The Sustainable Network

Just a Few More Terms: Hosts, Routers, Switches, LANs, and WANs

At the heart of the network lies a mesh of interconnected routers and switches, each capable of processing and forwarding millions of packets (think bite-size packages of bits and bytes) per second. These network devices operate the same way as all the handlers in the postal system. Your letter goes in steps to intermediate points, and workers at each intermediate point forward it on to the next point, which takes it closer and closer to its end destination. Network devices do the same thing. They are the traffic handlers in the middle of the country in Figure 2-1 and Figure 2-2, and they are the means by which the network finds you among the billion-and-a-half network users across the world.

At the most fundamental level, routers and switches are responsible for making sure traffic packets get from point A to point B on the network, by reading the header information and passing the packets on. The differences between routers and switches are starting to blur, as functionality converges and network layers collapse, but in simple terms, they're distinguished by the types of information they evaluate when making their decisions on how to transport the traffic.

A switch on your local network typically keeps track of the host that's connecting to the Internet. The switch that is physically closest to you may be downtown at the DSL center or at the end of your roaming wireless connection. But when you connect to the network, ...