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> Since this isn't a modem group I first need to ask what "the DAA for
> high speed QAM modems" means. Furthermore, if they are basically the
> same why do they have different tested performance? Am I missing the
> point?
Sorry. Good questions.
DAA stands for "Data Access Arrangement" It's not worth going
into the politics of why they exist or info how they are designed.
Basically the DAA is the circuitry that couples the modem to the phone
line, protects the line / modem from each other and detects ringing
(sometimes also deals with caller ID).
QAM is Quadrature Amplitude Modulation. Typically QAM is used for modems
2400 baud and above (except for Telebit which used multi-carrier
AM modulation). (Its that noise you hear when modems are talking).
For what its worth, with QAM amplitude and phase reproduction is important.
Many modems use the same chip set (i.e. from AT&T or Rockwell). The only
difference is the manufacture of the modem's implementation of the DAA.
If the DAA does distorts the signal (i.e. adds amplitude or phase
distortion) errors are introduced. This translates into a lower overall
throughput (i.e. lower performance).
--
Scott A. Stratmoen | strat@ast.dsd.northrop.com
| (708) 259-9600 (ex 24762)