1. An Introduction to Transmission Media
Networking
An Introduction to
Transmission Media

2. Transmission Media
There are several different types of transmission media that are used in modern day networks. Various networking situations and requirements may require distinctly different cable types. Considerations when deciding on type of cabling include:
Speed/Transfer rates
Distance/size
Ease of installation
Resistance to interference
Cost
Number of nodes supported

3. Types of Transmission Guided Unguided Twisted Pair Coaxial Fibre Optic
Medium more important than the signal
Unguided
Atmosphere
Outer Space
Signal more important than the medium

4. Frequency of Transmission

5. Twisted Pair UTP & STP Unshielded Twisted Pair (UTP)
Ordinary telephone wire
Cheapest
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)

6. Unshielded Twisted Pair (UTP)
Twisted pair is made of two copper wires which are covered by plastic. The two insulated wires are twisted together to form the communication line. The purpose of twisting the wires is to avoid electrical interference.
Twisted pair should be familiar to us, since it is widely used in our telephone networks either in the home or the office. Twisted pair can be combined into a cable that may consist of two, four, fifty, or hundreds of pairs. Twisted pair is the basis of transmission media. It supports most of the local telephone networks and modern computer networks.

7. Shielded Twisted Pair (STP)

8. Shielded Twisted Pair (STP)
Twisted pair wire is placed inside a thin metallic shielding, similar to aluminium foil, and is then enclosed in an outer plastic casing. The shielding provides further electrical isolation of the signal-carrying pair of wires.
Shielded twisted pair wires are less susceptible to electrical interference caused by nearby equipment or wires and, in turn, are less likely to cause interference themselves.
Because it is electrically "cleaner," shielded twisted pair wire can carry data at a faster speed than unshielded twisted pair wire can.
The disadvantage of shielded twisted pair wire is that it is physically larger and more expensive than twisted pair wire, and it is more difficult to connect to a terminating block.

9. Coaxial
Coaxial cable contains two conductors, which are insulated from one another. The inner conductor is covered by the dielectric. The outer conductor is covered by a shield. Cable TV is one of the most widely applications of coaxial cable which connects the home viewers to the cable companies. There are many applications for coaxial cable, local networks, short-run computer system links, and long- distance telephone transmission are the important applications of coaxial cable.

10. Coaxial
In a local network, coaxial cable can support different types of traffic and data communication. In the transmission of data between different computers, coaxial cable can serve high speed input and output channels for computer systems.
By using frequency division multiplexing ( FDM ), a coaxial cable can carry more than 10,000 channels at the same time.

11. Fibre Optic
The optical fibre contains three parts. The inner most part is the core, which contains one or more thin fibres that are made of plastic or glass.
Each of the fibres in the core is covered by the cladding. The cladding is a glass or plastic coating which has different optical properties from the core.
The outer most part of the optical fibre is made of plastic or Kevlar, which is called the jacket. The purpose of the jacket is to prevent the destruction from the environment.

12. Fibre Optic
There is a light-emitting diode ( light source ) on one side of the fibre and a photodiode ( light-sensitive receptor ) in the other side of the fibre. The fibre optics equipment transmits the light pulses from one side to the other through the plastic or glass. Because of the better performance and the greater data rate of optical fibre, the application of optical fibre has increased dramatically in long-distance communication and military application.

13. Fibre Optic
Lots of different cable sizes and bandwidths

14. Terrestrial Microwave
Terrestrial microwave transmission is another way of transmitting the data. A pair of microwave antennas which are fitted on the top of towers will transmit signals through the air. The shape of microwave antenna is similar to a dish and is about ten feet wide. The microwave antennas are usually in high places in order to achieve better transmission effect.
Terrestrial microwave is used as an alternatives of coaxial cable and optical fibre, since terrestrial microwave transmission needs less repeaters than that of coaxial cable. The voice transmission, television transmission, and the short point-to-point links between building will be the major application of microwave transmission.

15. Terrestrial Microwave

16. Satellite Microwave
Signals are bounced off satellites from one ground station to another allowing data to be sent round the globe
The most important applications for satellite communication is long-distance telephone transmission, private business networks, and television distribution.

17. Satellite Microwave

18. Other Transmission Methods
Infrared
Initially used in remote controls
portable - no antennae required
inexpensive
limited range
sensitive to orientation of transmitter to receiver
Laser
• Use of light to carry information through
the air (no fibre required)
• A laser bean will stay focussed over a long
distance
• Requires a straight line of sight and can
easily be blocked (e.g., by fog).

19. Conclusion range capacity to carry information cost directionality
We use various transmission media with different properties in terms of:
range
capacity to carry information
cost
directionality
reliability (noise and blocking)