16.1 Network Infrastructure Concepts 
16.1.2 Wide Area Networks (WANs)
Organizations with multiple LANs in different geographical locations use WAN technologies to interconnect them. When the distance between LANs becomes too great, a Wide Area Network is needed. For instance an organization may have three locations, Phoenix, AZ, Denver, CO and Raleigh, NC. It is not realistic or cost effective for the organization to own all the cabling and equipment needed to interconnect these locations and a WAN connection is needed. The WAN's links or communication lines between locations can be dedicated or shared. These links are leased from a service provider such as the phone company and are not owned by the organization whose LANs are interconnected. WANs can be worldwide spanning thousands of miles.

Virtually every organization of any size today has a connection to the Internet. In its simplest form a WAN is created when a company connects its LAN to an Internet Service Provider (ISP). There may be 100 or more users on the LAN but there is only one WAN link to the ISP's network. Although a single LAN with an Internet connection is technically a WAN, the term is more often used to describe the links between two or more of an organization's LANs.

There are many WAN technologies that can connect LANs but the link is usually provided by a T1 (Trunk 1) connection or a fraction of a T1. A T1 connection provides 1.544 Mbps of bandwidth, which is considered a relatively low speed connection (compared to LANs) but it is usually adequate for Internet access or interconnecting multiple sites. The two most common WAN connection technologies are: dedicated T1 or shared Frame Relay. Others include Integrated Services Digital Network (ISDN) and Asynchronous Transfer Mode (ATM). Figure is a summary of WAN characteristics.

In most cases there is only one WAN link between locations, but it is possible to have more than one WAN link for redundancy or increased performance. If there are three locations, WAN links can be set up between each of the LANs (3 links) as shown in Figure . This will create multiple paths in case one of the links goes down.

Whether connecting to the Internet or connecting multiple corporate LANs, a networking device called a router is required. In order for an organization to connect to the Internet, a single router is needed. If an organization wants to connect two sites across a WAN link a router is needed at each location.