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Article: 13265 of comp.protocols.kermit.misc
Path: newsmaster.cc.columbia.edu!panix!newsxfer.eecs.umich.edu!news.cc.ukans.edu!logbridge.uoregon.edu!newsfeed.stanford.edu!postnews1.google.com!not-for-mail
From: satprof@altavista.com (satprof)
Newsgroups: comp.protocols.kermit.misc
Subject: Experience with K95 over satellite links
Date: 14 Mar 2002 09:31:43 -0800
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Following my posting at the end of Jan, 2002 about evaluating Kermit
for a project to transfer ~70MB of data nightly via a double(!)
satellite hop, it might be useful for others in the future to hear of
my experiences.
The requirement was for a highly reliable, automated multi-megabyte
file transfer between two sites (in Africa) connected by IP over
satellite links, with a theoretical bandwidth above 300Kb/s. Each link
goes to a hub in Denmark, meaning that the connection has a _minimum_
ping time of around 1300mSec. Both ends of the link would be running
Windows NT4.0.
To begin, the data turned out to be around 180MB rather than 70MB, but
that is not all that significant, but goes to show the capability of
the system.
The approach I adopted was to set up the K95D.EXE 'daemon' on the
machine holding the data & to script the file transfer on the machine
to which the data was to be sent. Before leaving for Africa, I tested
the script (based on the 'reliable file transfer' script in the K95
'scripts' folder) between my home in France & my office in Geneva.
With an ADSL link at home (& T3 at the office) my tests showed around
20KB/second. (Ping time ~ 40mSec)
However, on arrival in Africa, I couldn't achieve more than about
3KB/second in practice. The receiving end showed only that a single
window was in use, but that is apparently normal at the receiver. The
sending end showed that sliding windows were in use, but only 5 out of
30 possible. (Packet size settled down to 4000/3999; streaming was off
to ensure block checking & the Fast macro was invoked.)
The relatively slow speed was a bit of a disappointment, but it was
overcome by initiating 5 concurrent instances of Kermit, and
transferring the data in parts. (The data, which is an SQL database
dump file, starts out as 800MB uncompressed, but was already
compressed and split into sections by ARJ32.) The net throughput
achieved is around 15KB/sec. which means the job can easily be done
overnight, which plenty of spare capacity for retries.
I also tried 6 concurrent instances, but found that this gave no
practical improvement in total throughput. As it happens, ARJ-created
file segments are suffixed .ARJ, then .A01 through to .Ann, so my 5
scripts look for segments ending 0 & 1, 2 & 3, and so on, bypassing
.A00, which doesn't exist. The scripts terminate when no more files
are found, which allows the data to change in size over time.
The prime reason for the post is to record this for others, but I'd
also like to thank Frank & the others in the group for their input at
the beginning of the project.
If anyone has any ideas about how to increase the no. of windows
actually used, I'd like to try that out. I also tried to get K95D.EXE
to run as a WINNT service, but without success, so would be interested
to know if anyone has managed this elsewhere.
Thanks again for all your help.