WIDE AREA NETWORK

WANs are built to provide communication solutions for organizations or people who need to exchange digital information between two distant places (in one country or in two different countries). Since the distance is long, the local telecommunication company is involved, in fact, WANs are usually maintained by the country’s public telecommunication companies (PTT’s – like AT&T, Sprint, BEZEQ), which offer different communication services to the population.
The main purpose of a WAN is to provide reliable, fast and safe communication between two or more places (Nodes) with low delays and at low prices. WANs enable an organization to have one integral network between all its departments and offices, even if they are not all in the same building or city, providing communication between the organization and the rest of the world. In principle, this task is accomplished by connecting the organization (and all the other organizations) to the network nodes by different types of communication strategies and applications. Since WANs are usually developed by the PTT of each country, their development is influenced by each PTT’s own strategies and politics.
Basic WANs
The basic WAN service which the PTT usually offers (for many years) is a Leased Line. A Leased Line is a point-to-point connection between two places, implemented by different transmission media (usually through PSTN Trunks), which creates one link between its nodes. An organization whose networks are based on such lines has to connect each office with one line, meaning that each office is connected to as many lines as the number of offices it is connected to, as shown in the figure below.
In the past, leased lines were just 4 wires connected between the two places, and the responsibility for communication fell on the organization and the good will of the PTT’s personnel. These lines were not managed and often suffered from a lot of noise. Moreover, these lines consumed the PTT’s bandwidth even when no transmission was occurring. Today, leased lines are usually point-to-point digital lines, which are implemented by creating a permanent channel, with known bandwidth, between the two nodes and transferring the data by a dedicated digital network, which enables automatic management on the line and minimizes noise interference.
For ages, the communication strategies of organizations were based on those lines and were usually built in a star configuration in order to minimize the amount of lines needed. It’s easy to see that this configuration has a very weak point at its center.
In the 1970′s, some PTTs built digital circuit switched communication networks which enabled creating a non permanent digital connection between two places (like telephone), but those networks did not provide the breakthrough in the communication technologies.
Packet Switched WANs
The Packet Switched WAN appeared in the 1960′s, and defined the basis for all communication networks today. The principle in Packet Switched Data Network (PSDN) is that the data between the nodes is transferred in small packets. This principle enables the PSDN to allow one node to be connected to more than one other node through one physical connection. That way, a fully connected network, between several nodes, can be obtained by connecting each node to one physical link, as shown in the figure below.
Another advantage for Packet Switching was the efficient use of resources by sharing the Network bandwidth among the users (instead of dividing).
Today, X.25 transfer rates are considered to be very low, and this service is expected to be replaced with new services by the end of the century.
New Technologies
The communication target today is the ATM (and B-ISDN services). However, until applications and technologies for ATM become more developed, two main mid-time services are popularly used in the world today.
The first service is Frame Relay, which is considered to be the next generation for X.25, and enables faster communication rate (up to T3/E3) and better communication protocol. Until all its standards will be completed, Frame Relay is mainly a point-to-point service and replaces the leased lines. The second network service is ISDN, which is a fully digitized service, enabling communication for most types of data (voice, computer data and images) at all the network nodes (meaning in every house). This service is at its peak today and is been implemented mostly in Europe.
Those two communication networks are not fully developed yet, and will be spread in the world in the next years.
Future WANs
The ATM network and B-ISDN services, which provide solutions for all types of data (including video) are been developed today and are beginning to be implemented.
But even today, new networks are been designed for future demands. Those new networks are aimed to work at enormous rates of Giga-bps, and are providing new challenges for their designers.
For example in a medium speed of 64Kbps, transferring a file of 10KBit over a distance of 3000Km will take 0.015625sec plus a minimum of 10 microseconds is needed for light to reach from 1 point to the other. In a Giga-Net of speed 10E+10bps, transferring that same file will take 1 microsecond (plus 10 microseconds for light), meaning that the file will reach the network before the first bit will reach its destination. This example, and other issues make the next generation of WANs a very challenging one.
The WAN, has come a long way since the days of analog leased lines and is taking more and more tasks from the old separated networks into one integral network which enables good communication for any type of data or application.