Computer Networks - Physical Mediums

1. Physical Link

2. Physical Links
• In lower level, a network can consist of two or more
computers directly connected by some physical medium,
such as coaxial, twisted pair or an optical cable.
• This physical medium is called as links.
• Transmission medium is also defined as, a medium that
can carry information from a source to a destination.

3. Physical Links Contd…
• Transmission media is classified into two categories,
Guided (Wired)
Unguided (Wireless)

4. Guided Media
– Provide a conduit from one device to another
device.
• Coaxial
• Twisted Pair
• Fiber optic
– Here coaxial and twisted pair cables accept and
transport signal in the form of electrical signals.
– Fiber optic cable accepts and transport signals in
the form of light.
Physical Links Contd…

5. Twisted Pair:
• Consist of two conductors (metallic), each with its
own plastic insulation.
– One wire is used to carry the signals to the receiver.
– Another one for ground reference.
• Interference and cross talk may affect both the wires
and make unwanted noise.
Physical Links Contd…

6. • Twisting the cable makes it probable that both wires
are equally affected by external influences (noise or
crosstalk).
• The receiver calculates the difference between the
two, receives no unwanted signals. The unwanted
signals are mostly canceled out.
• the number of twists per unit of length (e.g., inch) has
some effect on the quality of the cable.
Types,
– Shielded
– Unshielded
Physical Links Contd…

7. Physical Links Contd…

8. Applications:
– Telephone Network
– Local Area Network (10BaseT, 100BaseT)
Coaxial Cable:
• Carries signals of higher frequencies than twisted pair.
• Coaxial has central core conductor of solid copper wire
enclosed in an insulating sheath.
• The outer metallic wrapping serves both as a shield against
noise and as the second conductor, which completes the
circuit.
• This outer conductor is also enclosed in an insulating sheath
Physical Links Contd…

9. Physical Links Contd…
Coaxial Cable

10. Categories of Coaxial cable
Applications
• Cable TV
• Traditional LAN
Physical Links Contd…
Category Use
RG-59 Cable TV
RG-58 Thin Ethernet
RG-11 Thick Ethernet

11. Fiber Optic Cable
 Made of glass or plastic; signals are transmitted as
light pulses from an LED or laser
 Light is also a form of electromagnetic energy
 Speed depends on density of medium it is traveling
through; fastest when in a vacuum, 186,000
miles/second
 Propagation Modes,
• Single Mode
• Multi Mode
Physical Links Contd…

12. Physical Links Contd…

13. Multimode Step-Index

14. Multimode Graded-Index

15. Single Mode

16. Advantages of Fiber Optics
– Higher bandwidth than twisted-pair and coaxial cable; not
limited by medium, but by equipment used to generate and
receive signals
– Noise resistance
– Less signal attenuation
– More resistant to corrosive materials
– Lightweight
– Greater security
Physical Links Contd…

17. • Unguided Medium
Physical Links Contd…