What Is A Ethernet Protocol
What Is A Ethernet Protocol?
Ethernet is a protocol for local network packet. Although it implements the physical layer (PHY) and the sub-layer Media Access Control (MAC) of the OSI model, the Ethernet protocol is listed in the link layer, because the frame formats that are standard defines standardized and may be encapsulated in protocols other than its own physical layer MAC and PHY. These physical layers are the subject of separate standards based on rates of transmission medium, the bond lengths and environmental conditions.
Ethernet has been standardized as the IEEE 802.3. It is now an international standard: ISO / IEC 8802-3.
Since the 1990s, is used very frequently Ethernet over twisted pair for connecting client, and fiber optic versions for the heart of the network. This configuration has largely superseded other standards such as Token Ring, FDDI, and ARCNET. In recent years, variants of wireless Ethernet (IEEE 802.11 standards, called “Wi-Fi”) have been highly successful, both on personal and professional installations.
In an Ethernet network, cable broadcast data to all connected machines, the same way that radio waves reach all receivers. The name derives from the Ethernet analogy [1]: Before the twentieth century it was thought that the waves propagated in the ether, supposed hypothetical medium bathing the universe. As the net suffix, this is the abbreviation of the word network (network) in English.
History of Ethernet
Ethernet was originally developed as a pioneer project of Xerox PARC. A common history is that he invented in 1973, when Bob Metcalfe wrote a memo to his bosses about the potential of Ethernet. Metcalfe says that Ethernet has actually been invented over many years. In 1976, Robert Metcalfe and David Boggs (assistant Metcalfe) has published a document entitled Ethernet: Distributed Packet-Switching For Local Computer Networks (Ethernet: distributed packet switching for local computer networks).
Metcalfe left Xerox in 1979 to promote the use of personal computers and local networks, and founded the company 3Com. He convinced DEC, Intel and Xerox to work together to promote Ethernet as standard. Ethernet at the time was competing with two proprietary systems, Token Ring and ARCnet, but both systems have rapidly declined in popularity in the face to the Ethernet. Meanwhile, 3Com became a major company in the field of computer networks.
Ethernet: General Description
Ethernet is based on the principle of members (peers) on the network, sending messages in what was essentially a radio system, captive inside a wire or a common channel, sometimes called the ether. Each pair is identified by a globally unique key, called MAC address, to ensure that all stations on an Ethernet have distinct addresses.
A technology known as Carrier Sense Multiple Access with Collision Detection (carrier sense multiple access with collision detection) or CSMA / CD governs how access to media posts. Initially developed during the 1960s ALOHAnet Hawaii using radio technology is relatively simple compared to Token Ring or networks controlled by a master. When a computer wants to send information, it obeys the following algorithm:
1. If the media is not used, start the transmission, otherwise go to step 4
2. [Transmission of Information] If a collision is detected, continue transmitting until the minimum time for a packet is passed (to ensure that all stations detect the collision), then go to step 4
3. [end of a successful transmission] indicate the success of the protocol level and exit transfer.
4. [Cable occupied] Wait until the wire is unused.
5. [the cable is again free] Wait a random time, then return to Step 1 unless the maximum number of test transmissions has been exceeded.
6. [maximum transmission tests exceeded] the failure to Announce higher level protocol and exit transmission.
In practice, this works like a regular discussion, where people all use a common medium (air) to speak to someone else. Before speaking, each person waits politely that no one speaks. If two people start talking at the same time, both stop and wait a short random time. There are good chances that two people waiting for a different period, thus avoiding another collision. Waiting times are exponential used when multiple collisions occur as a result.
As in the case of a non-switched network, all communications are issued on a shared medium, any information sent by mail is received by all others, even if such information was intended for one person. Computers connected to the Ethernet must filter what they are intended or not. This type of communication “someone speaks, all other mean” Ethernet is one of his weaknesses, for while one node makes all the machines on the network must receive and, in turn, observe the silence. What makes a high-speed communication between only two positions can saturate an entire LAN.
Similarly, as the chances of collision are proportional to the number of transmitters and the data sent, the network becomes extremely congested beyond 50% capacity (regardless of the number of traffic sources). To resolve this problem, switches have been developed to maximize the available bandwidth.
Depending on the rate used should take into account the collision domain governed by the laws of physics and in particular the electronic movement in a copper cable. If you do not respect these maximum distances between machines, Protocol CSMA / CD is no reason to exist.
Similarly if we use a switch, CSMA / CD is disabled. And for this reason that we understand well. With CSMA / CD, we hear what the issues are, if someone speaks the same time as me there is a collision. It is therefore incompatible with full-duplex switches.
Types of Ethernet frames and field EtherType
There are four Ethernet frame types:
* Original Ethernet Version I (no longer used)
* Ethernet Version 2 or Ethernet II (DIX called frame, still used)
* IEEE 802.x LLC
* EE 802.x * LLC / SNAP
These different frame types have different formats and MTU values of different but can coexist on the same physical medium.
Version 1 Original Xerox has a field of 16 bits identifying the frame size, although the maximum length of a frame was 1 500 bytes. This field was quickly reused in version 2 of Xerox as a field of identification, with the convention that values between 0 and 1 500 showed an original Ethernet frame, but that larger values indicated what was called the EtherType, and use the new frame format. This dual use of the same data field justifies its common name field length / type.
The IEEE 802.3 has defined the new field after the 16-bit MAC address as the length. As the Ethernet I no longer used, this now allows software to determine if a frame is Ethernet II or IEEE 802.3, allowing the coexistence of two standards on the same physical medium. All 802.3 frames have a field LLC. In examining the latter, it is possible to determine if it is followed by a SNAP field or not.
Study: From Wikipedia, the free encyclopedia. The text is available under the Creative Commons.
