Chapter 9. HighSpeed Digital Access

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Chapter 9. High-Speed Digital Access

• DSL Technology
• Cable Modem
• SONET

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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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DMT Bandwidth Division

• There is no set way that the bandwidth is divided
• Upstream
• 24 channels 4 Kbaud/sec 15 bits/baud 1.44
  Mbps
• Downstream
• 224 channels 4 Kbaud/sec 15 bits/baud 13.4
  Mbps

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DSL Actual Bit Rate

• Because of the high signal/noise ratio
• Upstream
• 64 Kbps to 1 Mbps
• Downstream
• 500 Kbps to 8 Mbps

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Customer Site ADSL Modem
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Telco Site DSLAM
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Other DSL Technologies xDSL

• SDSL (Symmectric DSL)
• For businesses that send and receive data in
  large volues in both directions
• HDSL (High-bit-rate DSL)
• Designed as an alternative to the T-1 line
• VDSL (Very-high-bit-rate DSL)
• Alternative to ADSL
• Uses coaxial, fiber-optic, twisted-pair cable for
  short distances (300-1800m)
• Uses DMT with a bit rate of 50-55 Mbps
  (downstream) and 1.5-2.5 Mbps (upstream)

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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 with TCM
• Theoretical rate is 30 Mbps (6 Mbaud/sec 5
  bits/baud)
• Upstream data band QPSK
• Theoretical rate is 12 Mbps (6 Mbaud/sec 2
  bits/baud)

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CM (Cable Modem)
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CMTS (Cable Modem Transmission System)
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SONET/SDH

• Digital transmission standards for fiber-optic
  cable
• Independently developed in USA Europe
• SONET(Synchronous Optical Network) by ANSI
• SDH(Synchronous Digital Hierarchy) by ITU-T
• Multiplexed transport mechanism
• Carrier for ATM and B-ISDN

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Interesting Features of SONET/SDH

• SONET/SDH is a synchronous network
• A single clock is used across the entire network
• It contains the standards for fiber-optic
  equipments
• Very flexible to carry other transmission systems
  (DS-0, DS-1, etc)

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SONET/SDH Rates

• SONET defines a signal hierarchy
• STS (Synchronous Transport Signals)
• A hierarchy of signaling levels
• OC (Optical Carriers)
• Physical links defined for optical signals
• STS(OC)-1 (51Mbps) ? STS(OC)-192 (10Gbps)
• SDH specifies a similar hierarchy
• STM (Synchronous Transport Module)
• STM-1 (155Mbps) ? STM-64 (10Gbps)
• OC-1, OC-3, OC-12, OC-48, OC-192

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SONET
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Frame Format STS-1
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SONET Frames STS-1
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SONET Rates
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Virtual Tributaries

• Partial payload that is inserted into an STS-1
  frame
• Each component of subdivided SPE
• Provides backward compatibility
• Four types of VTs
• VT1.5 For DS-1(T-1 1.544Mbps)
• VT2 For CEPT-1(E-1 2.048Mbps)

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VT Types
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STS Multiplexing
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STS-n