TDC 461: Basic Telecommunications

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TDC 461 Basic Telecommunications

• DePaul University
• Winter 2001
• LoriLee M. Sadler

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Agenda

• Welcome to TDC 461
• Course Overview
• Syllabus Overview
• Intro to Telecommunications
• Brief History of Telecom

• Voice Characteristics
• Analog vs. Digital
• Telephone Set
• Modems
• Fax Machines

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Course Overview

• What youll get out of this course
• basic concepts and info
• sense of the real world application of telecom
• heightened awareness of legal/social issues
  surrounding telecom technologies
• ability to use your knowledge to evaluate
  proposed systems for feasibility and fit

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Course Overview, cont.

• What do you want to get out of this course?

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Syllabus Overview

• Instructor Info
• Course Logistics
• Grading
• Homeworks
• Exams
• Academic Integrity
• Class schedule

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Class Tools

• Web site
• 461 Web tools

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What is Telecommunications?

• Voice
• Data
• Video
• Integrated

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Why Telecommunications Technology?

• Helps solve communications problems of physical
  distance.
• Helps solve communications problems of physical
  barriers.

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Quality Measures of Telecommunications Systems

• Cost
• Efficiency
• Quality
• Time
• Ease of Use

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Problems in Telecom

• Legacy systems
• Interoperability public standards vs.
  proprietary standards
• Costs

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Communications Networks

• What are they?
• Why do we have them?
• What is required to make them work?

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Network Structure
POP Point of Presence PBX Private Branch
Exchange
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Telecom History1876 - 1998

• Technologies continuously improving
• Regulatory Issues Who pays for all this? How
  much competition?
• Business Issues How much does it cost? What
  services are available?

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History of Transmission Technology

• Through history, voice and data transmission
  systems are getting
• Higher capacity
• Lower cost

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Analog Trunk Technology
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Analog Trunk Technology
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Digital Trunk Technology(T-Carrier hierarchy)
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Digital Trunk TechnologySynchronous Optical
Network (SONET)
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Switching History
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Regulatory History

• Alexander Graham Bell said
• . . . and the lawsuits began.

Watson, Come Here! I need you!
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Regulatory History
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Regulatory History
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Regulatory History
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Regulatory History
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Regulatory History
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Modified Final Judgement1984

• 7 Regional Holding Companies (RHCs) or Regional
  Bell Operating Companies (RBOCs) formed
• Each RHC composed of multiple Local Exchange
  Companies (LECs)
• Interexchange Carriers (IXCs) provide
  long-distance service.

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Regional Holding Companies
US West
NYNEX (Bell Atl)
Pacific Telesis (SBC)
Ameritech
Bell Atlantic
SBC
Bell South
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Modified Final Judgement1984

• Examples
• Ameritech, SBC, Southwestern Bell, etc. are Local
  Exchange Carriers (LECs)
• ATT, MCI, Sprint, etc. are Interexchange
  Carriers (IXCs)

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Network Structure
POP Point of Presence PBX Private Branch
Exchange
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Modified Final Judgement (1984)

• 231 Local Access and Transport Areas (LATAs)
  defined in US.
• LECs can provide only intra-LATA service.
• IXCs provide only inter-LATA service.
• LECs must give customers equal access to all IXCs.

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Problems with MFJ of 1984

• No single company (LEC or IXC) can provide all
  communications services for its customers. This
  is inefficient.
• LATA boundaries limit LEC services.
• Many other companies (Cable TV, Competitive
  Access Carriers, etc.) are not constrained by MFJ.

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The Solution? Deregulation!

• Telecommunications Act of 1996
• Allows IXCs to offer local service
• Allows LECs to offer long-distance service (when
  they can show competition)
• Allows Competitive LECs (CLECs) to share LEC
  facilities (for fair competition).
• Allows combination of voice, data, video service
  packages.

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Telecommunications Act (1996)

• LECs must give competitors
• All services at wholesale prices.
• Access to telephone numbers, operator services,
  directory listings.
• Access to poles, ducts, and right-of-ways.
• Physical co-location of equipment within LEC
  buildings.

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Telecommunications Act (1996)

• A LEC can offer inter-LATA services when
  substantial competition exists on its network.
• The courts are still deciding exactly what this
  means...

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Telecommunications Act (1996)

• Universal Service
• LECs must provide affordable access for
  Schools, Libraries, Health Departments,
  Hospitals, etc.

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Problems - Telecom Act 1996

• IXCs are moving slowly on providing local service
  due to wiring costs.
• LECs are still in court deciding
• Cable TV carriers find it expensive to offer
  voice services over cable.

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The Telephone Set

• Telephone Set
• Handset
• Dial Pad

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What is Speech?

• Speech is a continuous change in air pressure
  over time generated by a vibrating larynx.
• It is an analog waveform (can take any value).
• It is a periodic waveform (repeats itself in time)

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Periodic Signals

• Amplitude (A) signal height volume
• Measured in volts
• Frequency of signal cycles/sec
• Measured in Hertz (cycles per second)

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Periodic Signals

• Example For the signal above
• Amplitude 3 volts
• Fundamental Frequency 100 Hz

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Voice Characteristics
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Bandwidth-Limited Circuits

• analog bandwidthgt
• telephone circuit bandwidthgt
• filteringgt

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Why is Filtering done?

• To save money
• Quality is still good

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Speech TransmissionVarying Air Pressure
Varying Electrical Current
Person produces changes in air pressure via
vibrating larynx.
Carbon granules in telephone receiver produce
varying resistance in response to changes in air
pressure
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Speech Reception Varying Electrical Current
Varying Air Pressure
Changes in air pressure move ear drum and are
interpreted as speech.
Electromagnet in earpiece moves a diaphragm in
response to electrical current changes and
produces varying air pressure.
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Analog vs. Digital Information

• Analog information contains a continuously
  changing stream of values.
• Digital information contains bits (binary digits)
  representing 0 or 1.

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Analog vs. Digital Signals

• Analog signals vary continuously and can take any
  value.
• Digital signals change at discrete times and take
  only fixed discrete values.

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Analog vs. Digital Transmission

• Analog repeater circuits take weak signals and
  amplify them.
• Digital repeater circuits analyze signals,
  amplify and remove accumulated noise.

Regenerator
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Analog Signaling of Digital Data
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Analog Signaling of Digital Data
Analog POTS in the PSTN
Digital ISDN in the PSTN
Digital Network (e.g. ISDN)
Analog Signal
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Digital Signaling of Analog Data

• Analog Data (e.g.voice) needs to be converted
  to/from a digital signal
• for ISDN service, conversion performed in phone
  (or ISDN modem at desk top)
• for analog POTS, conversion performed within line
  card at CO (in switch)

• Conversion is performed by a CODEC (Coder /
  Decoder)

• Desired qualities in a analog signaling scheme
  include
• minimal data rate
• minimal quantization noise
• retention of voice fidelity

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CODEC Operation
CODEC Process

• Sampler samples the analog signal at fixed
  intervals defined by the sampling frequency,
  FSAMPLE.

• Quantizer digitizes PAM samples into discrete
  levels and encodes a n bit binary pattern for
  each quantized sample

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CODEC Operation- analog -gt digital -

• Resulting data rate FSAMPLE x n

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CODEC Operation- digital -gt analog -

• PCM digital bit stream is collected into eight
  bits
• sample is placed in the middle of quantization
  interval defined by binary code
• resulting quantization error lead to quantization
  noise, QNOISE
• signal is sent through a LPFFMAX

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Modems

• Essentially a CODEC
• MOdulate/DEModulate
• Standard Interface

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MODEM Features

• Half duplex vs full duplex

• Synchronous vs asynchronous

• Loopback testing is normally integrated into
  modem

• Modems accept commands to provision and operate
  (e.g. FDXHDX or dial number) using the Hayes
  Command set
• driver software uses the commands to provision
  the modems

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MODEM standards
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Fax Machines

• Operation
• Regulation ITU
• Group 3
• Group 4