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A computer network, often simply referred to as a network, is a group of computers and network devices connected by any communications channels that facilitates communications among users and allows users to share resources with other users within that connected environment.
The Advanced Research Projects Agency (ARPA) funded the design of the Advanced Research Projects Agency Network (ARPANET) for the United States Department of Defense. It was the first operational and the world's first packet switching networkin the world.Development of the network began in 1969, based on designs developed during the 1960s.
What is OSI Model & why it is important ?
The Open System Interconnection (OSI) reference model describes how information from a software application in one computer moves through a network medium to a software application in another computer. The OSI reference model is a conceptual model composed of seven layers, each specifying particular network functions. The model was developed by the International Organization for Standardization (ISO) in 1984, and it is now considered the primary architectural model for intercomputer communications. The OSI model divides the tasks involved with moving information between networked computers into seven smaller, more manageable task groups. A task or group of tasks is then assigned to each of the seven OSI layers. Each layer is reasonably self-contained so that the tasks assigned to each layer can be implemented independently. This enables the solutions offered by one layer to be updated without adversely affecting the other layers. The following list details the seven layers of the Open System Interconnection (OSI) reference model:
An easy way to remember the seven layers is the sentence "All people seem to need data processing."
- All Application layer
- People Presentation layer
- Seem Session layer
- To Transport layer
- Need Network layer
- Data Data link layer
- Processing Physical layer
The OSI reference model can be divided into two categories
- upper layers
- lower layers.
User can interact with upper layer (Application Layer only).IT deal with application issues and generally are implemented only in software. Both users and application layer processes interact with software applications that contain a communications component. The term upper layer is sometimes used to refer to any layer above another layer in the OSI model.
The lower layers of the OSI model handle data transport issues. The physical layer and the data link layer are implemented in hardware and software. The lowest layer, the physical layer, is closest to the physical network medium (the network cabling, for example) and is responsible for actually placing information on the medium.
- Personal area network
- Local area network
- Home area network
- Campus network
- Metropolitan area network
- Wide area network
- Global area network
- Enterprise Private Network
- Virtual private network
- Internetwork
- Internet
- Intranets and extranets
- Overlay Network
