How does a Wide Area Network work?
A Wide Area Network (WAN), as its name indicates, is designed to enable computer users to communicate and collaborate over a wide geographic area.
Today, WANs are most often used by multi-site businesses to interconnect Local Area Networks (LANs) at offices in various locations. The aim is to emulate a single private network that links all users irrespective of where they are located.
The users can be in different cities, regions and even countries. Indeed, the Internet can be thought of as a very large WAN that connects every Internet user in the world.
As well as data traffic, WANs can be used to carry voice and video traffic. Indeed, before the Internet era, WANs were first used for voice traffic. A Wide Area Network allows an organisation to route internal telephone calls made between geographically remote offices over the WAN instead of using the public-switched telephone network.
In a large organisation, this intra-company traffic can make up a significant part of total voice traffic, and in the days when long-distance calls were expensive, the cost savings were considerable.
WANs are still used for voice traffic, but the biggest benefits these days come from using this technology to carry intra-company data and video traffic.
By routing LAN traffic, internal telephone calls and inter-site videoconferencing over the WAN, large organisations can reduce their dependence on public telecommunications services and so rationalise their telecoms operating expenditure (Opex).
Wide Area Network connectivity has often been provided by leased lines. These are dedicated point-to-point connections made of fibre optic (or copper) cables that physically link two sites and are separated from general public telecommunications networks.
At each end of the leased line, a router connects the LAN on one side with a second router within the LAN on the other. Leased lines have historically been relatively expensive, so their use was limited to large corporations.
But the cost has dropped considerably in the past decade and businesses can now buy leased line services offering a wide variety of speeds up to 1 gigabit/s.
As well as leased lines, WANs can be created using a variety of methods and technologies that leverage the public network infrastructure and so are more economical.
The oldest WAN protocol, X.25, was once highly popular but has been superseded by faster, more advanced WAN technologies, including Frame Relay, MPLS, ATM and packet over Sonet/SDH.
Virtual Private LAN Services (VPLS) is one of the newest and most interesting WAN services. It allows users in geographically dispersed sites to appear to be connected to a single "virtual" private network.
In much the same way that a bridge or switch is often used to join two distinct physical networks inside an office to create one LAN, VPLS emulates a switch or bridge that can combine geographically remote LANs into a single Ethernet network.
VPLS is simpler and more cost effective than other services that have traditionally been used to link geographically dispersed Ethernet Networks together.
It enables business to connect all of their sites together so that, as far as applications and users are concerned, everyone appears to be attached to the same network.