1. CHAPTER 3
Physical Layer

2. Outline Recap Application Layer Hardware
Application Architecture (Software)
Web
Outline
Physical Layer
Circuits
Media
Digital Transmission (Digital Data)
Analog Transmission (Digital Data)
Digital Transmission (Analog Data) 2

3. Sender PDU Receiver HTTP Request HTTP Request TCP HTTP Request TCP
Application
Packet
Transport
Segment
Network
Data
Link
Frame
Physical
HTTP
Request
HTTP
Request
TCP
HTTP
Request
TCP
HTTP
Request IP
TCP
HTTP
Request IP IP
TCP
HTTP
Request
Ethernet
Ethernet IP
TCP
HTTP
Request
Ethernet IP
TCP
HTTP
Request

4. 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

5. Circuit Configurations
Basic physical layout of the circuit
Configuration types:
Point-to-Point Configuration
Multipoint Configuration 5

6. Point-to-Point/Multipoint Configuration6

7. Data Flow (Transmission)
How does data flow through the circuit
Configuration types:
Simplex
Half-Duplex
Full-Duplex 7

8. Data Flow (Transmission)
SERVER
CLIENT
Simplex
Half-Duplex
Full-Duplex 8

9. Data Flow (Transmission) – Multiplexing
Combines many low speed circuits into one high speed transmission
Categories of multiplexing 9

10. 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 10

11. Time Division Multiplexing
Dividing the circuit “vertically”
TDM allows terminals to send data by taking turns 11

12. Multiplexing Wavelength Division Multiplexing (WDM)
A variant of FDM used in fiber optic circuits
Makes use of multiple light wavelengths (colors) to divide circuit into channels
Dense WDM can divide circuit into more than 100 channels per fiber each transmitting at 10 Gbps

13. 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? 13

14. Inverse Multiplexing (IMUX)
Shares the load by sending data over two or more lines 14

15. Media Physical matter that carries the transmission Types:
Guided Media
Radiated (Unguided) Media 15

16. 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: 16

17. 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) 17

18. 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) 18

19. Guided: Coaxial Cable Less prone to interference than TP due to shield
More expensive than TP, thus quickly disappearing
Price:
Speed:
Distance:
Common Use: 19

20. 3.2.1.2 Guided: Problems with Copper20

21. 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: 21

22. 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: 22

23. 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) 23

24. Optical Fiber 24

25. 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?

26. Wireless (Unguided) – WLAN (Radio)
Wireless transmission of electrical waves through air
Each device has a radio transceiver with a specific frequency
Includes
Speed:
Distance 26

27. Wireless Media – Microwave/ Satellite
Microwave: High frequency form of radio communications
Performs same functions as cables
Speed:
Distance:
Satellite: Signals travel at speed of light, yet long propagation delay due to great distance between ground station and satellite 27

28. Factors Used in Media Selection
Type of network
Cost
Transmission distance
Security
Error rates
Transmission speeds 28