A Wide Area Network (WAN) is a network that spans a large geographical area, the most common example being the Internet. This is contrasted to smaller local area networks (LANs) and metropolitan area networks (MANs). LANs are home or office networks, while a MAN might encompass a campus or service residents of a city, such as in a citywide wireless or WiFi network.
The Internet is a public WAN, but there are many ways to create a business model or private version. A private network is essentially two or more LANs connected to each other. For example, a company with offices in Los Angeles, Texas and New York might have a LAN setup at each office. Through leased telephone lines, all three LANs can communicate with each other, forming a WAN.
Routers are used to direct communications between LANs communicating on a WAN. The router, installed on the leased line, reads the "envelopes" or headers on each packet of data that passes through the WAN, sending it to the proper LAN. When the packet arrives at the LAN, a device called a switch sends the data packet on to the correct machine. Hence, the WAN acts like an interface between LANs for long-distance communication. One that runs on a leased line is private, as there is no public traffic on the line.
Because leased lines are expensive, many businesses that require a WAN use an Internet Service Provider (ISP) to provide access instead. In this case, each LAN in the WAN communicates through a standard digital subscriber line (DSL) account. The DSL Internet account uses an existing telephone line while sharing that line with the telephone.
A DSL-based WAN uses public Internet lines. To protect it from intrusion, a Virtual Private Network (VPN) is set up. Using a VPN, all traffic remains encrypted en-route through the Internet, and is decrypted only at its destination. This is referred to as "tunneling," because the WAN is creating a secure channel through a public space. Firewalls also block intrusion by hackers. This type of is arguably the most popular because it is cost-efficient with great benefits. It operates at high transfer speeds and is an "always on" connection, providing 24/7 uptime for the WAN.
The least expensive type of WAN uses the Internet over a dial-up modem. This is not as popular, since the price of DSL has decreased enough to become competitive with dial-up accounts. A dial-up modem only operates at 56 kilobits per second (kbps), while a standard DSL connection is about 20 times faster. A dial-up connection also cannot share telephone service. Finally, dial-up is not an "always on" connection. When offices are in different time zones, this can effectively reduce uptime.
A WAN is an excellent way for companies to utilize geographically remote resources and centralize productivity. A leased line or affordable DSL-based network allows employees, field personal, and management full or restricted access to pertinent data 24 hours a day, seven days a week. Considering the negligible cost of DSL today, it often makes good business sense.