What is computer network
A Computer Network or simply Network is a collection of computers and devices connected by communications channels that facilitates communications among users and allows users to share resources with other users.
Purpose of a Network:
- Facilitating communications. Using a network, people can communicate efficiently and easily via e-mail, instant messaging, chat rooms, telephony, video telephone calls, and videoconferencing.
- Sharing hardware. In a networked environment, each computer on a network can access and use hardware on the network. Suppose several personal computers on a network each require the use of a laser printer. If the personal computers and a laser printer are connected to a network, each user can then access the laser printer on the network, as they need it.
- Sharing files, data, and information. In a network environment, any authorized user can access data and information stored on other computers on the network. The capability of providing access to data and information on shared storage devices is an important feature of many networks.
- Sharing software. Users connected to a network can access application programs on the network.
A computer network allows sharing of resources and information among devices connected to the network. The benefits of networking computers and other devices include lower costs and increased productivity. With networks, resources can be shared, which results in less duplication and corruption of data.
Networks offer a quick and easy way to share files directly. Instead of using a disk or USB key to carry files from one computer or office to another, you can share files directly using a network.
Many popular software products are available for networks at a substantial savings in comparison to buying individually licensed copied for all of your computers. You can also load software on only the file server which saves time compared to installing and tracking files on independent computers. Upgrades are also easier because changes only have to be done once on the file server instead of on individual workstations.
All computers in the network can share resources such as printers, fax machines, modems, and scanners. Even outside of the internet, those on the network can communicate with each other via electronic mail over the network system. When connected to the internet, network users can communicate with people around the world via the network.
Networks allow their users to access files from computers throughout the network. This means that a user can begin work on a project on one computer and finish up on another. Multiple users can also collaborate on the same project through the network. Workgroup software like Microsoft BackOffice/Google Documents enables many users to contribute to a document concurrently. This allows for interactive teamwork.
Networks were categorized based on the Area, in past. Most of the times these differences were just limited to area the network is spanned over, although some of these could work on different technologies.
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 connections between devices. The reach of a PAN typically extends to 10 meters. Wired PAN network is usually constructed with USB and Firewire while wireless with Bluetooth and Infrared.
A local area network (LAN) is a network that connects computers and devices in a limited geographical area such as computer laboratory, office building, or closely positioned group of buildings. Each computer or device on the network could be a node.
A wide area network (WAN) is a computer network as term implies, covers a large geographic area such as a city, country, or spans even intercontinental distances, using a communications channel that combines many types of media such as telephone lines, cables, and air waves. A WAN is a geographically-dispersed collection of LANs. The Internet is the largest WAN, spanning the Earth.
A metropolitan area network (MAN) 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 immediate town/city. Routers, switches and hubs are connected to create a metropolitan area network.
A home area network (HAN) or home network is a residential local area network which is used for communication between digital devices typically deployed in the home, usually a small number of personal computers and accessories, such as printers and mobile computing devices. An important function is the sharing of Internet access, often a broadband service through a Subscriber Line (DSL)/Internet Service provider.
A global area network (GAN) is a model for supporting mobile communications across an arbitrary number of wireless LANs, satellite coverage areas, etc. The key challenge in mobile communications is handing off the user communications from one local coverage area to the next. In IEEE Project 802, this involves a succession of terrestrial WIRELESS local area networks (WLAN).
4.Topologies in computer network
In computer networking, topology refers to the layout of connected devices. Think of a topology as a network's virtual shape or structure. This shape does not necessarily correspond to the actual physical layout of the devices on the network. Some of the network topologies include Bus, Ring, Star, Tree. The Network topologies can be visualized in image here, and video presentation here.
more details about OSI @ Wikipedia ,the free encyclopedia
The Open Systems Interconnection Reference Model (OSI Reference Model or OSI Model) is an abstract description for layered communications and computer network protocol design. It was developed as part of the Open Systems Interconnection (OSI) initiative. In its most basic form, it divides network architecture into seven layers which, from top to bottom, are the Application, Presentation, Session, Transport, Network, Data-Link, and Physical Layers. It is therefore often referred to as the OSI Seven Layer Model.
| OSI Model | |||
| Data unit | Layer | Function | |
| Host
| Data | 7. Application | Network process to application |
| 6. Presentation | Data representation and encryption | ||
| 5. Session | Interhost communication | ||
| Segment | 4. Transport | End-to-end connections and reliability | |
| Media
| Packet | 3. Network | Path determination and logical addressing |
| Frame | 2. Data Link | Physical addressing (MAC & LLC) | |
| Bit | 1. Physical | Media, signal and binary transmission | |
- Physical layer conveys the bit stream - electrical impulse, light or radio signal -- through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining cables, cards and physical aspects. Fast Ethernet, RS232, and ATM are protocols with physical layer components.
- At data link layer, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization. The data link layer is divided into two sub layers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sub layer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls frame synchronization, flow control and error checking.
- This Network layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, internetworking, error handling, congestion control and packet sequencing.
- Transport layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer.
- Session layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination.
- Presentation layer provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa. The presentation layer works to transform data into the form that the application layer can accept. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer.
- Application layer supports application and end-user processes. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail, and other network software services. Telnet and FTP are applications that exist entirely in the application level. Tiered application architectures are part of this layer
