I've tried up and downloading the same 94 text files to a server in NZ, and
ftp sessions don't hang. They only die with servers in the US.

The workarounds are probably all sound, but not many remote hosts allow you
to execute programs to expand archives, and most like files to be
transferred with ftp.

-- Juha

> Here is a theory, on what is causing this.
>
> FTP creates a new TCP connection on port 20 for each data
> transfer (there is an exception, but I'll ignore it for the moment). So
> each file transfer requires a new TCP connection to be build up
> then torn down.

> Transferring a lot of files via FTP in a quick time requires a lot of
> TCP connections. When a TCP connection is to be closed it goes
> through a variety of states then ends up in the TIME_WAIT state
> the TCP connection has to wait in this state for twice the maximum
> segment lifetime (MSL). The size of the MSL is chosen by the
> implementor of your TCP stack. The MSL is commonly 30
> seconds, 60 seconds or 120 seconds. Some TCP stacks have a
> dynamic MSL value.
>
> So after you transfer of a lot of files in a short time your M10 has a
> whole lot of TCP connections sitting around doing nothing but
> waiting to close. I would say that the M10 has some sort of limit
> on the number of TCP connections. Either a limit on a total
> number and/or a limit for each host off the M10. Using just a plain
> modem there isn't really a limit.
>
> So my theory is that you are hitting one of these limits and the
> M10 isn't allowing any more connections until they timeout.
>
> Now how to get around this.
> 1. Combine all the small files into an archive, then expand the
> archive at the host.
> 2. Use a protocol other than FTP
> 3. Use FTP in passive mode. Passive mode is not used much and
> is only found on a few FTP clients (the ftp client that comes with
> Windows doesn't support it). Passive mode reverses the direction
> of the FTP data connection. This would mean that the ftp server
> would be doing the TIME_WAIT. It might not be possible to use
> passive mode through the M10.
>
> or on the other hand it could be something else that is causing this
> problem.
>
>
> --
> Richard Gallagher
> rbg@cvm.co.nz
>
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Received on Sun Oct 31 19:46:10 1999