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Date:      Sat, 22 Jan 2000 22:03:41 -0500
From:      "Crist J. Clark" <cjc@cc942873-a.ewndsr1.nj.home.com>
To:        Soren Dayton <dayton@overx.com>
Cc:        Majid Almassari <majid@ibroadcast.net>, "freebsd-questions@FreeBSD.ORG" <freebsd-questions@FreeBSD.ORG>
Subject:   Re: Making a 56K Modem Pool
Message-ID:  <20000122220341.A5211@cc942873-a.ewndsr1.nj.home.com>
In-Reply-To: <86d7qtiknk.fsf@polo.overx.com>; from dayton@overx.com on Sat, Jan 22, 2000 at 08:31:11PM -0600
References:  <015d01bf6544$086547e0$1791ddd1@balfourplace.com> <86d7qtiknk.fsf@polo.overx.com>

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On Sat, Jan 22, 2000 at 08:31:11PM -0600, Soren Dayton wrote:
> "Majid Almassari" <majid@ibroadcast.net> writes:
> 
> > Soren Dayton <dayton@overx.com> wrote in message
> > news:86u2k5io06.fsf@polo.overx.com...
> >
> > > Does someone know what's going on here (or know of a pointer to that
> > > kind of information)?  I just don't understand what the issues are,
> > > and I'm going to need to understand these to buy new modems, phone
> > > lines, etc.
> >
> > Unfortunately there is nothing that you can do about it except calling the
> > phone company and complain about noise so they can dispatch a technician to
> > check the wiring in your location at least. Remote testing based on Signal
> > to Noise ratios are not that accurate anyway. There might be wiring problems
> > in your location that a phone tech can determine (like a cross-over
> > wiring-Phone guys know this better that I do?). If everything is OK then you
> > are basically limited and need to switch to a different Technology such as
> > ISDN, XDSL, Cable,...etc.
> 
> Hmm.  Either I don't understand your answer, or I asked the question
> badly.  The setup is two analog modems talking to each other.  Both
> can separately achieve ~51k connections on their respective phone
> lines to various 56k services (such as USR's 56k test line and various
> Chicago ISPs).  However when connecting to each other, they always get
> 33k.  One explanation is that one is configured to max out at 33k in
> one direction.
> 
> The USR/3com guy said, basically, that this is true.  BUT also that
> there are funny protocol issues that require that one of the modems be
> in a "server mode" and speak a "server protocol".  And that these
> kinds of devices only come in ISDN flavors (thus requiring digital
> lines, etc)
> 
> So my question: is this true?  What's the story?  What are references
> that I can look at?
> 
> Does this disagree with what you are saying?  Does it agree?  Did I
> state the question clearly enough?

I am not a modem expert. However, I became aquainted with this issue
when people (including the company GM) whined about how they could
never do better than 33 Kb/s when they dialed into our network.

The 56 Kb/s download and 33.6 Kb/s is an inherent limitation to an
analog connection. There is no way around it. The real reasons the
limit exists are complicated, and I have not sought to fully
understand them. It basically comes down to the fact that a digital
line can talk to an analog line at 56 Kb/s (using the V.90 standard),
but analog can only talk to digial (or another analog) at 33.6 Kb/s
(V.34 I think). It's not intuitively obvious, but it's been a while
since I did any RF signal work.

This URL is a _really_ non-technical overview, but its the best I
could do really quickly. All of the references I previously dug up are
written on paper at the office (that's not very like me...).
-- 
Crist J. Clark                           cjclark@home.com


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