I'S' 3413 Introduction to Telecommunications in Business

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I.S. 3413Introduction to Telecommunications in
Business

• Chapter 3
• Analog and Digital Communications Concepts
• Dr. Jan Clark
• SPRING, 003

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Analog - Digital Transmission
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Modulating a Carrier Wave

• Amplitude Modulation - alter height of wave
• Frequency Modulation - alter number of cycles per
  second
• Phase Modulation - direction in which wave begins

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Converting Digital Data to Analog Signals

• Modem (modulator/demodulator)
• Amplitude Shift Keying (ASK) - convert digital
  signal to AM
• Frequency Shift Keying (FSK) - convert digital
  signal to FM
• Phase Shift Keying (PSK) - convert digital signal
  to PM

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Analog Representation of Digital Data
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Amplitude Shift Keying
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Frequency Shift Keying
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Phase Modulation and PSK

• Note how each 1 bit starts on up slope, and each
  0 bit starts on down slope

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Sending Multiple Bits Simultaneously

• Each of the three modulation techniques (AM, FM,
  PM) can send more than one bit at a time.
• Can send two bits on one wave by defining four
  different amplitudes (0 and 1 bit for bit A, 0
  and 1 bit for bit B
• Maximum is around 5 bits simultaneously - same
  modulation method
• If combine modulation techniques can transmit up
  to 10 bits simultaneously
• more error prone

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Sending Multiple Bits Simultaneously
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Multiple Conversions
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Pulse Code Modulation

• Digital representation of analog data

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Baseband Transmission

• Transmission of digital signals in binary format
• In order to successfully send and receive a
  message, both the sender and receiver have to
  agree on data rate (number of bits sent per
  second)

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Types of Baseband Transmission

• Unipolar - voltage is always positive or
  negative (like a dc current). Presence of
  voltage 1, zero voltage 0
• Bipolar - negative voltage 0, positive voltage
  1 (ac current)
• Generally has fewer errors than unipolar
  signaling because the signals are more distinct

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Baseband Transmission
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Manchester Encoding

• Special type of unipolar signaling
• Signal is changed from a high to low or low to
  high in the middle of the signal
• 1 low to high voltage (Fig. 3.11)
• 0 high to low voltage
• Less susceptible to having errors go undetected
• Commonly used in local area networks (ethernet,
  token ring).

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Standard vs Manchester Encoding
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Benefits of Digital Transmission

• Produces fewer errors than analog transmission
• More efficient (TDM more efficient than FDM)
• Higher maximum transmission rates (fiber optic)
• More secure, easier to encrypt
• Simpler integration of voice, data, and video on
  same circuit

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Bit Rate Versus Baud Rate

• Bit rate - number of bits transmitted per second
  also known as data rate
• Baud rate - unit of signaling speed - the number
  of times a signal on the communications circuit
  changes (frequency, amplitude or phase)
• Bit rate baud rate ONLY IF one bit is sent on
  each signal
• If send four bits on each signal, bit rate is 4
  times the baud rate (e.g. 2400 baud, but
  240049600 bits per second (bandwidth))

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Definition of Terms

• Attenuation - Decrease in signal strength -
  (associated with distance, high frequency)
• Amplifier - analog signal booster - can also
  boost noise
• Repeater - regenerate digital signal
• T-carrier - multi-channel digital transmission
  method
• NADH - North American Digital Hierarchy -
  multiplexed T1 lines (de facto proprietary
  standard)

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T-Carrier Rates
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E-Carrier (European) Data Rates

• Do not follow T-Carrier standard

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Why a Fractional T-1?
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Example Leased T-1
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Analog/Digital Summary