Wednesday, 5 October 2011

Computer Network: 
A Computer network is simply two computers that communicate with each other. Even through networks are usually consist of more then two computers but still the principles of network communication are the same for two, three or even thousands computer. 
Networks usually fail into one of the two groups local area network and Wide Area Network. A LAN connects computers located near each other. In some case "local" means within the same room or building. In other case "local" refers to computers located several miles apart. In contrast WAN consist of computers in different cities, states or even countries. You can refer to WAN as long-haul networks because of the great distance the information they exchange must travel. 
Communication in computers: 
Conceptually computers use a language to communicate and all languages consist of the same basic components letters and symbols, which combine to form words or ideas. 
Similarly, computers use a language composed of binary digits that represents either 0 or 1 Computer combine 1's or 0's to form bytes of data (words) computers transmit multiple byte combinations to communicate meaningful information. 
Type of data transfer: 
When computers communicate with other devices computers transfer data in parallel or in a serial format. Most PCs use parallel communication for transforming data to their printers. Parallel communication simply means you simultaneously transfers data across multiple lines or wires. To send a byte of data all eight bits are send over each wires at same time 
In contrast serial data transfer occurs over one wire , one bit at a time. Normally networks use serial communication to transfer data from one computer to the next. serial communication requires bits of data to line up behind each other. 
Computers use different methods to transfer data over wires. You should understand three important terms that network professionals commonly use to describe these methods of transfer 
Half- Duplex 
Full-Duplex communication 
Simplex Occurs when data flow in one direction only (TV) Half-Duplex communication let data flow in two directions, but one direction at one time (Wireless) Full-Duplex communication lets data flow in both direction simulaneously (Telephone) 
Communication Switching: 
To perform data transfers, networks use communication switching. Communication switching lets hardware devices share physical lines of communications. To understand communication switching considers telephone communications. 

Circuit switching: 
Circuit switching creates a single unbroken path between two devices that want to communicate, While these two devices talk no other device can use this path. However when the two devices finishing talking they release the communication paths so that other devices can use it. In other words circuit switching lets devices share lines of communication but each device must wait for its turn. 
Packet switching: 
Most modern networks including the internet use packet switching. In –fact , you can refer to the internet as packet switching network. In a packet switched network , programs break data into pieces called packets and transmit them between computers. It’s not at all necessary for packets of some program to follow the same4 path. They can reach the destination through different paths and order of arrival can also be different. But in the end everything is arranged properly and restored at destination.


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