Wednesday, March 28, 2012

TYPES OF NETWORK:


A network consists of two or more computers that are linked in order to share resources (such as printers and CD-ROMs), exchange files, or allow electronic communications. The computers on a network may be linked through cables, telephone lines, radio waves, satellites, or infrared light beams.

A computer network, often simply referred to as a network, is a collection of computers and devices interconnected by communications channels that facilitate communications and allows sharing of resources and information among interconnected devices. Computer networking or Data communications (Datacom) is the engineering discipline concerned with the computer networks..

A group of computers and other devices connected together is called Network, and the concept of connected computers sharing resources is called Netwoking.

Types of Networks
In general, all networks have certain components, functions and features in common. These include servers, clients, media, shared data, shared printers, resources etc. And, the type of network depends on numerous factors like;
         Size of the organization
         Level of security required
         Type of business
         Level of administrative support available
         Needs of the network users
         Network budget

Depending on above factors, networks can be divided into two broad categories 1) peer-to peer and 2) Server-based networks.

Peer-to-Peer Networks
In a peer-to-peer network, there are no dedicated servers or hierarchy among the computers .All the computers are equal and, therefore, are known as peers. Normally, each computer functions as both a client and a server, and there is no one assigned to be an administrator responsibility for the entire network. The user at each computer determines what data on their computer gets shared on the network. Peer-to-peer networking is built into the operation system such as Microsoft Windows 95, 98, and XP. No additional software is required to setup a peer-to-peer network.

Peer-to-peer network is appropriate where
         There are fewer than 10 users
         The users are all located in the same general area
         Security is not an issue
         The organization and the network will have limited growth within the foreseeable future.

Server-based Network
In an environment with more than 10 users, a peer-to-peer network with computers acting as both servers and clients may not be adequate. Therefore, most networks have dedicated servers. A dedicated server is one that only functions as a server and is not used as a client or workstation. Servers are dedicated because they are optimized to quickly service requests from network clients and ensure the security of files and directories. Server-based networks have become the standard model for networking.

The variety of tasks that servers perform is varied and complex. Servers for large networks have become specialized to accommodate the expanding needs of users. 

The different types of servers include;
Ø File and print servers
Ø Application servers
Ø Mail servers
Ø Fax servers
Ø Communication servers
Ø Web servers etc.

A server-based model has following advantages
Ø Sharing resources: Server-based sharing of data can be centrally administered and controlled.
Ø Security: Security is most often the primary reason for choosing a server-based approach to networking. In a server-based environment security can be managed by one administrator who sets the policy and applies it to every user on the network.
Ø Backup: It is easier to make sure that the data is backed up on a regular schedule, at one place.
Ø Centralized administration of resources.
Ø Avoiding redundancy of data
Ø Network resources can be maintained very easily.

The three types of networks are: the Internet, the intranet, and the extranet. Examples of different network methods are:
  • Local area network (LAN), which is usually a small network constrained to a small geographic area. An example of a LAN would be a computer network within a building.
  • Metropolitan area network (MAN), which is used for medium size area. examples for a city or a state.
  • Wide area network (WAN) that is usually a larger network that covers a large geographic area.
  • Wireless LANs and WANs (WLAN & WWAN) are the wireless equivalent of the LAN and WAN.
  • SAN - Storage Area Network, System Area Network, Server Area Network, or sometimes Small Area Network
  • CAN - Campus Area Network, Controller Area Network, or sometimes Cluster Area Network
  • PAN - Personal Area Network
  • DAN - Desk Area Network
PERSONAL AREA NETWORK (PAN)
A Personal Area Network (PAN) is a computer network used for communication among computer and different information technological devices close to one person. Some examples of devices that are used in a PAN are personal computers, printers, fax machines, telephones, PDAs, scanners, and even video game consoles. A PAN may include wired and wireless devices. The reach of a PAN typically extends to 10 meters. A wired PAN is usually constructed with USB and Firewire connections while technologies such as Bluetooth and infrared communication typically form a wireless PAN.

Local Area Network (LAN)
A network is said to be Local Area Network (LAN) if it is confined relatively to a small area. It is generally limited to a building or a geographical area, expanding not more than a mile apart to other computers. However, one LAN can be connected to other LANs over any distance via telephone lines and radio waves.

A system of LANs connected in this way is called a wide-area network (WAN). Each node (individual computer ) in a LAN has its own CPU with which it executes programs, but it also is able to access data and devices anywhere on the LAN. This means that many users can share expensive devices, such as laser printers, as well as data. Users can also use the LAN to communicate with each other, by sending      e-mail or engaging in chat sessions.
  
LAN configurations consist of:

·         A file server - stores all of the software that controls the network, as well as the software that can be shared by the computers attached to the network.

·         A workstation - computers connected to the file server (Mac or PCs). These are less powerful than the file server

·         Cables  - used to connect the network interface cards in each computer.

LANs are capable of transmitting data at very fast rates, much faster than data can be transmitted over a telephone line; but the distances are limited, and there is also a limit on the number of computers that can be attached to a single LAN.

Advantages of Local Area Network (LAN);
Ø File sharing: A LAN enables many users to share a single copy of a file stored on a central file server. This helps the organization in keeping its records, documents and other files consistent.

Ø Transfer Files: A LAN enables to copy files from one machine to another without having to exchange floppy diskettes.

Ø Sharing of computer hardware: using LAN, share one or more hardware such as printer, modem, fax machine among several computers.

Ø Sharing of computer software: A LAN enables people to use the same copy of software. The LAN administrator can install software updates.

Ø Communication: LAN can be used to send letters, reports, messages to other people in other parts of the building and it provides a paperless office.

METROPOLITAN AREA NETWORK ( MAN):
MAN are large computer networks usually spanning a city. They typically use wireless infrastructure or Optical fiber connections to link their sites .A MAN is optimized for a larger geographical area than a LAN, ranging from several blocks of buildings to entire cities. MANs can also depend on communications channels of moderate-to-high data rates. A MAN might be owned and operated by a single organization, but it usually will be used by many individuals and organizations. MANs might also be owned and operated as public utilities. They will often provide means for internetworking of local networks. Metropolitan area networks can span up to 50km, devices used are modem and wire/cable.

WILD AREA NETWORK (WAN):
A computer network that spans a relatively large geographical area. Typically, a WAN consists of two or more local-area networks (LANs). Computers connected to a wide-area network are often connected through public networks, such as the telephone system. They can also be connected through leased lines or satellites. The largest WAN in existence is the Internet.

A network device called a router connects LANs to a WAN. In IP networking, the router maintains both a LAN address and a WAN address.

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.

Ø  Speed. Sharing and transferring files within Networks are very rapid. Thus saving time, while maintaining the integrity of the file.
Ø  Cost. Individually licensed copies of many popular software programs can be costly. Networkable versions are available at considerable savings.
Ø  Security. Sensitive files and programs on a network are passwords protected, so that you do not have to worry about illegal copying of programs.
Ø  Centralized Software Management.  Software can be loaded on one computer (the file server) eliminating that need to spend time and energy installing updates and tracking files on independent computers throughout the building. 
Ø  Resource Sharing. Resources such as, printers, fax machines and modems can be shared. 
Ø  Electronic Mail. E-mail aids in personal and professional communication. Electronic mail on a LAN can enable staff to communicate within the building having tot to leave their desk. 
Ø  Flexible Access. Access their files from computers throughout the firm. 
Ø  Workgroup Computing. Workgroup software (such as Microsoft BackOffice) allows many users to work on a document or project concurrently.

Ø  Server faults stop applications being available
Ø  Network faults can cause loss of data.
Ø  Network fault could lead to loss of resources
Ø  User work dependent upon network
Ø  System open to hackers
Ø  Decisions tend to become centralised
Ø  Could become inefficient
Ø  Could degrade in performance
Ø  Resources could be located too far from users
                                                

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