Data Communication & Computer Network

Unguided medium transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication. Signals are normally broadcast through free space and thus are available to anyone who has a device capable of receiving them. The below figure shows the part of the electromagnetic spectrum, ranging from 3 kHz to 900 THz, used for wireless communication. Unguided signals can travel from the source to the destination in several ways:  Gound propagation ,  Sky propagation  and  Line-of-sight propagation  as shown in below figure. Propagation Modes Ground Propagation:  In this, radio waves travel through the lowest portion of the atmosphere, hugging the Earth. These low-frequency signals emanate in all directions from the transmitting antenna and follow the curvature of the planet. Sky Propagation:  In this, higher-frequency radio waves radiate upward into the ionosphere where they are reflected ba...

  Guided media, which are those that provide a conduit from one device to another, include   Twisted-Pair Cable ,   Coaxial Cable , and   Fibre-Optic Cable . A signal travelling along any of these media is directed and contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic (copper) conductors that accept and transport signals in the form of electric current.  Optical fibre  is a cable that accepts and transports signals in the form of light. Twisted Pair Cable This cable is the most commonly used and is cheaper than others. It is lightweight, cheap, can be installed easily, and they support many different types of network. Some important points : Its frequency range is 0 to 3.5 kHz. Typical attenuation is 0.2 dB/Km @ 1kHz. Typical delay is 50 µs/km. Repeater spacing is 2km. A twisted pair consists of two conductors(normally copper), each with its own plastic insulation, twisted together. One of these wires is used to car...