ch11 - Chapter 11: Advanced Text Techniques: Web and...

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Unformatted text preview: Chapter 11: Advanced Text Techniques: Web and Information 1 2 Networks: Two or more computers communicating Networks are formed when distinct computers communicate via some mechanism. Rarely does the communication take the place of 0/1 voltages over a wire. Too hard to make work over distances More common is the use of frequencies (maybe in the sound range, but maybe not). For example, a modem (modulator-demodulator) takes your computers 0s and 1s and translates them into sound frequencies that can pass over the sound wire and be decoded on the other side. 3 Networks, networks everywhere If youre driving a newer car, you probably have a network in there. There are lots of computers in your car (controlling air flow, gas flow; making the air bag work) and they communicate. You can have a network in your own home, or even on an airplane. Can use radio signals for communication (wireless) Or can string a cable between two computers. 4 Networks have layers Networks have several layers to them. At the bottom level is the physical substrate. What are the signals being passed on? Levels higher determine how data is encoded. Do we use sound frequencies to represent 0s and 1s, or radio waves? Do we send a bit at a time? A byte at a time? Or in packets larger than that? Levels even higher determine the protocol of communication. How do I address a particular computer I want to talk to? Or many computers? How do I tell a computer that I want to talk to it? That Im starting to send it data? What its supposed to do with it? When are we done? 5 Ethernet: A common mid-level protocol Ethernet is a common mid-level protocol. It specifies some aspects of how data is encoded and computers are specified. For example, each computer on an Ethernet network has a deep-down inside-the-computer address that identifies it uniquely. But Ethernet can work over a variety of physical substrates. For example, you can run Ethernet over wireless (radio) or over coaxial cable (where you hear terms like 10baseT 6 Internet: A collection of networks The Internet is a network of networks. If you put a device in your home so that your computers can talk to one another, you have a network. A wireless base station, or an Ethernet router , perhaps. You can probably reach printers on your network, or copy files between computers. If you now connect your network (through an Internet Service Provider (ISP)) to the global Internet, your network becomes yet another part of the whole Internet. 7 Internet is based on agreements on encodings The Internet is built on a set of agreements about: How computers will be addressed A set of four numbers (each one byte now, soon to grow) separated by periods, e.g., 210.51.40.155....
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ch11 - Chapter 11: Advanced Text Techniques: Web and...

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