Computer Networking

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Computer Network	It is a collection of interconnected computers and other devices which are able to communicate with each other and share hardware and software resources.
Transmission Medium	A transmission medium is a medium of data transfer over a network. It can be wired or wireless.
Wired Media	A number of various types of cables are used to transfer data over computer networks.
Twisted Pair Cable	Most widely used cable for creating small computer networks. It contains four twisted pairs covered in an outer shield. These pairs are colour coded. An RJ-45 connecter is used to connect this cable to a computer.
UTP Cable	Unshielded Twisted Pair Cable.
STP Cable	Shielded Twisted Pair Cable. Same as UTP, but with each pair shielded induvidually. Outer shield then covers all the pairs like in UTP. STP data connectors are used to connect STP cable to the computer.
Co-axial Cable (coax)	It consists of two conductors that share a common axis. The inner conductor is a straight wire and the outer conductor is a shield that might be braided or a foil.
Optical Fiber Cable	They are long, thin strands of glass about the thickness of a human hair. They're arranged in bundles and are used to transmit data through light signals over long distances
OFC Core	Thin glass rod at the center through which the light travels
OFC Cladding	Outer optical material surrounding the core that reflects the light back to the core
OFC Buffer Coating	Plastic coating that protects the cable from damage and moisture
Wireless Media	Electromagnetic waves are used for wireless communication over computer networks. Frequencies of waves are measured in Hertz (Hz). Their properties change as frequencies change
Frequencies used for Wireless Communication	Radio waves, Microwaves, Infrared rays
Radio Waves	3KHz - 3GHz. Ex : Walkie Talkie. Distance from a few metres to an entire city. Easy to generate, can travel long distances and can penetrate buildings easily. Widely use for communication both indoor (cordless phones) and outdoors (AM and FM radio).
Micro Waves	0.3 GHz - 300 GHz. No clear cut demarcation b/w radio waves and micro waves. Can travel in straight linesand cannot penetrate any solid object. For long distance, high towers are built and microwave antennas are put on their tops, they have to be aligned with each other.
Infrared Waves	300GHz - 400THz. They are so called because they have a frequency range of just less than that of a red light (400THz - 484THz). Used for short range communication in a variety of wireless communications, monitoring and control applications. Easy to build but cant pass through solid objects.
Bluetooth	2.402GHz - 2.480 GHz. Used for short range comm (10m). Ex Cell phones, door openers etc
Satellite Link	Used for very long distance comm ranging from intercity to intercontinental. Downlink frequency is always lower than uplink.
Communications Satellite	It is a relay station in orbit above the Earth that recieves, regenerates and redirects signals carried on a specific frequency.
NIC	Network Interface Card. It is a device that enables a computer to connecy to a network and communicate. It is an integral part of the motherboard.
Hub	It is an electronic device that connects several nodes to form a network and redirects the recieved information to all the connected nodes in a broadcast mode.
Switch	It is an intellegent device that connects several nodes to form a network and redirects the recieved information only to the intended node(s).
Repeater	It is a device that is used to regenerate a signal which is on its way through a communication channel. A repeater regenerates the recieved signal and re-transmits it to its destination.
Gateway	It is a device which is used to connect different types of networks and perform the necessary translation so that the connected networks can communicate properly.
Node	It is a device which is directly connected to a computer network. It can be a computer or any other device like printer, scanner etc.
Topology	It is an arrangement of physical connections among nodes in a network.
Bus Topology	All nodes are connected to the main cable called backbone. Signal travels through the entire length of the backbone and is recieved by the node for which it is intended. Small device called terminator is attatched at each end of the backbone. When signal reaches the end of backbone, ti sis absorbed by the terminator and the backbone gets free to carry another signal. This elements chances of signal interference as it prevents reflection of signal back on cable.
Star Topology	Each node is directly connected to a hub/switch. The node sends the signal to the hub/switch.
Tree topology	It is a combination of bus and star topologies. It is used to combine multiple star topology networks. All stars are connected together like a bus. It supports the future expandibility of the network.
Network Protocol	It is a set of rules for communication among networked devices. Protocols generally includes rules of how and when a device can send or recieve the data, how is the sent data packaged, and how it reaches its destination.

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