Transmission Media

Guided Transmission Media

         Twisted Pair

         Coaxial cable

         Optical fiber

Transmission Characteristics of Guided Media

Transmission Media


Band Width

Data Rate

Repeater Spacing

Typical Delay

Frequency  Range

Twisted Pair

Coaxial Cable

0.4 – 1 inch

350 MHz

500 Mb/s

1 – 10 Km

4 µs/km

0 – 500 MHz

Optic Fiber

2-125 µm

2 GHz

2 Gb/s

10 – 100 Km

5 µs/km

186-370 THz

Data rate

Rate of data transmission in bits per second

Repeater Spacing

                                Depends upon the field of electromagnetic waves. If the cable is near telephone or electrical wires then repeater should be closely fitted.

Giga = 109

Tera = 1012 


The difference between the highest and lowest frequencies that an analog communications system can pass as measured in Hertz (Hz) or cycles per second. For example, a telephone accommodates a bandwidth of 3,000 Hz: the difference between the lowest (300 Hz) and highest (3,300 Hz) frequencies it can carry.

Twisted Pair

Twisted Pair – Applications

         Most common medium

         Telephone network(Between house and local exchange (subscriber loop) )

         Within buildings( To private branch exchange (PBX))

         For local area networks (LAN)

Twisted Pair – Pros and Cons


         Easy to work with

         Low data rate

         Short range

Unshielded and Shielded TP

         Unshielded Twisted Pair (UTP)

      Ordinary telephone wire


      Easiest to install

      Suffers from external EM interference

         Shielded Twisted Pair (STP)

      Metal braid or sheathing that reduces interference

      More expensive

      Harder to handle (thick, heavy)

Coaxial Cable

©       Outer conductor is a braided shield.

©       Inner conductor is solid metal.

©       Separated by insulated material.

©       Covered by padding.

©       Co = Common , Axial = Axis                 

Optical Fiber

Optic  = light

Fiber = thread ( very delicate that’s why known as thread ). Data travel with speed of light. It’s a glass tube. Jacket = plastic, cladding = protective layer.

If it’s kept straight then there would be no loss of data, to stop bending we use arms.

To stop the data loss light is injected in a specific angle, this is known as total internal reflection.

This angle of reflection is known as Critical angle, which for water is 42°&° for glass it’s 57°

Optical Fiber – Benefits

N        Greater capacity

N        Smaller size & weight

N        Electromagnetic isolation

N        Greater repeater spacing

Optical Fiber – Applications

N        Long-haul trunks

N        Metropolitan trunks

N        Rural exchange trunks

N        Subscriber loops

N        LANs

LED( Light Emitting Diode ) & ILD ( Injection Laser Diode) are used to convert electrical signal into

 light signal.


Device which convert energy from one form to other form e,g fan is Transducer.

LED & ILD are electrical to optical ( E/O )transducer & photodiode (solar cell) are O/E transducer.

Electrical signal à (e/o)  light à(o/e) electric .

Optical Fiber Transmission Modes