Chapter 13. Expanding a LAN with WAN Technology

In this chapter

• Defining the wide area network

• WAN technology and the Plain Old Telephone System

• Working with asynchronous and synchronous modems

• Understanding the T-carrier system

• Differentiating between circuit- and packet-switching WAN technologies

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.

Note

You might be wondering what the difference is between an internetwork and a WAN. An internetwork is a network of networks, but it doesn't necessarily span large geographical areas. An internetwork can exist at one site of a large company and is more about ways of expanding a LAN or LANs and still conserving network bandwidth or getting different network architectures to talk to each other on the same network. A WAN is a network that makes use of some of the same devices as an internetwork, but it exists primarily because of the need to connect LANs at different physical locations.