chapter 3
DESCRIPTION
CHAPTER 3. Physical Layer. Announcements and Outline. Recap Application Layer 2.1Hardware 2.2Application Architecture (Software) 2.3Web 2.4Email Outline Physical Layer 3.1Circuits 3.2Media 3.3 Digital Transmission (Digital Data) 3.4Analog Transmission (Digital Data) - PowerPoint PPT PresentationTRANSCRIPT
Physical Layer
CHAPTER 3
OutlineRecap2. Application Layer
2.1 Hardware2.2 Application Architecture (Software)2.3 Web2.4 Email
Outline3. Physical Layer
3.1 Circuits3.2 Media3.3 Digital Transmission (Digital Data)3.4 Analog Transmission (Digital Data)3.5 Digital Transmission (Analog Data)
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Network Layers
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Computer 1 Computer 2
Acronyms• FDM – Frequency Division Multiplexing
• TDM – Time Division Multiplexing
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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.
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Physical Layer
Network Layer
Data Link Layer
3.1.2 Circuit Configurations
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Basic physical layout of the circuit
Configuration types:
Point-to-Point Configuration
Multipoint Configuration
3.1.2.1 Point-to-Point Configuration
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3.1.2.2 Multipoint Configuration
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3.1.2 Data Flow (Transmission)
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How does data flow through the circuit
Configuration types:
Simplex
Half-Duplex
Full-Duplex
3.1.2 Data Flow (Transmission)
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3.1.3 Data Flow (Transmission) – Multiplexing
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Combines many low speed circuits into one high speed transmission
Categories of multiplexing
3.1.3 Frequency Division MultiplexingMakes a number of smaller channels from a larger frequency band by dividing the circuit “horizontally”
circuit
FDMFDM
Four terminals
Host computer
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3.1.3 Time Division Multiplexing
Dividing the circuit “vertically”
• TDM allows terminals to send data by taking turns
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3.1.4 Inverse Multiplexing
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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
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Digital Subscriber Line (DSL)
Became popular as a way to increase data rates in the local loop.
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3.2 Media
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Physical matter that carries the transmission
Types:
• Guided Media
• Radiated (Unguided) Media
3.2.1.1 Guided: Twisted Pair (TP) WiresCommonly used for telephones and LANsReduced electromagnetic interferenceTP cables have a number of pairs of wires
Price:
Speed:
Distance:
Common Use:
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3.2.1.1 Guided: Twisted Pair (TP) Wires (CAT5e)
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3.2.1.1 Guided: Comparison of Cables
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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:
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3.2.1.2 Guided: Problems with Copper
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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:
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3.2.1.3 Guided: Fiber Optic CableFiber 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: http://www.youtube.com/watch?v=llI8Mf_faVoCommunication: http://www.ehow.com/video_4951202_optical-fiber-work_.html
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Types of Optical FiberMultimode (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)
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Optical Fiber
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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?
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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
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3.2.2.2 Wireless Media - MicrowaveHigh frequency form of radio communications
Performs same functions as cables
Speed:Distance:
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3.2.2.3 Wireless Media - SatelliteSpecial 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:
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3.2 Factors Used in Media SelectionType of network
Cost
Transmission distance
Security
Error rates
Transmission speeds
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