1. Five components of data communication

2. Figure 3.1.A Transmission medium and physical layer
Tx media is located below physical layer and is controlled by it.
So Tx media can be said to belong to layer zero.
Tx media is anything that can carry info from src to dst in form of EM signal.

3. Figure 3.1.B Classes of transmission media

4. Topics discussed in this section:
3.1 GUIDED MEDIA
Guided media, which are those that provide a conduit from one device to another . The signal is directed and contained by physical limits of the medium . Metallic media carries signal in form of electric current while optical media in the form of light.
Topics discussed in this section:
Twisted-Pair Cable Coaxial Cable Fiber-Optic Cable

5. Figure 3.1.1 Twisted-pair cable
Two wires : one for signal and one for reference or ground.
Insulator to avoid shorting of lines .
Why twists?
How many twists?
Noise affects both lines eqally thus at Rx the effect
of noise gets cancelled.
Number of twists per unit length decides the quality of cable.

6. Figure 3.1.2 UTP and STP cables
Unshielded is more in use .
Shielded is by IBM . seldom used outside IBM.
STP has metal braided mesh to prevent noise and crosstalk, but bulkier & expensive.

7. Table 3.1.1 Categories of unshielded twisted-pair cables by EIA

8. Figure 3.1.3 UTP performance

10. Figure UTP connector
RJ stands for registered jack. Has 8 lines. Used in LAN
RJ11 has 2 lines , used in land telephone system.

11. Figure 3.1.5 Coaxial cable It carries higher freq than TP
Outer conductor has two functions: protection from noise & complete the circuit.

13. Table 3.1.2 Categories of coaxial cables
RG : radio govt ratings.
Specifies wire gauge , type of insulator, size of casing etc.
Table Categories of coaxial cables

14. Figure 3.1.6 BNC connectors BNC: Bayone-Neill –concelman
Three types: connector to extend , T connector for taps & terminator
What is the need of terminator?
To prevent reflection of signal else it works as antenna

15. Figure 3.1.7 Coaxial cable performance
Applications:
Was used in analog telephone networks( to carry 1000 voice channels, then
for digital telephone networks ( upto 600Mbps) But now replaced by FOC
2) Cable TV networks also used co-ax , but there also replaced by FOC
3) Ethernet LAN( Thin 10 base2 10Mbps over 200 meters ,
Thick 10base5 10Mbps over 500mtr) but here also it replaced by UTP

16. Optical fiber
Is made of glass or plastic ( glass is costlier than plastic but better quality).
Transmits signal in form of light.

17. Figure 3.1.8 Bending of light ray
Light travels stright in single uniform substance , but when enters into different density material, the ray changes direction.
As long as angle of incidence (I) is less than or equal to critical angle , ray gets refracted, if greater then it gets reflected.
Analogy : throwing a flat stone piece in water

18. Figure 3.1.9Optical fiber
Cladding has less density than core

19. Figure 3.1.10 Propagation modes of transmission of light in FOC

20. Figure Modes

21. Multi-mode fiber
Named because multiple beams from light source move through core in different paths.
Fiber with large core diameter (greater than 10 micrometers)
Divided in two sub types : step and graded index.
Step Index : where density changes abruptly . So rays get
reflected suddenly
Graded index : where density changes gradually, So rays get
reflected smoothly.

22. Single mode fiber:
The most common type of single-mode fiber has a core diameter of 8–10 micrometers and is designed for use in the near infrared
Uses highly focused light , (laser), and propagation of beam almost horizontal.
All beams arrive at Rx together , so least distortion as compared to multimode.
But most costly

23. Acceptance angle
Is the maximum angle ,within which all light rays having angle less than this ,will get reflected internally.

24. Table Fiber types

25. Figure 3.1.11 Fiber construction
The structure of a typical single-mode fiber.
1. Core: 8 µm diameter
2. Cladding: 125 µm dia.
3. Buffer: 250 µm dia.
4. Jacket: 400 µm dia.

26. Figure 3.1.12 Fiber-optic cable connectors
Subscriber channel
Straight tip

28. Figure 3.1.13 Optical fiber performance
Attenuation per Km is very less as compared to UTP and co-ax, so requires less no. of ( 10 times less) repeaters .

29. Advantages of FOC:
Higher BW limited only because of transducers at the ends.
Less signal attenuation: repeater after 50Km
Immunity to EM interference : since propagation by light
Glass is not corrosive but copper
Light weight
Immunity to tapping : copper cable acts as antenna
Disadvantages of FOC:
Expensive installation and maintenance: expertise required
Unidirectional light propagation: so for duplex two FOCs required.
Cost: costlier cable and interfaces
Requires additional devices at both ends to convert electric signal to light and light back to electric signal .
To convert electric signal to light : 1) LED 2) Laser diode
To convert light to electric signal : 1) PIN photodiode
2) PiPN Avalanche diode

30. 1) LED

31. 2) LASER diode

32. 1)PIN photodiode

33. 2) PiPN Avalanche