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CHAPTER 3

CHAPTER 3. Physical Layer. Announcements and Outline. Recap Application Layer 2.1 Hardware 2.2 Application Architecture (Software) 2.3 Web 2.4 Email Outline Physical Layer 3.1 Circuits 3.2 Media 3.3 Digital Transmission (Digital Data) 3.4 Analog Transmission (Digital Data)

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CHAPTER 3

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  1. CHAPTER 3 Physical Layer

  2. Announcements and Outline • Recap • Application Layer • 2.1 Hardware • 2.2 Application Architecture (Software) • 2.3 Web • 2.4 Email • 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 Data Link Layer Physical 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.

  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 Configuration • 7

  8. 3.1.2.2 Multipoint Configuration 8

  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. 3.1.4 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 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: 18

  19. 3.2.1.1 Guided: Twisted Pair (TP) Wires (CAT5e) 19

  20. 3.2.1.2 Guided: Coaxial Cable • Less prone to interference than TP due to shield • More expensive than TP, thus quickly disappearing • Price: • Speed: • Distance: • Common Use: 20

  21. 3.2.1.2 Guided: Problems with Copper 21

  22. 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: 22

  23. 3.2.1.3 Guided: Fiber Optic Cable How they are made: http://www.youtube.com/watch?v=llI8Mf_faVo Communication: http://www.ehow.com/video_4951202_optical-fiber-work_.html • 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 23

  24. 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) 24

  25. Optical Fiber 25

  26. 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?

  27. 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 27

  28. 3.2.2.2 Wireless Media - Microwave High frequency form of radio communications Performs same functions as cables Speed: Distance: 28

  29. 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: 29

  30. 3.2 Factors Used in Media Selection • Type of network • Cost • Transmission distance • Security • Error rates • Transmission speeds 30

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