Circuit Switching and Packet Switching Networks
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In my grand overview of networking, I describe networks as devices that are connected together using special hardware and software, to allow them to exchange information. The most important word in that sentence is the final one: information. As you will see in your exploration of this Guide, there are many methods for exchanging information between networked devices. There are also a number of ways of categorizing and describing these methods and the types of networks that use them.
One fundamental way of differentiating networking technologies is on the basis of the method they use to determine the path between devices over which information will flow. In highly simplified terms, there are two approaches: either a path can be set up between the devices in advance, or the data can be sent as individual data elements over a variable path.
In this networking method, a connection called a circuit is set up between two devices, which is used for the whole communication. Information about the nature of the circuit is maintained by the network. The circuit may either be a fixed one that is always present, or it may be a circuit that is created on an as-needed basis. Even if many potential paths through intermediate devices may exist between the two devices communicating, only one will be used for any given dialog. This is illustrated in Figure 1.
The classic example of a circuit-switched network is the telephone system. When you call someone and they answer, you establish a circuit connection and can pass data between you, in a steady stream if desired. That circuit functions the same way regardless of how many intermediate devices are used to carry your voice. You use it for as long as you need it, and then terminate the circuit. The next time you call, you get a new circuit, which may (probably will) use different hardware than the first circuit did, depending on what's available at that time in the network.
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