WAN, stands for Wide Area Network. It is different from LAN, or local are network, in that it covers a “wide area” instead of just the local area. A local area being a core of a town, or a headquarters building, for example, and a wide area being a remote site across the street, or miles away. At the remote site, there is usually a LAN, that is local to that site. A picture of LANs and WANs is below:
In the above picture the lighting bolt represents the WAN. In this scenario it is connecting a router from one site to a router at another site. These are point to point WANs. An example of a technology that would be used here is T1 or a frame relay. T1 speeds are 1.544 Mpbs and utilize a serial interface on a router. Frame Relay speeds are variable. Some range from 56kbps up to 45Mbps.
Another characteristic of WANs it is it involves using a Service Provider from point A to point B, and involves handing off the network to that Service Provider at a dmarc, or demarcation point. The demarcation point indicates points of responsibility for the customer and for the Service Provider. So, to break down that configuration, there exists a router, a serial interface cabled to a csu/dsu, (channel service unit/data service unit) which is the handoff point, or demacation point, then the Service provider takes it from there, and is responsible for maintenance of the hardware and network at that point to the corresponding csu/dsu at the remote site. See below:
Some networks use T1s at 1.544Mbps, which is a point to point network. Some networks use a T3, also point to point, which is 45Mbps. It depends on the bandwidth requirements and what the budget is. Another WAN type is frame relay, which is a packet switched network that runs over a T1 or T3. Some other WAN Types are dsl digital subscriber line, which varies from 1 Mbps to 400Mbps download speeds , and isdn, or integrated services digital network at 144kbps or 192 kbps. Newer networks use everything from fiber optic cable to internet with vpn. Some other examples of WANS are ATM or asynchronous transfer mode, cable modem, dial-up internet, and leased line.
Ken Hagen CCIE #56460 