Computer Network
Computer network
What is a Network ?
At home, your computer might be connected to its own printer and scanner. This works well as you are the only person who will be using them. But you must have noticed that much of the time, though, they probably are being used and just lie idle.
But at places where many computers are used such as your school or offices or banks etc., it would cost a lot of money for every computer to have its own printer. And for the majority time, like your printer at home, it would not be used.
But by joining computers together to form a network, they are able to share one printer. This means that more money can be spent buying a better quality printer and that the printer is being used much more of the time. Now this one computer can shared among a number of computers if they are interconnected. Interconnected computers form the computer network.
As well as sharing hardware, a network allows computers or users to share software and data. In the following lines you are going to learn more about networks and networking.
NOTE
A computer that is not connected to a network is known as a Stand-alone Computer.
A computer connected to a network is known as A Workstation or A Node or A Host.
Networking
Networking, in general refers to the creation of networks. Network is a group of devices linked to one another. For example, network of telephones, or radio network or cable network etc. So, networking makes sharing of information and resources easier. Same way, if we interconnect computers, it will form a network of computers.
Need for Networking -
The need for networking can be summarized in these lines; the networking is needed because :
1. It breaks the barriers of distance, cost and time.
2. It is very cost effective as compared to telephone networks.
3. All types of data viz. text, audio, video, pictures, graphics etc. can be transmitted through it.
Components of a Computer Network
Since a network refers to interlinked devices, a computer network means interlinked computers. Computers can be interlinked directly with the help of cables. In such as network, there would be three components playing their roles
i) the sender computer
i) the communication channel
iii) the receiver computer.
Computers can also be connected vla telephone so that telephone lines can work as communication channel for them. When computers are connected via telephones, as additional equipment called modem is used. This is because the data signal generated by computers (digital signal) is in a form which is different from the signal form that can be carried by telephone lines (analog signal). The modem converts the computer generated signal (digital signal) into a form that can be carried by telephone cables (analog signal).
In computer network there are five components playing these roles:
1. Sender computer
2. Sender equipment (modem)
3. Communication channel (telephone cables)
4. Receiver equipment (modem
5. Receiver computer.
By communication channels the connecting cables are being talked about. The cables that connect two or more workstations are the communication channels.
In LAN (Local Area Networks i.e, very small networks) many different types of media are use. Twisted pair, coaxial cable are by far the most common. Most recently, very serious consideration has been given to the use of optical fibre technology in LANS. Other media e.g., microwave transmission, infrared, telephone line etc. are also used figure 5.2 shows twisted pair and coaxial cables.
Modem
Modem is short name for Modulator-DEModulator where Modulator can convert digital signals to analog signal and Demodulator does the opposite. Modems transmit data at different speeds, measured by the number of bits of data they send per second (bps). Examples of Modem speeds for : 256 kbps, 512 kbps, 2 Mbps, 8 Mbps etc.
Types of Networks
Local Area Network (LAN)
Small computer networks that are confined to a localised area (e.g., an office, a building or factory) are known as Local Area Network (LAN). The key purpose of a LAN is to serve its users in resource sharing. The hardware as well as software resources are shared through LANS. For instance, LAN users can share data. Information, programs, printer, hard-disks, modems etc.
Local Area Networks implement technology. that all the devices attached the LAN share a single communications medium, usually a coaxial, twisted- pair, or fiber-optic cable.
A physical connection to the network is made by putting a network interface card (NIC) inside the computer and connecting it to the network cable. Once the physical connection is in place, the network software manages communications between stations on the network.
To send messages to and from computers, the network software puts the message information in a packet. (If the message to be sent is too big to fit into one packet, it will be sent in a series of packets.) In addition to the message data, the packet contains a header and a trailer that carry special information to the destination. One piece of information in the header is the address of the destination.
The NIC transits the packet onto the LAN as a stream of data represented by changes in electrical signals. As it travels along the shared cable. Each NIC checks its destination address to determine if the packet is addressed to it. When the packet arrives at the proper address, the NIC copies it and gives its data to the computer. Since each individual packet is small, it takes very little time to travel to the ends of the cable. After a packet carrying one message passes along the cable, another station can send its packet. In this way, many devices can share the same LAN medium.
The following characteristics differentiate one LAN from another:
1. Topology The geometric arrangement of devices on the network. For example, devices can be arranged in a star, a ring or in a straight line.
2. Protocols The rules and encoding specifications for transferring data. The protocols also determine whether the network uses a peer-to-peer or client/ server architectu
3. Media Devices can be connected by twisted-pair wire, coaxial cables or fiber optic cables. Some networks (wireless) to without connecting media altogether, instead communicating via radio waves. 
Metropolitan Area Network (MAN)
Metropolitan Area Networks are the networks spread over a city. For example, cable TV networks that are spread over a city, can be termed as metropolitan area networks. The purpose of a MAN is the sharing of hardware and software resources among its users.
Wide Area Networks (WAN)
The networks spread across countries are known as WANS. A Wide Area Network (WAN) I5 a group of computers that are separated by large distances and tied together. It can even be a group of LANS that are spread across several locations and connected together to look like big LAN.
Computers connected to a wide-area network 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. Wide area networks (WANs) combine the continuous error detection and correction techniques Included In synchronous communications with robust network problem determination and data routing to form powerful backbones ensure high-quality, relable service for end users. These networks allow multiple users to access a variety of host computers simultaneously through the same physical medium, while separating each user's session so that no user is aware of another on the network. Wide area networks also operate at speeds much higher than the 19,200- bps limit of normal voice-grade telephone lines.
It is possible to enter data for sales and transactions at the point-of-sale terminals using WANs.
It is also possible to centralize this data in a computer for processing or reporting purposes. For example, Supermarkets in advanced countries connected through WANs can send all sales data from their remote sale centers and the central purchase and distribution center can monitor all the sale fligures on a day-to-day basis.
0 टिप्पणियाँ