Transmission Media

Transmission Media

There are two categories of Transmission Media:

• Guided Media
• Unguided Media

Guided Media: Guided media follow the fixed path for transmission. 

Example: Twisted-pair Cable, Coaxial Cabling, Fiber-optic cabling

Unguided Media : Media in which the signal ate not guided through solid medium are known as Unguided Media.

Example: Radio waves, Micro Waves, Infrared Waves

• A twisted pair of wires consists of two insulated copper wires, typically about 1 mm thickness.
• The wires are twisted together in a helical shape.
• The purpose of twisting the wires is to reduce electrical interference.
• Twisted pair wire are commonly used in local telephone communication and for digital data transmission over short distance up to 1 Km.
• Twisted pair cabling, are of two types:
  • Unshielded twisted pair
  • Shielded twisted pair

• Coaxial cables carry the signal of higher frequency range compared to twisted pair cable.
• Coaxial cables are also cold coax (short form)
• There are two type coaxial cables are widely used : 50 ohm and 75 ohm cable.
• 50 ohm cable is used for digital transmission and 75 ohm cable used for analog transmission.

• Fiber optic cable is made of glass strands that transmit signals as light waves or pulses.
• Each fiber is surrounded by a plastic sheath.
• Fiber optic cable is generally used for backbone for high speed interconnection between networking devices.
• Fiber optic cable can easily handle data at speeds above 1Gbps, it has been demonstrated to handles above data rate exceeding 200Gbps.
• It can handle much higher bandwidth than copper.
• Fiber is lighter than copper.

• Media in which the signals are not guided through a solid medium are known as unguided media.
• Air is the media through which electromagnetic energy can flow easily.
• Therefore, there are several methods which are in use to send electromagnetic energy through air. 
• These methods are:
  • Radio waves
  • Micro waves
  • Infrared Waves

• Electromagnetic waves ranging in frequencies between 10 Kilohertz and 1 gigahertz. 
• Radio waves can be broadcasted Omni directional or  unidirectional.
• Various kind of antennae can be used to broadcast radio signals.
• Radio waves are easy to generate.
• They can travel long distance.

• Above 100 MHz, the waves travel in straight lines and can therefore be narrowly focused.
• Concentrating all the energy into a small beam using a parabolic antenna (like the satellite TV dish) gives much higher signal to noise radio.
• They are used in Cellular phones, satellite networks and wireless LANs.

• Unguided infrared and millimeter waves are widely used for short-range communication.
• The remote controls used on television, VCRs used infrared communication.
• They are relatively directional, cheap and easy to build but do not pass through solid objects.
• Infrared communication is used for indoor wireless LANs.