Chapter 9 Using Telephone and Cable Networks for Data Transmission

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Chapter 9 Using Telephone and Cable Networks for
Data Transmission

• Telephone Network
• Dial-up Modems
• Digital Subscriber Line
• Cable TV Networks
• Cable TV for Data Transfer

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Telephone Companies Brief History

• Before 1984
• Almost all services are provided by ATT Bell
  System
• In 1984, ATT was broken into
• ATT long Lines
• 23 BOCs(Bell Operating Companies)
• BOCs are grouped together to several RBOCs
• Between 1984 and 1996
• Divided into more than 200 LATAs (Local Access
  Transport Areas)
• After 1996
• Any companies can provide any services

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A Telephone System
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LATAs

• A LATA can be a small or large metropolitan area
• Intra-LATA services are provided by local
  exchange carriers
• ILEC (Incumbent Local Exchange Carriers)
• CLEC (Competitive Local Exchange Carriers)
• Inter-LATA services are handled by IXCs
  (Inter-Exchange Carriers)
• Called long-distance companies

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Switching Offices in a LATA
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POP (Point of Presence)
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Signaling

• In-band signaling the same circuit used for
  both signaling and voice communication
• Out-of-band signaling
• The task of data transfer and signaling are
  separated in modern telephone network
• Signaling system are required to
• Providing dial tone, ring tone, and busy tone
• Transferring telephone numbers between offices
• Maintaining and monitoring the call
• Keeping billing information
• Maintaining and monitoring the status of the
  telephone network equipment
• Providing other functions such as caller ID,
  voice mail, and so on

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Data Transfer and Signaling Networks
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Layers in SS7(Signaling System 7)
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Telephone Network Services

• Analog services
• Analog switched services
• Dial-up service
• 800 service, 900 service
• WATS (wide-area telephone service)
• Analog leased service called a dedicated line
• Digital service
• Switched/56 service
• Digital data service digital leased line

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Dial-Up Modems

• Data signals require a higher degree of accuracy
  to ensure integrity

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Modem

• Modem stands for modulator/demodulator

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Modem Standards

• V-series standards by ITU-T
• V.32 Trellis-coded modulation 32-QAM (4 data
  bits and a redundant bit for error detection) ?
  9,600 bps
• V.32bis 128-QAM (7 bits/baud with 1 bit for
  error control) ? 14,400 bps
• V.34bis 28,800 bps with a 960-point
  constellation and 33,600bps with a 1664-point
  constellation
• V.90 Upload 33.6 kbps, download 56 kbps
• V.92 Upload 48 kbps, download 56 kbps

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V.32 and V.32bis
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V.90 56K Modem

• Traditional modems have a data rate limitation of
  33.6 kbps by Shannon capacity
• Uploading 33.6 kbps
• Downloading 56 kbps
• 8000 samples x 7 bit
• 1 bit for control

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ADSL

• Asymmetrical Digital Subscriber Line
• ADSL is an asymmetric communication technology
  designed for residential users it is not
  suitable for businesses
• The existing local loop can handle bandwidths up
  to 1.1 MHz
• ADSL is an adaptive technology. The system uses a
  data rate based on the condition of the local
  loop line.

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DMT (Discrete Multitone Technique)
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Bandwidth Division in ADSL

• There is no set way that the bandwidth is divided
• Upstream
• 24 channels x 4 kHz x 15 bits/Hz 1.44 Mbps
• Downstream
• 224 channels x 4 kHz x 15 bits/Hz 13.4 Mbps

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DSL Actual Bit Rate

• Because of the high signal/noise ratio
• Upstream
• Normally below 500 kbps
• Downstream
• Normally below 8 Mbps

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Customer Site ADSL Modem
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Telco Site DSLAM

• Digital subscriber line access multiplexer

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Other DSL Technologies xDSL

• HDSL (High-bit-rate DSL)
• Designed as an alternative to the T-1 line (AMI
  encoding)
• 2B1Q encoding used for less susceptible to
  attenuation
• Up to a distance 12,000 ft without repeaters
• Two twisted pairs for full-duplex transmission
• SDSL (Symmetric DSL)
• One twisted pair version of HDSL
• 768 kbps in each direction, symmetric
  communication
• Send and receive data in large volumes in both
  directions
• VDSL (Very-high-bit-rate DSL) Alternative
  approach to ADSL
• Coaxial, fiber-optic, or twisted-pair cable for
  short distances
• Uses DMT with 25-55 Mbps (downstream) and 3.2
  Mbps (upstream)

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Summary of DSL Technologies
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Traditional Cable TV Network

• Started to distribute video signals to locations
  with poor or no reception in the late 1940s
  Unidirectional
• It was called Community Antenna TV

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HFC (Hybrid Fiber Coaxial) Network

• RCH (Regional Cable Head) feeds the distribution
  hubs
• Fiber node splits the signal to each coaxial
  cable
• Communication in an HFC network can be
  bidirectional

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Coaxial Cable Bands

• Video band 6 MHz per TV channel
• Downstream data band 64-QAM (or possibly
  256-QAM)
• Theoretical rate is 30 Mbps (6 MHz/sec x 5
  bits/Hz)
• Upstream data band QPSK
• Theoretical rate is 12 Mbps (6 MHz/sec x 2
  bits/Hz)
• Both upstream and down stream bands are shared by
  the subscribers

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CM (Cable Modem)
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CMTS (Cable Modem Transmission System)
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Data Transmission Schemes DOCSIS

• Standard for data transmission over a HFC network
  by Multimedia Cable Network System (MCNS)
• Data Over Cable System Interface Specification
  (DOCSIS) defines all the protocols to transport
  data from CMTS to a CM