Wide Area Network (WAN)

A wide area network (WAN) is a telecommunications / computer network connecting computes that extends over a large geographical distance. WANs often connect multiple smaller networks, such as local area network (LANs) or metro area networks (MANs) Basically local area newtwork is subset of Wide area network (WAN). Most propular WAN in the world is Internet. Key technologies often found in WANs include SONET, Frame Relay, and ATM. Typically TCP/IP is the protocol used for a WAN in combination with devices such as routers, switches, firewalls and modems.

Example :
In the below diagram Chicago office is trying to connect Atlanta office. Onway both office can be connected by lay over fiber/copper wire from chicago to Atlanta . But in such scenario company has to invest lots of money by pacing fiber/copper wire and most of the company wouldn’t like to invest that much money . Also if number of office increae then situation is going to be complicated . To overcome such situation , Internet service provided (ISP) came in picture. Chicago office will be connected to local chicago ISP and similary Atlanta office will be connected to local Atlanta ISP. ISP will always have backbone to connect their offices. So all computes can be connected through ISP without any issue.

PC 1,PC2 and PC3 will be connected to internal switch in the Chicago office . Chicago office switch will be connected to wall Jack. From wall Jack to Chicago ISP company has to lay over wire/cable. Similarly PC 4,PC 5 and PC 6 will be connected to Atlanta ISP.Now all office can talk each other through ISP without any issue.
Chicago Office Computers <---> Switch <---> Wall Jack <---> Chicago ISP <---> Atlanta ISP <---> Wall Jack < ---> Switch <---> Atlanta Office Computes