Intro to xdsl part 1



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ShortDSL0706

QAM constellations

  • 16 QAM V.29 (4W 9600 bps)
  • V.22bis 2400 bps Codex 9600 (V.29)
  • 2W
  • first non-Bell modem (Carterphone decision)
  • Adaptive equalizer
  • Reduced PAR constellation
  • Today - 9600 fax!
  • 8PSK
  • V.27
  • 4W
  • 4800bps

QAM constellations (cont)

DMT - continued

  • time
  • frequency

xDSL Line Codes

  • PAM
  • IDSL (2B1Q)
  • HDSL2 (with TCM and optionally OPTIS)
  • SDSL
  • QAM/CAP
  • proprietary HDSL/ADSL/VDSL
  • DMT
  • ADSL
  • G.lite
  • VDSL line code war is still raging

Duplexing

  • How do we send information in BOTH directions?
  • Earliest modems used two UTP, one for each direction (4W)
  • Next generation used 1/2 bandwidth for each direction (FDD)
  • Alternative is to use 1/2 the time (TDD)
  • More advanced DSP uses adaptive echo canceling

ADSL FDD Duplexing

  • US uses tones 8 - 32 (below 30 KHz reserved)
  • DS uses 256 tones (FDM from tone 33, EC from tone 8)
  • POTS
  • US
  • DS
  • 8
  • 32
  • 256

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