Types And Characteristics Of WANs Information Technology Essay

A Wan is a large area network that expands in a geographical area, such as a country or a continent. It is known also as a communication system that connects computer networks such as LANs (local area network) and MANs (metro area network). The connections go through local, national or international areas public or privately, using generally phones lines, referred to as POST, or employing PSTN (public switched telephone network) or fibre optics, creating the link between networks located in different facilities.

A WAN differs from a LAN in several important ways. Most WANs (like the Internet) are not owned by any one organization but rather exist under collective or distributed ownership and management. WANs tend to use technology like ATM, Frame Relay and X.25 for connectivity over the longer distances.

These networks contain a collection of machines to execute some programs which are called hosts. These are connected to networks that have communication through routers with each LAN and a WAN interface. Remote access is something vital for the companies and users because it allows you to have mobility and work through different areas. Also it gives the benefit to get better business out of your area.

Basically a WAN generates new applications viable, and some of them can cause important effects in whole society. In order to give some idea of important uses, some of them they are already commented before, we can see emphasize:

The access to remote programs.

The access to remote data bases.

Facilities of added value communication.

The principal components are routers, switches and modems. Devices on the subscriber premises are called customer premises equipment (CPE).

The subscriber owns the CPE or leases the CPE from the service provider. A copper or fibre cable connects the CPE to the service provider’s nearest exchange or central office.

This cabling is often called the local loop, or “last-mile”. Then Devices that put data on the local loop are called data circuit-terminating equipment, or data communications equipment (DCE). The customer devices that pass the data to the DCE are called data terminal equipment (DTE). The DCE primarily provides an interface for the DTE into the communication link on the WAN cloud.

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Types and characteristics of WANs:

The local area networks (LAN) are significantly different from the wide area network (WAN). The LAN’ sector is one of the fastest growths in the industry of the communications. The local area networks own the following characteristics.

Generally, the channels are property of the user or company. The connections are lines (from 1 Mbps to 200 Mbps). The DTEs is connected to the network via channels of low speed (from 600 bits to 56 Kbits). The DTEs are near to each other, generally in a same building. A DCE can be used to exchange between different configurations, but they are not as frequently as in the WAN.

The lines in LANs are better quality than the channels in the WAN, because to the differences between the local area networks and the wide network area, their topologies can take very different forms. The structure of the WAN tends to be more irregular, due to the necessity to connect many terminals, computers and switching centres.

Circuit Switching: The circuit switching is a WAN switching method which establishes, maintains and ends dedicated physical circuit through a carrying network for each session of communication. The switching circuit, which is used widely in the networks of the telephone companies, operates of form similar to one circuit, which is widely used in telephone company networks, operates similar to a normal telephone call. ISDN is an example of a circuit-switched WAN technology. Connections circuit switched one site to another are triggered when necessary and generally require low bandwidth band. The circuit switched connections are used primarily to connect remote users and mobile users to the corporate LAN. Also it is used as backup lines to circuit higher speeds, such as Frame Relay and other dedicated lines. One advantage is it is highly reliable for its function. A disadvantage is all the time spends to set up the channel and also there is the single point failure which can cause a disruption in communications.

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Message Switching: a computer is in charge to accept connected traffic of networks to him. The computer examines the direction that appears in the head of the message towards the DTE that must receive it. This technology allows recording the information to take care of it later. The user can erase, store, route or answer the message of automatic form.

Picture taken from technet.microsoft.com

Packet Switching: In this type of network the data of the users are disturbed in smaller pieces. These fragments or packages, you are inserted within information of the protocol and cross the network like independent organizations.

Connectionless and Connection-Oriented Services: they happen directly of the free situation to the way to transfer data. These networks do not offer confirmations, flow control and neither recovery of errors applicable to the entire network, although these functions if they exist for each particular connection. An example of this type of network is Internet.

In connection-Oriented packets switched, the multiplexing concept exists in channels and ports are known as virtual circuit or channel. The user pretends to have a dedicated resource, when he shares with another one then what it happens is that they take care of bursts of traffic of different users.

General routing issues

Congestion is about too much presence of packages in a part of one subnet. In cases of extreme congestion, routers start to reject packages, decreasing the system performance. The reasons of congestion are many, some of them are:

If in 4 lines, the information arrives to him at router and all needs the same line of exit, it exists competition.

Insufficient amount of memory in routers. But if you add more memory, this just helps until certain point because the time to arrive at first from the queue can be so long.

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Slow processors in routers. The analyse process of the packages are expensive, so slow processors can cause congestion. In that way the congestion propagates to the others routers…

The flow control and the control of congestion are not the same:

Flow control: is in charge of a fast emitter does not saturate to a slow receiver.

Control of Congestion: its function is to try to avoid that the network is overloaded. The solutions for the problem of congestion can be divided in two classes:

Open Loop: They try to solve the problem with a good design. They use algorithms to decide when to accept more packages, when to discard them, etc. But they do not use the actual situation of the network.

Closed Loop: The solution in this case is based on the feedback of the line. Generally they have three parts:

1. The system is monitored to detect when and where it happens the congestion.

2. This information goes towards where actions can be taken.

3. The operation parameters of the system adjust to correct the problems. Several measures of the performance can be used to measure the congestion.

The main measures used are: % of discarded packages, Queue length, Number of packages that “makes timed out” and/or relayed, the average delay of the packages.

3. Addressing and routing

It is necessary that any machine or host have one address, in order to get the information to the network. In the case of Internet, this are called IP address, and to each machine of the Network is assigned one. An IP address is a 32 bit number represented as four octets. Each of these four octets is in the range between 0 to 255.

Class A: a (8 bits red, 24 bits hosts)

Class B: a (16 bits red, 16 bits hosts)

Class C: a (24 bits red, 8 bits hosts)

Class D addresses are used for multicasting

Class E is for experimental purposes.

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