"56Kbps modem" (was "TightVNC 1.2.2, is it beneficial?")

[David Brodbeck]

Well, because it *can* receive data at 56Kbps downstream, when connected to
the right sort of equipment at the other end, and that's all most people
care about.  I'll admit it's a bit shady that the fact that it's only 33.6
upstream, or when connected to another, identical modem is hidden in the
"fine print", but most people use these modems for web browsing and file
downloading and don't really care.

Oh yeah, in practice the fastest they can run in the U.S. is 54Kbps.  The
amount of bandwidth and power that would be put into the phone line to get
an actual 56Kbps would violate FCC rules.  56Kbps is strictly a theoretical
figure.  (And on most phone lines they seem to top out at 49Kbps, in my
experience.)

-----Original Message-----
From: Shing-Fat Fred Ma [mailto:fma "at" doe.carleton.ca]
Sent: Monday, February 11, 2002 2:38 AM
To: vnc-list "at" uk.research.att.com
Subject: "56Kbps modem" (was "TightVNC 1.2.2, is it beneficial?")


Hmmm, that's interesting.  So the 56Kbps limit is only because
ISDN defines the channel to like that (whatever the official name
for a channel in ISDN).  So according to your explanation, the
56Kbps doesn't refer to the modem's ability to modulate bits
onto the voice band at all.  Why don't they just call it a
33.2Kbps modem, if that is what it's actually doing?

Fred
--------------------------------------------------------------------------
Fred Ma
Department of Electronics
Carleton University, Mackenzie Building
1125 Colonel By Drive
Ottawa, Ontario
Canada     K1S 5B6
fma "at" doe.carleton.ca
==========================================================================

> Date: Mon, 11 Feb 2002 12:07:49 +1100
> From: Chris Jaecker <cjaecker "at" illustratednetworks.com>
> Subject: Re: TightVNC 1.2.2, is it beneficial?
>
> Fred,
>
> Just a quick clarification here:- 56k modems do not operate at 56Kbps, at
> least not bi-directionally. Modems in general convert digital information
> (bits) into analog (electrical representations of sound), and back.
> Operating properly, a 56K modem converts the bits from your computer into
> analog to cross your local loop (the two wires from your "telephone" to
the
> telephone exchange) and then it is converted to digital signals at the
> local telephone exchange and delivered through the phone network to an
ISDN
> Primary Rate interface at the other end. Throughput from your computer is
> at about 33.2Kbps. The data coming from the other end (which is a router
or
> access server connected to an ISDN network) does not need to be converted
> from digital to analog because ISDN is digital. So data coming in from the
> other end is sent at 56kbps.
>
> If you connect two 56K modems through the telephone system, they'll never
> go faster than 33.2Kbps, as they are both having to do the digital/analog
> conversions. Only when you connect to an ISDN device (e.g. at your ISP),
> will the traffic to you be sent at 56K. Any kind of noise or attenuation
of
> signal will lower this of course.
>
> So "about half" is actually "about right"...
>
> Best wishes
>
> Chris Jaecker
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