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000343_news@watsun.cc.columbia.edu _Wed Mar 10 10:06:36 1999.msg
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From: fdc@watsun.cc.columbia.edu (Frank da Cruz)
Subject: Re: Problems with terminating failed sessions when uploading files
Date: 10 Mar 1999 14:57:31 GMT
Organization: Columbia University
Message-ID: <7c618r$7kc$1@newsmaster.cc.columbia.edu>
To: kermit.misc@mailrelay2.cc.columbia.edu
In article <MPG.11508314e773428989681@news.pacific.net.sg>,
Alvin Lee <alee@coldstorage.com.sg> wrote:
: I'm hoping someone can enlight me with my problem.
:
: Currently I'm running Kermit95 on two Windows NT Servers.
: One running k95d.exe with listen to port 3000 using hostmode.bat
: and the other acts as an client to upload and download
: files over two routers using ISDN connections.
:
: I face problem when the current uploading session fail
: due to comms error (ISDN line down) and the session on the
: client can timeout and exit but on the server which running
: k95d.exe session still keep hanging there. As the result, I was
: not able to re-upload the file as the previous 'hang' session is
: still locking up the file.
:
: The only way that I could resolve this is to terminate the session
: on the server manually. I had tried to set all setting as follow:
: set server idle-timeout
: set server timeout
: set receive timeout
: set send timeout
: on both client & server scripts.
: but all this setting is effective on the client, not on the server.
:
: Any and all help would be greatly appreciated!
:
As Jeff replied to your identical kermit-support mail:
TCP/IP does not provide any good indicator of a broken connection.
In most cases, if you have a TCP connection from A to B, and A is waiting
for data from B, but B crashes or is powered off, A's TCP/IP stack
will wait for a very long time before returning a timeout error on the
read. However, if it tries to write to a broken connection, it gets an
error immediately.
Your version Kermit 95 implements a new Kermit protocol enhancement called
"streaming", which is used when both ends know they have a reliable (e.g.
TCP/IP) connection. In this mode of operation, the file receiver does not
send acknowledgements during the data transfer phase, and therefore never
tries to write the connection. Furthermore, knowing the nature of Internet
connections, it doesn't bother to time out, since sometimes it might take
an hour for a packet to arrive.
You can disable streaming with SET STREAMING OFF. This restores the normal
Kermit protocol with its own timeouts and ACKs and NAKs, which will have
the desired effect in your case. If the sender goes offline, the receiver
will time out, send a NAK, and this will cause TCP/IP to report the connection
has been lost.
- Frank