In this chapter
Our exploration of networking has, so far, centered primarily on the local area network (LAN). LANs, howevereven the largestare isolated; they can only connect computers and other devices in a fairly small geographical area. Large companies and institutions that span multiple sites need to be able to connect all their LANs into one large network. Wide area networks (WANs) are networks made up of a number of LANs. So, a wide area network can be defined as a collection of LANs that extend over a wide geographic area.
To connect LANs at different locations, some sort of technology must be used that can move data across great distances but still have it arrive at its final destination intact. A number of different technologies exist that can be used to move data from physical site to physical site.
This chapter will concentrate on the different WAN technologies that are in use today. Many of these technologies make use of the Plain Old Telephone System or POTS . The use of VPNs or Virtual Private Networks is a way to take advantage of the infrastructure supplied by the Internet. Secure private connections can be made between networks over the public Internet. We will discuss VPNs in Chapter 17, "Networking on the Run." In this chapter we concentrate on technologies that are used by larger companies and institutions (although they don't have to be huge companies; they just have to be able to afford the technology). WAN technologies have actually been around since the days of the mainframe.