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Network

Definition
A computer network is a group of computer systems and other computing hardware devices that are linked together through communication channels to facilitate communication and resource-sharing among a wide range of users.
Networks are used for the following key reasons:
1. To facilitate communication via email, video conferencing, instant messaging etc.
2. To enable multiple users to share a single hardware device like a printer or scanner.
3. To enable file sharing across the network.
4. To allow for the sharing of software or operating programs on remote systems.
5. To make information easier to access and maintain among network users.
Basic Elements of a Network
There are three basic components/Elements of Computer Network
1. Sender: Creates and sends a message
2. Medium: Carriers a message.
This is a communication stream through which the data is being transmitted. 
For example – Cable media or wireless media.
3. Receiver: Receives a message
Types of computer network
A network can be characterized by its physical capacity or its organizational purpose. Following are basic types of computer network
1. LAN
2. MAN
3. WAN
4. Value-added network
1. LAN
A local area network (LAN) is a computer network within a small geographical area such as a home, school, computer laboratory, office building or group of buildings.  Each computer or device on the network is a node.
E.g. Computer connected with each other in computer Lab.
Functions of LAN
LAN’s main function is to provide resource sharing and mutual communication, which provides the following main services:
1. The sharing of resources:  including hardware resource sharing, file sharing, and software inventory data sharing. Users can share a network system software and application software.
2. Data transfer and e-mail: Data and network file transfer is an important feature of modern LANs not only transmits files, data, information, but also can send voice, images.
3. Improve the reliability of the computer system: LAN computers can back each other, avoiding the stand-alone system without backup failure may occur when system failures, greatly improving the reliability of the system, particularly in the industrial process control, real-time data processing and other applications, is particularly important.
4. Easy to distributed processing: Use of network technology you can have more than one computer connected to a high-performance computer system (Server).
Features of LAN
1. Coverage area of LAN is few kilometers.
2. The communication quality is better in LAN, the transmission error rate are low as compare to WAN.
3. A LAN usually has low cost, installation, expansion and maintenance and LAN installation is relatively simple.
4. LAN supports a variety of communications transmission medium such as a cable (thin cable, thick cable, and twisted pair), fiber and wireless transmission.
5. In LAN user can run multiple devices to share a transmission medium.
6.  High throughput.
7. Full time connectivity to local services.
8. High speed data transfer rates ranges from 1Mbps to 100Mbps.
2. MAN
A Metropolitan Area Network is a network that connects two or more Local Area Networks or Campus Area Networks together but does not extend beyond the boundaries of the town/city. Routers, switches and hubs are connected to create a Metropolitan Area Network.
E.g. Different branches of college connected with each other within a city.
MANs are extremely efficient and provide fast communication via high-speed carriers, such as fiber optic cables.
There are three important features which discriminate MANs from LANs or WANs:
1. The network size falls intermediate between LANs and WANs. A MAN typically covers an area of between 5 and 50 km range.
2. A MAN (like a WAN) is not generally owned by a single organization. The MAN, its communications links and equipment are generally owned by either a consortium of users or by a network service provider who sells the service to the users.
3. A MAN often acts as a high speed network to allow sharing of regional resources. It is also frequently used to provide a shared connection to other networks using a link to a WAN.
3. WAN
Wide Area Network, WAN is a collection of computers and network resources connected via a network over a geographic area. It is a computer network that covers a far wider area than a LAN (Local Area Network). WANs cover cities, countries, continents and the whole world. 
Computers connected to a wide-area network are often connected through public networks, such as the telephone system.
E.g. Internet
Major characteristics/Features of WANs:
1. The data rates of WAN is low as compare to data transfer rate of local area network
2. WAN covers long span of area.
3. Cost effective, as compare to other means of communication over long distance.
4. WANs generally connect devices that are separated by a broader geographical area than can be served by a LAN.
5. WANs use the services of carriers, such as telephone companies, cable companies, satellite systems, and network providers.
6. WANs use serial connections of various types to provide access to bandwidth over large geographic area.
4. VALUE-ADDED NETWORK
A private network provider hired by a company to facilitate electronic data interchange (EDI) and/or provide other network services such as message encryption, secure email and management reporting.
A Value-Added Network (VAN) simplifies the communications process by reducing the number of parties with which a company needs to communicate. The VAN accomplishes this by acting as an intermediary between business partners that share standards based or proprietary data. VANs may be operated by large companies for efficient supply chain management with their suppliers, or by industry consortiums.
The use of VAN is reduced because of internet since it is much more cost-effective to move data over the internet than to pay the minimum monthly fees and per-character charges included in typical VAN contracts.
E.g. Easy Link provide value added network providing features such as real time delivery of documents, data security through high speed data transmission.
Features of Value added network
1. Provide encryption of data while its transmission.
2. Provide transfer of data in a specified format.
3. Real time delivery of data.
4. System Alerts – It has generated alerts confirming the receipt of delivery.
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