DKA1A COMPUTER NETWORKING

What is Computer network?

A computer network or data network is a telecommunications network that allows computers to exchange data. In computer networks, networked computing devices pass data to each other along data connections. The connections ( network link ) between nodes are established using either cable media or wireless. The best-known computer network is the internet.

Network computer devices that originate, route and terminate the data are called network nodes. Nodes can include hosts such as servers and personal computers, as well as networking hardware. Two devices are said to be networked when a device is able to exchange information with another device.

Computer networks support applications such as access to the World Wide Web, shared use of application and storage servers, printers, and fax machines, and use of email and instant messaging applications. Computer networks differ in the physical media used to transmit their signals, the communications protocols to organize network traffic, the network's size, topology and organizational intent.

 Network topology

The physical layout of a network is usually somewhat less important than the topology by which network nodes are connected. Most diagrams that are drawn to describe a physical network are therefore topological, rather than geographic. The symbols on these diagrams usually denote network links and network nodes.

Network links

The communication media used to link devices to form a computer network include electrical cable ( HomePNA, power line communication ), optical fiber ( fiber-optic communication ), and radio waves (wireless networking).

A widely adopted  family of communication media used in local area network (LAN) technology is collectively known as Ethernet. Wireless LAN standards use radio waves, or others use infrared signals as a transmission medium. Power line communication uses a building's power cabling to transmit data.

Wired technologies

The orders of the following wired technologies are, roughly, from slowest to fastest transmission speed.

Twisted pair

Twisted pair  wire is the most widely used medium for all telecommunication. Twisted-pair cabling consist of copper wires that are twisted into pairs

Coaxial cable

Coaxial cable is widely used for cable television systems, office buildings, and other work-sites for local area networks. The cables consist of copper or aluminum wire surrounded by an insulating layer (typically a flexible material with a high dielectric constant), which itself is surrounded by a conductive layer. The insulation helps minimize interference and distortion. Transmission speed ranges from 200 million bits per second to more than 500million bits per second.

Optical fiber

An optical fiber is a glass fiber. It uses pulses of light to transmit data. Some advantages of optical fibers over metal wires are less transmission loss, immunity from electromagnetic radiation, and very fast transmission speeds of up to trillions of bits per second. One can use different colors of lights to increase the number of messages being sent over a fiber optic cable.

 Wireless technologies

Terrestrial microwave – Terrestrial microwave communication uses Earth-based transmitters and receivers resembling satellite dishes. Terrestrial microwaves are in the low-gigahertz range, which limits all communications to line-of-sight. Relay stations are spaced approximately 48 km (30 mi) apart.

Communications satellites – Satellites communicate via microwave radio waves, which are not deflected by the Earth's atmosphere. The satellites are stationed in space, typically in geosynchronous orbit 35,400 km (22,000 mi) above the equator. These Earth-orbiting systems are capable of receiving and relaying voice, data, and TV signals.

Radio and spread spectrum technologies – Wireless local area networks use a high-frequency radio technology similar to digital cellular and a low-frequency radio technology. Wireless LANs use spread spectrum technology to enable communication between multiple devices in a limited area. This wireless radio-wave technology known as Wifi.

Modems (MOdulator-DEModulator) are used to connect network nodes via wire not originally designed for digital network traffic, or for wireless. To do this one or more frequencies are modulated by the digital signal to produce an analog signal that can be tailored to give the required properties for transmission.

Repeaters

A repeater is an electronic device that receives a network signal, cleans it of unnecessary noise, and regenerates it. The signal is retransmitted at a higher power level, or to the other side of an obstruction, so that the signal can cover longer distances without degradation.

Routers

A typical home or small office router showing the ADSL telephone line and Ethernet network cable connections. A router is an internetworking device that forwards packets between networks by processing the routing information included in the packet or datagram. The routing information is often processed in conjunction with the routing table. A router uses its routing table to determine where to forward packets.