1. Transmission
Media

2. Transmission Media
 two major classes
 Conducted or guided media
 use a conductor such as a wire or a fiber optic cable to
move the signal from sender to receiver
 Wireless or unguided media
 use radio waves of different frequencies and do not need
a wire or cable conductor to transmit signals

3. Classes of transmission media

4. Guided Media
 Twisted-Pair Cable
 Coaxial Cable
 Fiber-Optic Cable

5. Twisted Pair Wires
 Consists of two insulated copper wires
arranged in a regular spiral pattern to minimize
the electromagnetic interference between
adjacent pairs.
 Often used at customer facilities and also over
distances to carry voice as well as data
communications.
 Low frequency transmission medium.

6. Copper Wires
 Primary medium to connect computers because
 Inexpensive & easy to install
 Low resistance to electric current
 When wires placed close together in parallel,
interference takes place
 To minimize interference, networks use:
 Twisted pair
 Advantages
 Limits electromagnetic energy emission Plastic coated wires
 Prevents signals from other wires from interfering

7. Twisted Pair

8. Twisted-pair cable

9. Twisted Pair Wires
 Two varieties
 UTP (unshielded twisted pair)
 Each wire is insulated with plastic wrap.
 The plastic insulation is color-banded for identification.
 UTP is ordinary telephone wire.
 UTP can transfer data at 1 to 100Mbps over a distance of 100M.
 STP (shielded twisted pair)
 The pair is wrapped with metallic foil or braid to insulate the
pair from electromagnetic interference.
 The metal covering prevents the penetration of electromagnetic
noise.
 It can eliminate the phenomena called crosstalk.
 Provide better performance at lower data rates.

10. UTP & STP

11. Twisted Pair Wires
 Category 3 UTP
 data rates of up to 10mbps are achievable
 Standard cable for most telephone systems
 Category 5 UTP
 data rates of up to 100mbps are achievable
 more tightly twisted than Category 3 cables
 more expensive, but better performance
 Used in LAN.
 STP
 More expensive, harder to work with

12. Twisted Pair
(a) Category 3 UTP.
(b) Category 5 UTP.

13. 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)
 10Mbps or 100Mbps

14. Twisted Pair Advantages
 Twisted-pair cable is used in telephone lines
for voice and data communications.
 Inexpensive and readily available
 Flexible and light weight
 Easy to work with and install

15. Twisted Pair Disadvantages
 Susceptibility to interference and noise
 Attenuation problem
 For analog, repeaters needed every 5-6km
 For digital, repeaters needed every 2-3km
 Relatively low bandwidth (3000Hz)

16. Coaxial Cable (or Coax)
 Carries the signal of high frequency ranges than
twisted pair cable,
 Bandwidth of up to 400 MHz.
 Coaxial cable has the following layers (starting from
the center): a metallic rod-shaped inner conductor, an
insulator covering the rod, a metallic outer conductor
(shield), an insulator covering the shield, and a plastic
cover.
 Both conductors share a common center axial, hence
the term “co-axial”.

17. Coaxial cable

18. Classification:
 Coaxial cable is classified by size (RG) and by
the cable resistance to electric currents.
 Following are some coaxial cable commonly
used in networking.
 50 ohm , RG-8 and RG-11 for Ethernet.
 75 ohm , RG-59 used for cable TV.
 Transmission rate is 10 mbps.

19. Coax Advantages
 Easy to install
 Coaxial cable is used in cable TV networks and traditional
Ethernet LANs.
 Higher bandwidth
 400 to 600Mhz
 Easy to handle and relatively inexpensive as compared to fiber
optic cables.
 Since it is shielded can span a longer distances at higher data
rates.
 Excellent noise immunity.
 Much less susceptible to interference than twisted pair.

20. Coax Disadvantages
 High attenuation rate makes it expensive over
long distance
 Distance is limited.
 Bulky
 Higher cost compared to twisted pair
 Harder to work with & cable easily get
damaged

21. Fiber Optic Cable
 Fiber-optic cables are composed of a glass or plastic inner core
surrounded by cladding, all encased in an outside jacket.
 Fiber-optic cables carry data signals in the form of light. The
signal is propagated along the inner core by reflection.
 Relatively new transmission medium used by telephone
companies in place of long-distance trunk lines.
 Also used by private companies in implementing local data
communications networks.
 Require a light source with injection laser diode (ILD) or
light-emitting diodes (LED).

22. Fiber Optic Layers
 consists of three concentric sections
plastic jacket glass or plastic fiber core
cladding

23. Refraction

24. Critical Angle

25. Reflection

26. Refraction & Reflection

27. Fiber Optic Types
 Signal propagation in optical fibers can be multimode
(multiple beams from a light source moves through different
path) or single-mode (essentially one beam from a light
source).
 Multimode step-index fiber
 In multimode step-index propagation, the core density is
constant and the light beam changes direction suddenly at
the interface between the core and the cladding.
 Multimode graded-index fiber
 In multimode graded-index propagation, the core density
decreases with distance from the center. This causes a
curving of the light beams.

28. Single mode fiber
•This uses step-index fiber and a highly focused source of light
•Has very low density,which make c=90,so beam becomes almost
horizontal.

29. Fiber Optic Signals
fiber optic multimode
step-index
fiber optic multimode
graded-index
fiber optic single mode

30. Fiber Optic Advantages
 Higher transmission rate of 100Mbps.
 It supports voice,video and data.
 Greater capacity (bandwidth of up to 2 Gbps).
 Smaller size and lighter weight
 Lower attenuation
 Immunity to environmental interference
 Highly secure , it is almost impossible to tap into a
fiber cable.
 Safe and easy installation.
 More compact & lighter than copper wire

31. Fiber Optic Disadvantages
 expensive over short distance
 Unidirectional
 requires highly skilled installers
 adding additional nodes is difficult
 Maintenance and repairing cost is high.