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000243_fdc@columbia.edu_Sun Jul 28 12:38:13 EDT 2002.msg
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Article: 13557 of comp.protocols.kermit.misc
Path: newsmaster.cc.columbia.edu!news.columbia.edu!news-not-for-mail
From: fdc@columbia.edu (Frank da Cruz)
Newsgroups: comp.unix.bsd.openbsd.misc,comp.protocols.kermit.misc
Subject: Re: logging input from com/serial port in OpenBSD 2.9
Date: 28 Jul 2002 11:46:45 -0400
Organization: Columbia University
Lines: 35
Message-ID: <ai13l5$nol$1@watsol.cc.columbia.edu>
References: <2f177cd8.0207251119.782a5643@posting.google.com> <2f177cd8.0207251954.3ae1df51@posting.google.com> <ahrl21$5ec$1@watsol.cc.columbia.edu> <3D431E29.5070505@ostecs.com>
NNTP-Posting-Host: watsol.cc.columbia.edu
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Xref: newsmaster.cc.columbia.edu comp.unix.bsd.openbsd.misc:29120 comp.protocols.kermit.misc:13557
In article <3D431E29.5070505@ostecs.com>, mkhomo <mkhomo@ostecs.com> wrote:
: Frank da Cruz wrote:
: > In article <2f177cd8.0207251954.3ae1df51@posting.google.com>,
: > Danathar <dougb@attglobal.net> wrote:
: > : Ahh Kermit, there's something I have'nt heard in a while. Must of been
: > : 10 years since I messed around with that. It must of not crossed my
: > : mind due to the extreme age of the neurons holding that info :)
: > :
: > Yes, time marches on, but we've been busy all those years. Take a look
: > at the website to see what I mean:
: >
: > http://www.columbia.edu/kermit/
:
: Out of curiosity, are they still using kermit for space communications,
: and if so how wide were the sliding windows for say the voyager/rover
: transmissions to Mars, back in '98?
:
Kermit, TCP, X.25, or any other protocol that requires signaling in both
directions is not suitable for space communications. The medium is noisy
and the penalty for retransmissions is prohibitive.
When data is sent from deep space back to earth, the transmission is one-way
and it embodies serious redundancy and error correction codes, which expand
the size of the transmission far beyond what we would tolerate for realtime
terrestrial protocols. Large volumes of data arrive from the spacecraft
mangled almost beyond recognition, and then are reconstructed after the fact
not only from the built-in redundancy of the data (which is not perfect) but
also image-processing or similar techniques.
Kermit sliding windows are fine for satellite communication, out to and
including the moon, and for this it's better than protocols like TCP that
don't support selective retransmission of damaged packets. The greater the
distance, the greater the advantage of selective retransmission.
- Frank