Voice Communications Concepts Technologies

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Voice Communications Concepts Technologies

• Audio
• Data
• Image
• Video

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Data Communication

• In this context, we mean data already stored on
  computers
• Already digital, no conversion from analog form
  necessary

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Video Communication

• Sequences of images over time
• Same concept as image, but with dimension of time
  added
• Significantly higher bandwidth requirements in
  order to send images (frames) quickly enough
• Similarity of adjacent frames allows for high
  compression rates

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Response Time

• User response time
• System response time
• Network transfer time

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Bandwidth Requirements

• What happens when bandwidth is insufficient?
• How long does it take to become impatient?
• Is data communication ever fast enough?

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Voice CommunicationsConcepts and Technologies

• Essential to understand nature of voice signals,
  as well as how voice signals is integrated into
  network with data transmissions
• Voice communication is increasingly becoming more
  digital in nature.

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Sound

• Several characteristics such as loudness of
  signal, variation in frequency, and distance
  between sender and receiver determines whether
  signal will arrive and make sense to recipient.
• Sound - periodic variation in air pressure
• Sound creates disturbance in media it travels
  across, whether that medium is air or copper
  wire.

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Sound Components

• Three components of sound wave are frequency,
  wavelength, and amplitude of waveform.

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Frequency

• Frequency Number of events happening over
  defined time period.
• Frequency communications measured in Hertz
  (number of cycles per second)
• Frequency of sound is number of times waveform
  represents itself each second

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Frequency, contd
3 cycle
amplitude (volts)
time
(sec)
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Wavelength

• One second - constant reference time used to
  define sounds frequency.
• To fit seven cycles per second into one second
  period, cycles must repeat more often, so length
  of waveform is shorter, as more waveforms are
  forced into same space.

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 Wavelength, contd

• Wavelength term used to describe length of
  waveform.
• Length of waveform is determined by frequency.
• Higher frequency - shorter wavelength lower
  frequency, longer wavelength.

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Wavelength, contd

• Lower frequency longer wave length
• I.e. 5 cycle per second analog wave
• Higher frequency shorter wave length
• I.e. 7 cycle per second analog wave

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Amplitude

• Amplitude - term used to define power or strength
  of signal.
• Amplitude of sound wave determines loudness of
  sound.
• If radio is turned up, amplitude or height of
  sound wave increases.

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Amplitude, contd

• Amplitude of waveform is what determines volume
  of sound as it travels through air.
• Louder you yell, higher waveform and stronger
  signal.

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Human Frequencies

• Speech falls within range of 300 Hz to 4 KHz
  hearing is up to 20 KHz.
• Early telephone engineers used 300 Hz to 4000 Hz
  frequency range when designing telephone network
• Analog telephones use range of 300 Hz to 3400 Hz
• Guardbands prevent interference from adjacent
  frequencies

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Voice Bandwidth
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Sound Waves vs. Electrical Waves

• Electrical waves produced by telephone
  transmitter and traveling down telephone wires
  are referred to as analog signals.
• Analog waveform - analogous to sound waves coming
  from human vocal cords.
• Transmit conversations across copper wires
  because waveforms created by vocal cords can be
  converted to electrical analog signals that
  mirror sound waves.

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Sound Waves vs. Electrical Waves, contd

• Electrical signals travel through conductor much
  faster than sound waves through air
• Voltage induced onto conductor creates current
  flow by exciting electrons, which push against
  one another down wire.

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Power Watts

• Telephone line carries certain amount of energy,
  referred to as watts.
• Watts Measurement term used to define power.
  Light bulb has rating of 60 watts.
• Watts may be viewed as value that defines
  strength of signal. Measure 48 volts, and .6
  mAmps (.006 amps), energy extended is .28 watts.

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Decibels Signal Strength

• Decibel Logarithmic value used to measure
  strength of signal
• dBm Decibel measurement of 1 milliwatt
• If amplitude of signal is too low, result is low
  volume or corrupted data.
• If amplitude is too high, squealing or humming on
  line causes distorted voice signal or corrupted
  data.

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Decibels Signal Strength, contd

• Range between softest sounds humans can hear and
  loudest their eardrums can tolerate is
  one-thousand-trillionth (0.000000000000001) of
  watt to one-thousandth (0.001) of watt.
• Unit used in telecommunications to measure signal
  strength is decibel (dBm).

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Decibels Signal Strength, contd

• If power was 10 milliwatts initially and it
  increases to 20 milliwatts, you added 3 dB of
  gain in signal strength.
• If you increase 20 milliwatts to 40 milliwatts
  you add 3 dB to output.
• Turn radio down from 40 milliwatts to 20
  milliwatts, you decrease signal strength by half
  or take away 3 dB from signal.

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Voice Transmission Basic Concepts

• Shortly,figure will shows mechanics of typical
  phone handset, which consists of both transmitter
  and receiver components.

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Voice Transmission Basic Concepts, contd

• Telephone handset, consisting of both transmitter
  and receiver, is simple device working on
  properties of electromagnetism.
• Human voice spoken into transmitter varies,
  amount of carbon granules striking electrical
  contacts in mouthpiece varies, sending varying
  analog electrical signal out onto voice network.

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Voice Transmission Basic Concepts, contd

• Receiver or earpiece is opposite of transmitter
• Varying levels of electricity produce varying
  levels of magnetism in turn cause diaphragm to
  move in direct proportion to magnetic variance.
• Moving diaphragm produces varying sound waves
  corresponding to sound waves input at transmitter

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Getting Voice Onto and Off Network
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Voice Network Concepts

• Telephone calls are connected from source via
  circuit switching
• Definition of switch in phone system in reserved
  bandwidth connection between two telephone
  handsets
• Capacity on telephone network required to deliver
  call is reserved for use of call.
• Capacity is dedicated to call as soon as it is
  placed

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System Signaling

• Telephone system carries information about call
• Information is referred to as system signaling
• System signaling needs to provide means of
  accomplishing call set-up and termination

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System Signaling, contd

• Basic approaches to sending system signaling data
  across PSTN
• In-band system - signals are sent on same channel
  as voice data itself
• Out of band - inter-switch connections on
  digital PSTN make use of separate channel to
  carry system signaling data

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Signal System 7

• SS7 controls structure and transmission of both
  circuit related and non-circuit-related
  information via out-of-band signaling between CO
  switches.
• SS7 delivers out-of-band signaling via packet
  switched network physically separate from circuit
  switched network that carries actual voice
  traffic.

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Signal System 7, contd

• Coming slide shows characteristics of SS7
  protocols and compares SS7 protocol suite to OSI
  model
• SS7 is described as part of interface between
  users and PSTN known as AIN (Advanced
  Intelligent Network)

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Signaling System 7 Protocols, OSI
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Signal System 7, contd

• Services enabled by AIN include
• Alternate Billing Service (ABS) allows long
  distance call to be billed to calling card, third
  party, or receiver (collect call)
• Custom local area signaling service (CLASS)
  services allow services local to customers
  telephone
• Enhanced 800 service
• Intelligent Call Processing (ICP) Customers are
  able to reroute incoming 800 calls

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Voice Digitization

• Analog signaling effective limited in terms of
  quality, distance, and capacity.
• Long distance poorer quality
• Digital transmission offers better quality and
  higher capacity than analog transmission over
  given media.

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Voice Digitization, contd

• Analog voice conversation must be sampled
  frequently so when digitized version of voice is
  converted back to analog signal, conversion
  resembles voice of call initiator.
• Sampling rate of 8000 samples per second

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Voice Digitization, contd

• Limited number of ways electrical pulses can
  represent characteristics of analog voice signal
• Pulse Amplitude Modulation (PAM) varies
  amplitude or voltage of electrical pulses in
  relation to varying characteristics of voice
  signal

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Voice Digitization, contd

• Pulse Duration Modulation (PDM) also known as
  Pulse Width Modulation(PWM) varies duration of
  each electrical pulse in relation to variances in
  analog signal
• Pulse Position Modulation (PPM) varies
  duration between pulses in relation to variances
  in analog signal
• Coming slide shows techniques

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Voice Digitization PAM, PDM, PPM
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Pulse Code Modulation (PCM)

• Most common voice digitization technique in use
  today
• Coming slide shows basics of PCM
• Eight bits or one byte are required to transmit
  sampled amplitude of analog signal
• 8-bit code allows 28 (256) different values, each
  time actual analog wave is sampled assigned
  value from 0 to 255 depending on amplitude at
  instant sampled

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Pulse Code Modulation (PCM), contd

• Device that samples analog POTS transmission
  coming into local loop and transforms it into
  stream of binary digits using PCM is
  coder/decoder or codec
• Codecs deployed as part of channel bank.
• Channel bank consists of 24 codecs, and
  circuitry required to place digitized PCM voice
  signals onto T-1 circuit

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Pulse Code Modulation (PCM), contd

• DS-0 circuit - transmission capacity of 64 Kbps.
• Twenty-four DS-0s are combined to form T-1, so
  that T-1 can carry simultaneous voice
  conversations digitized via PCM. 
• 8,000 samples/sec 8 bits/sample 64,000
  bits/sec (bps) 
• 64,000 bits/sec 64 Kbps DS-0 Circuit

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Pulse Code Modulation (PCM), contd

• 24 DS-0s 24 64 Kbps 1.536 Mbps
• Plus one framing bit/sample 8,000 samples/sec
  8,000 framing bits/sec
• 8 Kbps 1,536 Kbps 1.544 Mbps transmission
  capacity of T-1 circuit
• Maximum data carrying capacity of T-1 circuit is
  1.536 Mbps framing bits cannot be used to carry
  data.

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Voice Digitization Pulse Code Modulation (PCM)
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Adaptive Differential Pulse Code Modulation
(ADPM)

• More commonly used in Europe
• ADPCM requires half bandwidth for each digitized
  conversation compared with PCM.
• Transmits change in amplitude of consecutive
  amplitude samples, rather than absolute
  amplitude only 32 Kbps of bandwidth is required
  for each conversation digitized via ADPCM

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Adaptive Differential Pulse Code Modulation
(ADPM), contd

• ADPCM calculated difference between predicted
  and actual incoming signals and specifies that
  difference as one of 16 different levels using 4
  bits (24 16).
• Since 4 bits can represent each voice channel,
  ADPCM can support 48 simultaneous voice
  conversations over T-1 circuit

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Voice Compression

• ADPCM is known as voice compression technique
  because of ability to transmit 24 digitized voice
  conversations in half bandwidth required by PCM
• Particular method by which voice is compressed
  may be according to an open or proprietary
  methodology.

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Voice Compression, contd

• Proprietary methods require given vendors
  equipment must be present on both ends of voice
  circuit in question.
• Some voice compression techniques attempt to
  synthesize human voice, other techniques attempt
  to predict actual transmission patterns, and
  still others attempt to transmit only changes in
  voice patterns

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Computer Telephony Integration (CTI)

• CTI seeks to integrate two most common
  productivity devices, computer and telephony, to
  enable increased productivity not otherwise
  possible by using two devices in nonintegrated
  fashion.
• CTI implemented in one of three architectures
• PBX to host interfaces
• Desktop CTI
• Client/server CTI

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Computer Telephony Integration (CTI), contd

• Traditionally, CTI achieved by linking mainframes
  to PBX via proprietary PBX-to-host interfaces
• Individual PCs equipped with telephony boards and
  call control software
• CTI server computer interfaces to PBX to provide
  overall system management while individual client
  based CTI applications execute on multiple client
  PCs.

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Computer Telephony Integration (CTI), contd

• Coming slide shows various CTI architectures
• CTI applications must integrate with different
  computing platforms and OS
• Application portability is possible if
  applications support common commands and systems
  referred to as application program interfaces
  (API)

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CTI Architectures
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Voice Transmission Alternatives

• Voice over IP (VOIP)
• Voice Over Frame Relay
• Voice over ATM
• Voice/Data Multiplexers
• Voice/Data Modems
• ISDN (Integrated Services Digital Network)

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Voice over IP (VOIP)

• VOIP voice - underlying transport protocols of
  Internet that dial over voice conversations.
• Voice over IP refers to technology used to
  transmit voice over any network running IP
  protocol.

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VOIP Transmiss-ion Technology and Topologies
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Voice Over Frame Relay

• Frame relay - transmission initially deployed for
  data transmission but capable of delivering voice
  transmission
• Frame relay encapsulates segments of data
  transfer session into variable length frames
• Variable length frames introduce varying amounts
  of delay resulting from processing by
  intermediate switches on frame relay network

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Voice Over Frame Relay, contd

• Variable length delay introduced by variable
  length frames works data but unacceptable to
  voice
• FRAD (Frame Relay Access Device) can accommodate
  both voice and data traffic using any or all of
  following techniques
• Voice prioritization Prioritizes voice over
  data
• Data frame size limitation Long data frames
  must be segmented into multiple smaller frames
• Separate voice and data queues separate queues
  for data and voice messages

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Voice Over Frame Relay, contd

• Voice conversations transmitted over frame relay
  networks require 4 to 16 Kbps of bandwidth each.
• Dedicated bandwidth reserved as end-to-end
  connection through frame relay network known as
  PVC (Permanent Virtual Circuit).

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Voice Over Frame Relay, contd

• Intermediate frame relay switches within frame
  relay network must support prioritization
  schemes.
• Presently voice conversations can take place only
  between locations connected directly to frame
  relay network.
• Coming slide shows voice transmission over frame
  relay network

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Voice Transmission over Frame Relay Network
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Voice over ATM

• ATM switched based WAN service using fixed length
  frames referred to as cells
• Fixed length cells ensure fixed length processing
  time by ATM switches, thereby enabling
  predictable
• Voice transmitted across ATM networks using
  bandwidth reservation scheme CBR (constant bit
  rate) analogous to frame relay virtual circuit

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Voice Transmission over an ATM Network
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Voice/Data Multiplexers

• Key difference between switched services as frame
  relay or ATM and leased service as T-1 is
  switched services are tariffed according to
  usage, and leased services are tariffed according
  to flat monthly rate

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Voice/Data Multiplexers, contd

• Voice/data Multiplexers can transmit digitized
  voice and data over single digital transmission
  service by assigning voice and data transmissions
  to separate channels

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Voice/Data Modems

• Standards exist for transmission of voice and
  data over single analog phone line
• ASVE (Analog Simultaneous Voice and Data) does
  not transmit voice and data in truly simultaneous
  manner.
• It switches quickly between voice and data
  transmission.
• Voice transmission takes priority, so data
  transfers are paused during data transmissions.

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Voice/Data Modems, contd

• DSVD (Digital Simultaneous Voice and Data) -
  digitizes voice transmissions and combines
  digitized voice and data over single analog
  transmission line

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ISDN (Integrated Services Digital Network)

• ISDN is switched digital service, rather than
  analog capable of transmitting voice and data
  simultaneously
• ISDN (BRI) service offers two 64 Kbps channels.
• One of these channels is used for data and other
  used to transmit voice.

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ISDN (Integrated Services Digital Network), contd

• Analog phones can be interfaced to ISDN
  data/voice modem to allow analog devices to
  access ISDNs digital transmission service.
• Point-to-point ISDN connections requires both
  ends of transmission to be able to access ISDN
  services via ISDN data/voice modems.

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ISDN (Integrated Services Digital Network), contd

• Coming slide shows differences between
  simultaneous voice and data transmission using
  DSVD modems on analog services and ISDN
  data/voice modems over ISDN services

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Simultaneous Voice/Data Transmission with DSVD
and ISDN