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From: lstowell@pyrnova.pyramid.com (Lon Stowell)
Newsgroups: comp.dcom.modems
Subject: Re: Telebit T1600 insides & insights...
Message-ID: <141894@pyramid.pyramid.com>
Date: 21 Jan 91 20:13:40 GMT
Sender: daemon@pyramid.pyramid.com
Reply-To: lstowell@pyrnova.pyramid.com (Lon Stowell)
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Organization: Pyramid Technology Corp., Mountain View, CA
Lines: 51

In article <89752@lll-winken.LLNL.GOV> casey@gauss.llnl.gov (Casey Leedom) writes:
>| From: tnixon@hayes.uucp (Toby Nixon)
>| 
>| ... although V.32bis is backward compatible with V.32 and is similar in
>| many respects, it is an order of magnitude more difficult to make a
>| V.32bis modem work _well_. ... This requires much more precise components
>| in the analog portion of the modem ...
>| 
>| It took six years for V.32 modems to become of sufficiently high quality
>| and low price to be acceptable to the broad market.  I just can't see why
>| someone would predict a disaster if it takes a particular company a year
>| to do V.32bis.  I mean, God Forbid everyone doesn't have V.fast modems
>| ready to ship on the day Study Group XVII approves the standard!
>
>  But I want it now! :-)
>
>  Actually, I thought the big issue wasn't analog components -- high
>quality analog components have been available for years -- but the signal
>processing requirements for V.32 that held it up.  It just strikes me that
>all the requisite components are already available to do V.32bis.
>

  Toby knows well of what he speaks.  Actually the analog
  portion of a modem can have considerable effect even at
  V.22bis speeds of 2400 bps.  Having done modem qualification
  testing using a TAS and a live international network, it was
  amazing how much different modems, ALL based on the same
  digital components, differed in their ability to provide
  connections on impaired links.  

  V.32bis is pushing the QAM/Trellis technology considerably
  further than V.32.  It matters not whether the impairments to
  the signal applied to the digital section are impaired inside
  the modem or outside in the telco network--the results are
  poor connections.   

  Virtually ANY V.32/V.32bis modem will connect on average to
  slightly-below average lines. This applies to about 90% or
  more of all lines in North America--just about any V.32 modem
  will provide good connections.  In Europe, this is only 70% or
  fewer of the lines...

  The greater number of code points in the constellation of
  V.32bis makes it more likely that impairments can shift at
  least 2 successive points from their intended
  positions...users of these modems may find it necessary to
  work WITH their local providers to obtain the newly available
  Data Conditioned Local loops--which have values for phase and
  amplitude jitter as well as group delay,-as opposed to the
  older data jack lines which only provide guaranteed loss
  figures at 1 KHz...