How ethernet Works ?
Not so long ago, computers were all made by different companies, worked in different ways, and couldn't communicate with one another. Often, they didn't even have the same sorts of plugs and sockets on their cases! During the 1980s and 1990s, everything became much more standardized and it's now possible to connect virtually any machine to any other and get them exchanging data without too much effort. That's largely because most networks now use the same system, called Ethernet. It was developed in May 1973 by US computer engineer Dr Robert ("Bob") Metcalfe (1946–), who went on to found 3Com and later became a well-known computer-industry pundit (perhaps, somewhat unfairly, best known for predicting a spectacular collapse of the Internet in 1995 that never actually occurred).
As Metcalfe originally designed it, Ethernet was based on three very simple ideas. First, computers would connect through the "ether" (a semi-serious, semi-scientific name for the void of emptiness that separates them) using standard coaxial cable (wires like the ones used in a television antenna connection, made up of concentric metal layers). In Ethernet-speak, the physical connection between the nodes (computers and other devices) on the network is also known as the medium. Things have moved on quite a bit since the early 1970s and the medium is now just as often a wireless radio link (you've probably heard of Wi-Fi, which is the wireless version of Ethernet). Second, all the computers and devices on a network would stay silent except for when they were sending or receiving messages. Finally, when they wanted to communicate, they'd do so by breaking up messages into small packets of data and sending them around the network by a highly efficient method known as packet switching (discussed in much more detail in our article on the Internet).
If one machine wants to send a message to another machine on an Ethernet network, it goes through a process a bit like sending a letter. The message has to be packaged in a standard format called a frame (a bit like the envelope that contains a letter). The frame includes a standard header, the address of the device on the network it's intended for (like the address on an envelope), the address of the machine that sent it (like an envelope's return-to or sender's address), an indication of how much data it contains, the data itself, some padding, and some error checking information at the end (used to do a quick check on whether the data has transmitted correctly). Unlike a letter, which goes only to the recipient, the frame goes to every machine and device on the network. Each machine reads the destination address to figure out whether the frame is intended for them. If so, they act on it; if not, they ignore it. Any machine on the network can transmit messages through the ether at any time, but problems will occur if two or more machines try to talk at once (known as a collision). If that happens, the machines all fall silent for a random period of time before trying again. Eventually, one will find the ether is clear and get its message out first, followed by the other, so all messages will get through eventually. Typical Ethernet equipment can handle thousands of frames per second. In tech-speak, this method of using the network is called carrier sense multiple access with collision detection (CSMA/CD): that's a fancy way of saying that the nodes do their best to transmit when the ether is clear ("carrier sense"), they can all theoretically send or receive at any time ("multiple access"), and they have a way of sorting out the problem if two happen to transmit at exactly the same time ("collision detection").
As Metcalfe originally designed it, Ethernet was based on three very simple ideas. First, computers would connect through the "ether" (a semi-serious, semi-scientific name for the void of emptiness that separates them) using standard coaxial cable (wires like the ones used in a television antenna connection, made up of concentric metal layers). In Ethernet-speak, the physical connection between the nodes (computers and other devices) on the network is also known as the medium. Things have moved on quite a bit since the early 1970s and the medium is now just as often a wireless radio link (you've probably heard of Wi-Fi, which is the wireless version of Ethernet). Second, all the computers and devices on a network would stay silent except for when they were sending or receiving messages. Finally, when they wanted to communicate, they'd do so by breaking up messages into small packets of data and sending them around the network by a highly efficient method known as packet switching (discussed in much more detail in our article on the Internet).
If one machine wants to send a message to another machine on an Ethernet network, it goes through a process a bit like sending a letter. The message has to be packaged in a standard format called a frame (a bit like the envelope that contains a letter). The frame includes a standard header, the address of the device on the network it's intended for (like the address on an envelope), the address of the machine that sent it (like an envelope's return-to or sender's address), an indication of how much data it contains, the data itself, some padding, and some error checking information at the end (used to do a quick check on whether the data has transmitted correctly). Unlike a letter, which goes only to the recipient, the frame goes to every machine and device on the network. Each machine reads the destination address to figure out whether the frame is intended for them. If so, they act on it; if not, they ignore it. Any machine on the network can transmit messages through the ether at any time, but problems will occur if two or more machines try to talk at once (known as a collision). If that happens, the machines all fall silent for a random period of time before trying again. Eventually, one will find the ether is clear and get its message out first, followed by the other, so all messages will get through eventually. Typical Ethernet equipment can handle thousands of frames per second. In tech-speak, this method of using the network is called carrier sense multiple access with collision detection (CSMA/CD): that's a fancy way of saying that the nodes do their best to transmit when the ether is clear ("carrier sense"), they can all theoretically send or receive at any time ("multiple access"), and they have a way of sorting out the problem if two happen to transmit at exactly the same time ("collision detection").
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