WAN is the acronym for, Wide Area Network and refers to a network used to connect different equipments from remote areas. This technology connects sites that are in diverse locations. Wide Area Networks (WANs) connect larger geographic area, such as New York, Canada, or the world. The geographical limit of WAN is unlimited. Dedicated transoceanic cabling or satellite uplinks may be used to connect this type of network. Hence, a WAN may be defined as a data communications network that covers a relatively broad geographic area to connect LANs together between different cities with the help of transmission facilities provided by common carriers, such as telephone companies. WAN technologies function at the lower three layers.
Normally, network services are provided by a Common Carrier of, for example, telephone company. Users can use services on rent basis. Available services include telephone network, leased line, packet switched network, X.25, ISDN, frame relay and cell relay.
WAN is composed of a number of autonomous computers that are distributed over a large geographical area. LAN can be extended across large distances using Satellite Bridge but still this cannot accommodate many computers arbitrarily. WAN must be scalable to long distances and many computers. Therefore, network must replace shared medium with packet switches to span long distances or many computers. Each switch moves an entire packet from one connection to another. This mechanism is called packet switching. These switches are nothing but a small computer with network interfaces, memory and program dedicated to packet switching function. These packet switches may connect to computers and to other packet switches, typically high-speed connections to other packet switches, lower speed to computers. These packet switches can be linked together to form WANs. WANs need not be symmetric or have regular connections, i.e. each switch may connect to one or more other switches and one or more computers.
Data delivery from one computer to another is accomplished through store and forward technology. Packet switch stores incoming packet and forwards the packet to another switch or computer that has internal memory. Therefore, this can hold a packet in queue if outgoing connection is busy.
• When a network spans a large distance or when the computers to be connected to each other are at widely separated locations a local area network cannot be used.
• A wide area network (WAN) must be installed. The communication between different users of “WAN” is established using leased telephone lines or satellite links and similar channels.
• It is cheaper and more efficient to use the phone network for the links.
• Most wide area networks are used for transferring large blocks of data between its users. As the data is from existing records or files, the exact time taken for this data transfer is not a critical parameter.
• Another example of WAN is an airline reservation system. Terminals are located all over the country through which the reservations can be made.
• It is important to note here that all the terminals use the same common data provided by the central reservation computer.
• Because of the large distances involved in the wide area networks, the propagation delays and variable signal travel times are major problems.
• Therefore most wide area networks are not used for time critical applications. They are more suitable for transfer of data from one user to the other which is not a time critical application. Wide area networks are basically packet switching networks.
• A WAN provides long distance transmission of data, voice image and video information over large geographical areas that may comprise a country, a continent or even the whole world.
• WAN contains a collection of machines used for running user (i.e. application) programs. All the machines called hosts are connected by a communication subnet.
• The function of the subnet is to carry messages from host to host. The subnet consists of two important components; transmission lines and switching elements.
• Transmission lines move bits from one machine to another. The switching elements are specialized computers used to connect two or more transmission lines. When data arrive on an incoming line, the switching element must choose an outgoing line to forward them.
• The switching elements are either called as packet switching nodes, intermediate systems, data switching exchanges or routers.
• When a packet is sent from one router to another via one or more intermediate routers, the packet is received at intermediate router. It is stored in the routers until the required output line is free and then forwarded. A subnet using this principle is called a point to point, store-forward or packet switched subnet.
• WAN’s may use public, leased or private communication devices, and can spread over a wide geographical area. A WAN that is wholly owned and used by a single company is often called as an enterprise network.
• In most WANs the network contains a large number of cables or telephone lines each one connecting a pair of routers.
• If two routers which are not connected to each other via a cable want to communicate, then they have to do it indirectly via other routers.
Packet switching technologies such as Asynchronous Transfer Mode (ATM), Frame Relay, Switched Multimegabit Data Service (SMDS), and X.25 are used to implement WAN along with statistical multiplexing to enable devices to share these circuits.
Packet switched subnet
• When a packet is sent from one router to the other, via some intermediate routers, the packet received at each intermediate router is stored until the required output line is free.
• Once the line becomes free, the packet is forwarded.
• A subnet working on this principle is called as point to point or store and forward or packet switched subnet.
• If the packets are small and of same size they are called as cells.
Router interconnection topologies
• Fig. shows some of the possible router interconnection topologies in a point to point subnet.
• The LANs have a symmetric topology while WANs have irregular topologies.
• The WAN s can also be formed using satellite or ground radio system. Satellite networks are inherently broadcast type so they are useful when the broadcast property is important.
Difference between WAN and LAN
With LAN additional expanses are rarely required once it is installed. With WAN, users must continue to pay a communication cost to their contracted common carrier.
- WAN is generally slower in transmission speed. Requesting the same level of speed as with LAN leads to a substantial increase in communication costs.
- The Satellite Bridge can extend LAN across large distances while in case of the WAN, it spans over a wide geographical area.
- LAN still can not accommodate arbitrarily many computers; WAN must be scalable to long distances and many computers.