1. CHAPTER 3
Physical Layer

2. Outline Recap Application Layer 2.1 Hardware
2.2 Application Architecture (Software)
2.3 Web
2.4
Outline
Physical Layer
3.1 Circuits
3.2 Media
3.3 Digital Transmission (Digital Data)
3.4 Analog Transmission (Digital Data)
3.5 Digital Transmission (Analog Data) 2

3. Network Layers
Computer 1
Computer 2

4. Acronyms FDM – Frequency Division Multiplexing
TDM – Time Division Multiplexing 4

5. 3 Physical Layer - Overview
Network Layer
Includes network hardware and circuits
Types of Circuits
Physical circuits connect devices & include actual wires
Logical circuits refer to the transmission characteristics of the circuit
Physical and logical circuits may be the same or different. For example, in multiplexing, one physical wire may carry several logical circuits.
Data Link Layer
Physical Layer

6. 3.1.2 Circuit Configurations
Basic physical layout of the circuit
Configuration types:
Point-to-Point Configuration
Multipoint Configuration 6

7. 3.1.2.1 Point-to-Point Configuration7

8. 3.1.2.2 Multipoint Configuration8

9. 3.1.2 Data Flow (Transmission)
How does data flow through the circuit
Configuration types:
Simplex
Half-Duplex
Full-Duplex 9

10. 3.1.2 Data Flow (Transmission)10

11. 3.1.3 Data Flow (Transmission) – Multiplexing
Combines many low speed circuits into one high speed transmission
Categories of multiplexing 11

12. 3.1.3 Frequency Division Multiplexing
Makes a number of smaller channels from a larger frequency band by dividing the circuit “horizontally”
FDM
FDM
Host computer
circuit
Four terminals 12

13. 3.1.3 Time Division Multiplexing
Dividing the circuit “vertically”
TDM allows terminals to send data by taking turns 13

14. Inverse Multiplexing
Combines a number of low speed circuits to create a single high speed circuit on the opposite ends
Why would companies choose to do this? 14

15. Inverse Multiplexing (IMUX)
Shares the load by sending data over two or more lines 15

16. Digital Subscriber Line (DSL)
Became popular as a way to increase data rates in the local loop. 16

17. 3.2 Media Physical matter that carries the transmission Types:
Guided Media
Radiated (Unguided) Media
Guided:
Transmission flows along a physical guide (media guides the signal across the network)
Examples include twisted pair wiring, coaxial cable and fiber optic cable
Radiated:
No wave guide, the transmission flows through the air or space
Examples include radio such as microwave and satellite, as well as infrared communications 17

18. 3.2.1.1 Guided: Twisted Pair (TP) Wires
Commonly used for telephones and LANs Reduced electromagnetic interference TP cables have a number of pairs of wires Price: Speed: Distance: Common Use:
Interference reduced b/c wires twisted together
Telephone wires: usually has 2 pair (4 wires) with only 2 being used at one time
Ethernet: 4 pairs (8 wires) 18

19. 3.2.1.1 Guided: Twisted Pair (TP) Wires (CAT5e)
Interference reduced b/c wires twisted together
Telephone wires: usually has 2 pair (4 wires) with only 2 being used at one time
Ethernet: 4 pairs (8 wires) 19

20. 3.2.1.1 Guided: Comparison of Cables
Interference reduced b/c wires twisted together
Telephone wires: usually has 2 pair (4 wires) with only 2 being used at one time
Ethernet: 4 pairs (8 wires) 20

21. Guided: Coaxial Cable
Less prone to interference than TP due to shield
More expensive than TP, thus quickly disappearing
Price:
Speed:
Distance:
Common Use: 21

22. 3.2.1.2 Guided: Problems with Copper22

23. 3.2.1.3 Guided: Fiber Optic Cable
Light created by an LED (light-emitting diode) or laser is sent down a thin glass or plastic fiber
Has extremely high capacity, ideal for broadband
Works well under harsh environments
Price:
Speed:
Distance:
Common Use:
Not fragile, nor brittle; Not heavy nor bulky
More resistant to corrosion, fire, water
Highly secure, know when is tapped 23

24. 3.2.1.3 Guided: Fiber Optic Cable
Fiber optic cable structure (from center):
Core (v. small, 5-50 microns, ~ the size of a single hair)
Cladding, which reflects the signal
Protective outer jacket
How they are made:
Communication: 24

25. Types of Optical Fiber Multimode (about 50 micron core)
Earliest fiber-optic systems
Signal spreads out over short distances (up to ~500m)
Inexpensive
Graded index multimode
Reduces the spreading problem by changing the refractive properties of the fiber to refocus the signal
Can be used over distances of up to about 1000 meters
Single mode (about 5 micron core)
Transmits a single direct beam through the cable
Signal can be sent over many miles without spreading
Expensive (requires lasers; difficult to manufacture) 25

26. Optical Fiber 26

27. 3.2.1.3 Guided: Which is faster – Fiber or Copper?
Fiber transmits via light – does that mean it is faster than copper b/c it travels at the speed of light? Data Carrying Capacity What should companies use?

28. 3.2.2.1 Wireless (Unguided) – WLAN (Radio)
Wireless transmission of electrical waves through air
Each device has a radio transceiver with a specific frequency
Includes
Speed:
Distance 28

29. 3.2.2.2 Wireless Media - Microwave
High frequency form of radio communications
Performs same functions as cables
Speed:
Distance: 29

30. 3.2.2.3 Wireless Media - Satellite
Special form of microwave communications
Signals travel at speed of light, yet long propagation delay
due to great distance between ground station and satellite
Speed:
Distance: 30

31. 3.2 Factors Used in Media Selection
Type of network
Cost
Transmission distance
Security
Error rates
Transmission speeds 31