A network that covers a broad area (i.e., any telecommunications network that links across metropolitan, regional, national or international boundaries) using leased telecommunication lines. Related terms for other types of networks are personal area networks (PANs), local area networks(LANs), campus area networks (CANs), or metropolitan area networks (MANs) which are usually limited to a room, building, campus or specific metropolitan area (e.g., a city) respectively. If you have a large campus network using routers and dynamic routing protocols and an internal infrastructure, you do not necessarily have a WAN. A wide area network (WAN) is a computer network that spans a relatively large geographical area. If your network uses a network infrastructure that is owned by your service provider, implementing WAN technologies, you have a WAN. Computers connected to a wide-area network are often connected through public networks, such as the telephone system.
The distinguishing features of a WAN:
Sending data long distances
Although distance is not a true criterion for determining whether your network is a WAN, most WANs do span a great distance, and the technologies used in the WAN depend a great deal on the distances involved. If your WAN spans only a single city, across town is a long way; nevertheless, your carrier may choose different technologies for that distance than they would if your network spanned a state, country, or continent. Although long distances are not criteria for defining a WAN, commonly, WANs do span substantial distances.
Implementing routing protocols
Routing protocols are also not true criteria for a WAN definition. A WAN can either use manual routing or implement a routing protocol such as RIP or EIRGP. Although larger, more complex networks like a national WAN may be easier to manage when implementing a routing protocol, their use does not dictate that you have a WAN. A large corporation could have a single (but large) building or a campus of several buildings that causes the network to have several routers. To make life easier on the routing front, you could choose to implement one of the many available routing protocols. So, although most WAN environments make use of routing protocols, not all networks that implement routing protocols are necessarily WANs.
Using carrier equipment
Means the equipment from your telephone company that allows you to connect your network to the backbone of its network. These network connections can be digital subscriber line (DSL), frame relay, fiber optic, broadband cable, or another technology used by your telephone company or network provider. This component really turns a network into a WAN, allowing your traffic to travel between your locations while traversing another provider’s network, mainly your ISP or telephone company. In some cases, this traffic may cross several providers’ networks. If you are connecting two offices and they are in different countries, you may be crossing networks owned by a regional provider, which connects to a national provider and then crosses borders and travels across the other national provider to another regional provider before finally reaching your other branch office location. It is this use of other people’s networks that really defines use of a large LAN versus a WAN (LANs are covered in the next section). So, a WAN is not related to the size of your network, or to your choice of routing protocols, or to any other factors.
However, in terms of the application of computer networking protocols and concepts, it may be best to view WANs as computer networking technologies used to transmit data over long distances, and between different LANs, MANs and other localised computer networking architectures. This distinction stems from the fact that common LAN technologies operating at Layer 1/2 (such as the forms of Ethernet or Wifi) are often geared towards physically localised networks, and thus cannot transmit data over tens, hundreds or even thousands of miles or kilometres. This could be to facilitate higher bandwidth applications, or provide better functionality for users in the CAN. A CAN, for example, may have a localised backbone of a WAN technology, which connects different LANs within a campus. The textbook definition of a WAN is a computer network spanning regions, countries, or even the world.