There are legions of people who, if asked to define a wide area network (WAN), just couldn’t do it. Yet most of them use the big dog of all WANs—the Internet—every day With that in mind, you can imagine that WAN networks are what we use to span large geographic areas and truly go the distance. Like the Internet, WANs usually employ both routers and public links, so that’s generally the criteria used to define them.

Here’s a list of some of the important ways that WANs are different from LANs:

• WANs usually need a router port or ports.
• WANs span larger geographic areas and/or can link disparate locations.
• WANs are usually slower.
• We can choose when and how long we connect to a WAN. A LAN is all or nothing— our workstation is connected to it either permanently or not at all, although most of us have dedicated WAN links now.
• WANs can utilize either private or public data transport media such as phone lines.

We get the word Internet from the term internetwork . An internetwork is a type of LAN and/or WAN that connects a bunch of networks, or intranets . In an internetwork, hosts still use hardware addresses to communicate with other hosts on the LAN. However, they use logical addresses (IP addresses) to communicate with hosts on a different LAN (other side of the router).

And routers are the devices that make this possible. Each connection into a router is a different logical network. Figure 1.5 demonstrates how routers are employed to create an internetwork and how they enable our LANs to access WAN resources.

The Internet is a prime example of what’s known as a distributed WAN—an internetwork that’s made up of a lot of interconnected computers located in a lot of different places. There’s another kind of WAN, referred to as centralized, that’s composed of a main, centrally located computer or location that remote computers and devices can connect to.