for a package is exceeded (to make sure that all the stations detect the collision), then to go at stage 4
- of a successful transmission Indiquer the success to the protocol of the higher level and to leave the mode of transfer.
- occupied To wait until the wire is unutilised.
- cable is become again free Attendre during a random time, then to turn over at stage 1, except if the maximum number of tests of transmission were exceeded.
- maximum of tests of transmission exceeded To announce the failure with the protocol of higher level and to leave the mode of transmission.
In practice, this functions like an ordinary discussion, where people use a whole a common medium (air) to speak with someone else. Before speaking, each person waits politely until nobody any more speaks. If two people start to speak at the same time, both stop and wait a short random time. There are good lucks that the two people await a different time, thus avoiding another collision. Exponential latencies are used when several collisions occur after.
As in the case of a network not commutated, all the communications are emitted on a shared medium, any information sent by a station is received by all the others, even if this information were intended for only one person. The computers connected on Ethernet must thus filter what is intended to them or not. This type of communication “somebody speaks, all the others hear” of Ethernet is one of its weaknesses, because, while one of the nodes emits, all the machines of the network receive and must, on their side, to observe silence. With the result that a communication with strong flow between only two stations can saturate a whole lan.
In the same way, as the chances of collision are proportional to the number of transmitters and with the data sent, the network becomes extremely congested beyond 50 % of its capacity (independently of the number of sources of traffic). To solve this problem, the switches were developed in order to maximize the Band-width available.
According to the flow used, it is necessary to take account of the field of collision governed by the laws of physics and in particular electronic displacement in a copper cable. If one does not respect these maximum distances between machines, protocol CSMA/CD does not take place to exist.
The same if a switch is used, CSMA/CD is decontaminated. And this for a reason which one includes/understands well. With CSMA/CD, one listens to what one emits, if somebody speaks at the same time as me there is collision. There is thus incompatibility with the full-duplex mode of the switches.
Types of Ethernet screens and field EtherType
There are four types of Ethernet screen:
- Ethernet original version I (is not used any more)
- Ethernet Version 2 or Ethernet II (called screen TEN, always used)
- IEEE 802.x LLC
- IEEE 802.x LLC/SNAP
These various types of screen have formats and values of different MTU but can coexist on the same physical medium.
Original version 1 of Xerox has a field of 16 bits identifying the size of screen, even if the maximum length of a screen were of 1500 Octet S. This field was quickly re-used in version 2 of Xerox like field of identification, with convention that values between 0 and 1500 indicated screen Ethernet original, but that the larger values indicated what was called the EtherType, and the use of the new format of screen. This is now taken charges with them in the protocols IEEE 802 by using the Entête SNAP.
The IEEE 802.x again defined the field of 16 bits after the MAC addresses like the length. As Ethernet I is not used any more, this makes it possible the software to determine if a screen is of type Ethernet II or IEEE 802.x, allowing the cohabitation of the two standards on the same physical medium. All the screens 802.x have a field LLC. By examining this last, it is possible to determine if it is followed by a field SNAP or not.
Image extracted the document of G.Requilé of CNRS
Integrality of the document on: http://www.lmgc.univ-montp2.fr/~requile/documents/reseau/LLC.pdf
Attention there exist other types of Ethernet screens specifying the length in particular as well as other characteristics. With for the fields Standard of protocol following values:
0x0800 : IPv4
- 0x86DD : IPv6
- 0x0806 : ARP
- 0x8035 : RARP
- 0x0600: XNS
- 0x809B: Appletalk
- One will note the presence sometimes preamble to 64 bits from synchronization, alternation of 1 and 0 with the last two bits with 1. (not represented on the screen).
- the address of broadcast ( diffusion ) Ethernet has all its bits with 1
- the minimal size of the data is of 46 bytes ()
Varieties of Ethernet
The section below gives a short summary of all the types of media of Ethernet. In addition to all these official standards, several salesmen implemented types of media owners for various reasons -- sometimes to support moreover long distances on Fiberoptic.
Some old varieties of Ethernet
- Xerox Ethernet -- Original implementation of Ethernet, which had two versions, version 1 and 2, during its development. Version 2 is still often used.
- 10BASE5 (also called Thick Ethernet ) -- This standard of the IEEE published very early uses a simple Coaxial cable in which one inserts a connection by boring the cable to connect oneself to the center and the mass (taken vampires ). Largely obsolete, but because of several large installations carried out very early, some systems can still be of use.
- 10BROAD36 -- Obsolete. An old standard supporting Ethernet on long distances. It used techniques of modulation in Broad band similar to those employed by the cable modems, operated on a coaxial cable.
- 1BASE5 -- An attempt at standardization of solution for lans at low prices. It operates to 1 Mbit/s but was a commercial failure.
Ethernet 10 Mbit/s
- 10BASE2 (also called ThinNet or Cheapernet ) -- a coaxial cable of 50 Ohm S connects the machines together, each machine using an adapter in T to connect with its Carte network. A termination with each end requires. During several years, it was the Ethernet standard dominating.
- 10BaseT -- Function with 4 wire (two twisted pairs) on a cable CAT-3 or CAT-5 with connector RJ45. A Concentrating (or hub) or a switch (or switch) is in the center of the network, having a port for each node. It is also the configuration used for the 100BASE-T and the Gigabit Ethernet (cable CAT-6). Although the presence of a central node (the hub) gives a visual impression of topology out of star, it is however well about a bus topology - all the emitted signals are received by the whole of the connected machines. Star topology appears only if one uses a switch (switch).
- FOIRL -- Fiber-optic inter-repeater link (bond inter-repeater on fiberoptic). The original standard for Ethernet on the Fiberoptic.
- 10BASE-F -- Generic term for the new family of Ethernet 10 Mbit/s: 10BASE-FL, 10BASE-BFR and 10BASE-FP. Those, only 10BASE-FL is used much.
- 10BASE-FL -- One setting-with-day of standard FOIRL.
- 10BASE-BFR -- Envisaged to inter-connect concentrators or switches in the middle of the network, but now obsolete.
- 10BASE-FP -- A star shaped network which did not require any repeater, but which forever be carried out.
Fast Ethernet (100 Mbit/s)
- 100BASE-TX -- Use two pairs and requires cable CAT-5. Star topology by using a concentrator (hub) or a switch (switch), as for the 10BaseT, with which it is compatible.
- 100BASE-T4 -- 100 Mbit/s allows (out of semi-duplex only) on cable CAT-3 (which was used in installations 10BaseT). Use the four pairs of the cable. Now obsolete, as the CAT-5 is the current standard.
- 100BASE-T2 -- No product exists. Support the full-duplex mode and uses only two pairs, with cables CAT-3. It is equivalent to the 100BASE-TX on the plan of the functionalities, but supports the old cables.
- 100BASE-FX -- Ethernet 100 Mbit/s on fiberoptic.
Gigabit Ethernet (: 1000 Mbit/s)
1000BASE-T -- 1 Gbit/s on cable of twisted pairs of the category 5th or higher, over a maximum length of 100m. Use the 4 pairs in full duplex, each pair transmitting 2 bits/s by baud, using a code at 5 times. That is to say a total of 1 byte by signal of clock on all 4 pair, in each direction. Compatible with 100BASE-TX and 10BaseT, automatic control of Tx and X-ray assured. Topology is here always out of star because there do not exist concentrators 1000 Mbps. One thus uses obligatorily switches (switch).
- 1000BASE-X -- 1 Gbit/s which uses modular interfaces (called GBIC) adapted to the media (Fiberoptic Multi, Mono-mode, copper).
- 1000BASE-SX -- 1 Gbit/s on fiberoptic multimode with 850nm.
- 1000BASE-LX -- 1 Gbit/s on fiberoptic monomode and multimode with 1300nm.
- 1000BASE-LH -- 1 Gbit/s on fiberoptic, long distances.
- 1000BASE-ZX -- 1 Gbit/s on fiberoptic monomode long distances.
- 1000BASE-CX -- A solution for short distances (up to 25 m) for the 1 Gbit/s on special copper cable. Precede 1000BASE-T and is now obsolete.
Ethernet 10 gigabit a second
The new standard Ethernet 10 Gigabits surrounds seven different types of media for the lans, underground railway networks and wide area networks. It is currently specified by an additional standard, the IEEE 802.3ae, and will be built-in a future revision of the IEEE 802.3.
10GBASE-CX4 (copper, cable infiniband, 802.3ak) -- use a copper cable of the type infiniband 4x over a maximum length of 15 meters.
- 10GBASE-T -- transmission on cable 6,6A category or 7 (802.3an), in full duplex on 4 pairs with a number of moments of coding which will be function of the category retained for the cable (and of immunity to the noise wished), over a maximum length of 100 meters. Should be compatible with 1000BASE-T, 100BASE-TX and 10BaseT
- 10GBASE-SR (850nm MM, 300 meter, dark fiber) -- created to support short distances on multimode fiberoptic, it has a range from 26 to 82 meters, according to the type of cable. It supports also the distances up to 300 m on the new multimode fiber 2000 MHz.
- 10GBASE-LX4 -- use the Multiplexage by division wavelength to support distances between 240 and 300 meters on multimode fiber. Also support up to 10 km with monomode fiber.
- 10GBASE-LR (1310nm SM, 10km, dark fiber) and 10GBASE-ER (1550nm SM, 40km, dark fiber) -- These standards support up to 10 and 40 km respectively, on monomode fiber.
- 10GBASE-SW (850nm MM, 300 meter, SONNET), 10GBASE-LW (1310nm SM, 10km, SONNET) and 10GBASE-EW (1550nm SM, 40km SONNET). These varieties use WAN PHY , being conceived inter-to operate with equipment OC-192/STM-64 SONNET/SDH. They correspond at the physical level to 10GBASE-SR, 10GBASE-LR and 10GBASE-ER respectively, and use the same type of fiber, in addition to supporting the same distances. (There is no standard WAN PHY corresponding to the 10GBASE-LX4.)
Ethernet 10 Gigabits is rather recent, and it remains to see which standards will obtain the acceptance of the companies.
Technical details of 10GBASE-R used on LAN & 10GBASE-W used on WAN and encapsulating Ethernet in a screen SDH or SONNET.
- PBT/PBB-TE Ethernet technology used in the networks of operators
- CPL for Powerline communication
- AFDX (Duplex Avionics Full) Ethernet network redundant and made reliable
- FSFB2 (Fail Safe Field Drunk 2nd generation) Sedentary Protocol for network Ethernet
- http://web.archive.org/web/20030613072801/www.10gea.org/ Web site of the 10 Gigabit Ethernet Alliance
- http://www.commentcamarche.net/technologies/ethernet.php3 Introduction to Ethernet
- http://www.polymorphe.org/telecharger-53-cours-Ethernet Course Ethernet
- http://www.polymorphe.org/telecharger-52-cours-Fast-Ethernet Course Fast Ethernet
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