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How the Internet works |
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On the Internet, when you want to retrieve a document from another computer, you request a service from this computer. Your computer is the client, the computer on which the information you want to access is stored, is called the  server. Therefore the Internet's architecture is called client-server architecture.
A common set of standards allows the exchange of data and commands independent from locations, time, and operating systems through the Internet. These standards are called communication protocols, or the Internet Protocol Suite, and are implemented in Internet software. Sometimes the Internet Protocol Suite is erroneously identified with TCP/IP (Transmission Control Protocol / Internet Protocol).
Any information to be transferred is broken down into pieces, so-called packets, and the Internet Protocol figures out how the data is supposed to get from A to B by passing through routers.
Each packet is "pushed" from router to router via gateways and might take a different route. It is not possible to determine in advance which ways these packets will take. At the receiving end the packets are checked and reassembled.
The technique of breaking down all messages and requests into packets has the advantage that a large data bundle (e.g. videos) sent by a single user cannot block a whole network, because the bandwidth needed is deployed on several packets sent on different routes. Detailed information about routing in the Internet can be obtained at  http://www.scit.wlv.ac.uk/~jphb/comms/iproute.html.
One of the Internet's (and of the Matrix's) beginnings was the ARPANet, whose design was intended to withstand any disruption, as for example in military attacks. The ARPANet was able to route data around damaged areas, so that the disruption would not impede communication. This design, whith its origin in strategic and military considerations, remained unchanged for the Internet. Yet the design of the ARPANet's design cannot be completely applied to the Internet.
Routing around depends on the location of the interruption and on the availability of intersecting points between networks. If, for example, an E-mail message is sent from Brussels to Athens and in Germany a channel is down, it will not affect access very much, the message will be routed around this damage, as long as a major Internet exchange is not affected. However, if access depends on a single backbone connection to the Internet and this connection is cut off, there is no way to route around.
In most parts of the world the Internet is therefore vulnerable to disruption. "The idea of the Internet as a highly distributed, redundant global communications system is a myth. Virtually all communications between countries take place through a very small number of bottlenecks, and the available bandwidth isn't that great," says Douglas Barnes. These bottlenecks are the network connections to neighboring countries. Many countries rely on a one single connection to the Net, and in some places, such as the Suez Canal, there is a concentration of fiber-optic cables of critical importance.
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Bandwidth
The bandwidth of a transmitted communications signal is a measure of the range of frequencies the signal occupies. The term is also used in reference to the frequency-response characteristics of a communications receiving system. All transmitted signals, whether analog or digital, have a certain bandwidth. The same is true of receiving systems.
Generally speaking, bandwidth is directly proportional to the amount of data transmitted or received per unit time. In a qualitative sense, bandwidth is proportional to the complexity of the data for a given level of system performance. For example, it takes more bandwidth to download a photograph in one second than it takes to download a page of text in one second. Large sound files, computer programs, and animated videos require still more bandwidth for acceptable system performance. Virtual reality (VR) and full-length three-dimensional audio/visual presentations require the most bandwidth of all.
In digital systems, bandwidth is data speed in bits per second (bps).
Source: Whatis.com
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