[118901] in Cypherpunks
Re: Unplugged! The biggest hack in history (fwd)
daemon@ATHENA.MIT.EDU (Jim Choate)
Sat Oct 9 20:59:48 1999
From: Jim Choate <ravage@einstein.ssz.com>
Message-Id: <199910100056.TAA12373@einstein.ssz.com>
To: cypherpunks@einstein.ssz.com
Date: Sat, 9 Oct 1999 19:56:34 -0500 (CDT)
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Reply-To: Jim Choate <ravage@einstein.ssz.com>
> Date: Sat, 9 Oct 1999 20:38:57 -0400
> From: Dave Emery <die@die.com>
> Subject: Re: Unplugged! The biggest hack in history (fwd)
> For US Robotics modem firmware the ATI6 and ATI11 commands
> return this information.
And it's worth noting that by the time you get them out of the modem they're
worthless. They tell you what the modem did, not what it is doing.
> Echo (or perhaps more properly near end transmit signal)
> cancellation is done for the entire talking path both to the far end and
> back from the far end. Every component of this path could potentially
> generate echos of the modems own transmit signal, all of which have to
> be calculated from the known transmit data and subtracted out to yeild
> the signal from the other side. While it is true that the purely 4
> wire digital portions (virtually all US telco toll trunking these days)
> of the connection do not in general generate echoes, it is not true that
> echoes of the near end signal are only generated on the local loop
> between the modem and the CO.
Which as I stated "get's aggragated with the switch". Bottem line the
scenario you describe is strictly only accurate if the two modems are
connected by a 2-wire dry pair. It's the exact same reason you can't get
anything over 44k on a 56k in a real world scenario. You also leave out the
active noise cancellation that the subscriber board at the switch does, which
despite your claim to the contrary does in fact reduce the effect of the modem
at the far end.
I deleted the rest of your comments because they rest on your description of
the telco connection model which is inaccurate.
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The Armadillo Group ,::////;::-. James Choate
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