CMPE 150

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CMPE 150 Winter 2009

• Lecture 4
• January 15, 2009
• P.E.
  Mantey

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CMPE 150 -- Introduction to Computer Networks

• Instructor Patrick Mantey mantey_at_soe.ucsc.edu
  http//www.soe.ucsc.edu/mantey/
• Office Engr. 2 Room 595J
• Office hours Tuesday 3-5 PM
• TA Anselm Kia akia_at_soe.ucsc.edu
• Web site http//www.soe.ucsc.edu/classes/cmpe150/
  Winter09/
• Text Tannenbaum Computer Networks
• (4th edition available in bookstore, etc. )

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Syllabus

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Assignment 2

• Available on the web site
• http//www.soe.ucsc.edu/classes/cmpe150/Winter09/
• Due Thursday, January 22, 2009

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Todays Agenda

• Physical Layer
• Data Communications
• (Where the data really get moved)
• Theoretical Basis for Data Communications
• Nyquist
• Shannon
• Various Data Channels

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The Theoretical Basis for Data Communication

• Fourier Analysis
• Bandwidth-Limited Signals
• Maximum Data Rate of a Channel

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Bandwidth-Limited Signals

• A binary signal and its root-mean-square Fourier
  amplitudes.
• (b) (c) Successive approximations to the
  original signal.

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Bandwidth-Limited Signals (2)

• (d) (e) Successive approximations to the
  original signal.

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Bandwidth-Limited Signals (3)

• Relation between data rate and harmonics.

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Maximum Data Rate

• Nyquist (1924) (Noiseless capacity)
• capacity C 2H log2V
• where H bandwidth of channel
• V number of discrete levels

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Maximum Data Rate

• Nyquist (1924) (Noiseless capacity)
• capacity C 2H log2V
• where H bandwidth of channel
• V number of discrete levels
• Shannon (1948) (error free capacity)
• capacity C lt H log2 1 S/N
• where S/N signal / noise

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Guided Transmission Data

• Magnetic Media
• Twisted Pair
• Coaxial Cable
• Fiber Optics

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Twisted Pair

• (a) Category 3 UTP.
• (b) Category 5 UTP.

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http//searchnetworking.techtarget.com/sDefinition
/0,,sid7_gci211752,00.html
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Coaxial Cable

• A coaxial cable.

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Fiber Optics

• (a) Three examples of a light ray from inside a
  silica fiber impinging on the air/silica boundary
  at different angles.
• (b) Light trapped by total internal reflection.

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Transmission of Light through Fiber

• Attenuation of light through fiber in the
  infrared region.

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Fiber Cables

• (a) Side view of a single fiber.
• (b) End view of a sheath with three fibers.

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Fiber Cables (2)

• A comparison of semiconductor diodes and LEDs as
  light sources.

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Fiber Optic Networks

• A fiber optic ring with active repeaters.

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Fiber Optic Networks (2)

• A passive star connection in a fiber optics
  network.

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Wireless Transmission

• The Electromagnetic Spectrum
• Radio Transmission
• Microwave Transmission
• Infrared and Millimeter Waves
• Lightwave Transmission

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The Electromagnetic Spectrum

• The electromagnetic spectrum and its uses for
  communication.

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Radio Transmission

• (a) In the VLF, LF, and MF bands, radio waves
  follow the curvature of the earth.
• (b) In the HF band, they bounce off the
  ionosphere.

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Politics of the Electromagnetic Spectrum

• The ISM bands in the United States.

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Lightwave Transmission

• Convection currents can interfere with laser
  communication systems.
• A bidirectional system with two lasers is
  pictured here.

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Communication Satellites

• Geostationary Satellites
• Medium-Earth Orbit Satellites
• Low-Earth Orbit Satellites
• Satellites versus Fiber

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Communication Satellites

• Communication satellites and some of their
  properties, including altitude above the earth,
  round-trip delay time and number of satellites
  needed for global coverage.

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Communication Satellites (2)

• The principal satellite bands.

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Communication Satellites (3)

• VSATs using a hub.

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Low-Earth Orbit SatellitesIridium

• (a) The Iridium satellites from six necklaces
  around the earth.
• (b) 1628 moving cells cover the earth.

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Globalstar

• (a) Relaying in space.
• (b) Relaying on the ground.

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Public Switched Telephone System

• Structure of the Telephone System
• The Politics of Telephones
• The Local Loop Modems, ADSL and Wireless
• Trunks and Multiplexing
• Switching

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Structure of the Telephone System

• (a) Fully-interconnected network.
• (b) Centralized switch.
• (c) Two-level hierarchy.

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Structure of the Telephone System (2)

• A typical circuit route for a medium-distance
  call.

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Major Components of the Telephone System

• Local loops
• Analog twisted pairs going to houses and
  businesses
• Trunks
• Digital fiber optics connecting the switching
  offices
• Switching offices
• Where calls are moved from one trunk to another

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The Politics of Telephones

• The relationship of LATAs, LECs, and IXCs. All
  the circles are LEC switching offices. Each
  hexagon belongs to the IXC whose number is on it.

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The Local Loop Modems, ADSL, and Wireless

• The use of both analog and digital transmissions
  for a computer to computer call. Conversion is
  done by the modems and codecs.

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Modems

• (a) A binary signal
• (b) Amplitude modulation

• (c) Frequency modulation
• (d) Phase modulation

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Modems (2)

• (a) QPSK.
• (b) QAM-16.
• (c) QAM-64.

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Modems (3)
(b)
(a)

• (a) V.32 for 9600 bps.
• (b) V32 bis for 14,400 bps.

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Digital Subscriber Lines

• Bandwidth versus distanced over category 3 UTP
  for DSL.

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Digital Subscriber Lines (2)

• Operation of ADSL using discrete multitone
  modulation.

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Digital Subscriber Lines (3)

• A typical ADSL equipment configuration.

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Wireless Local Loops

• Architecture of an LMDS system.