Physical Layer CHAPTER 3

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Outline Recap 2.Application Layer 2.1Hardware 2.2Application Architecture (Software) 2.3Web 2.4 Outline 3.Physical Layer 3.1Circuits 3.2Media 3.3 Digital Transmission (Digital Data) 3.4Analog Transmission (Digital Data) 3.5Digital Transmission (Analog Data) 4

Network Layers 5 Computer 1Computer 2

Acronyms FDM – Frequency Division Multiplexing TDM – Time Division Multiplexing 6

3 Physical Layer - Overview 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. 7 Physical Layer Network Layer Data Link Layer

3.1.2 Circuit Configurations 8 Basic physical layout of the circuit Configuration types:  Point-to-Point Configuration  Multipoint Configuration

Point-to-Point Configuration 9

Multipoint Configuration 10

3.1.2 Data Flow (Transmission) 11 How does data flow through the circuit Configuration types:  Simplex  Half-Duplex  Full-Duplex

3.1.2 Data Flow (Transmission) 12

3.1.3 Data Flow (Transmission) – Multiplexing 13 Combines many low speed circuits into one high speed transmission Categories of multiplexing

3.1.3 Frequency Division Multiplexing Makes a number of smaller channels from a larger frequency band by dividing the circuit “horizontally” circuit FDM Four terminals Host computer 14

3.1.3 Time Division Multiplexing Dividing the circuit “vertically” TDM allows terminals to send data by taking turns 15

3.1.4 Inverse Multiplexing 16 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?

Inverse Multiplexing (IMUX) Shares the load by sending data over two or more lines 17

Digital Subscriber Line (DSL) Became popular as a way to increase data rates in the local loop. 18

3.2 Media 19 Physical matter that carries the transmission Types: Guided Media Radiated (Unguided) Media

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: 20

Guided: Twisted Pair (TP) Wires (CAT5e) 21

Guided: Comparison of Cables 22

Guided: Coaxial Cable Less prone to interference than TP due to shield More expensive than TP, thus quickly disappearing Price: Speed: Distance: Common Use: 23

Guided: Problems with Copper 24

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: 25

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: 26

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) 27

Optical Fiber 28

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?

Wireless (Unguided) – WLAN (Radio) Wireless transmission of electrical waves through air Each device has a radio transceiver with a specific frequency Includes  Speed: Distance 30

Wireless Media - Microwave High frequency form of radio communications Performs same functions as cables Speed: Distance: 31

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: 32

3.2 Factors Used in Media Selection Type of network Cost Transmission distance Security Error rates Transmission speeds 33