LYNCH@A.ISI.EDU (Dan Lynch) (07/04/87)
Mike and David, You are asking a question that covers many sins. The usual numbers for "open connection" timeouts range from 30-120 seconds. If you are using numbers much smaller than these you wil see lots of timeouts. The problem of selcting the "right" timeout is a bit complex because of what you (the initiator) might be trying to accomplish. E.g., if it is a Telnet session then the user is a human and can abort the (presumably hopeless) connection attempt by some local action (escape character or its functional equivalent on each system -- if you don't have the equivalent of an "interrupt now" initiated by the user from the keyboard, then...) so you may as well select a long timeout (2 minutes) and let the connection get established if at all possible. The same goes for FTP because it is user initiated. However, for mail (SMTP) things can get different. It is usually implemented as a background process that slurps over the file system looking for mail files to send out. If this SMTP process uses a long timeout and it runs into a bunch of mail for a dead site it has to get smart about what is (not) happening and not spend a lot of time waiting for a connection to the dead host. Thus a short timeout (30 seconds) might be in order. Big systems that do lots of mail have had to take more hurculean efforts in this arena, like running a number of SMTP mail processes in parallel and having some scheme for staying out of each other's way... The reason for along timeout can lie with many sources: the local host might not have a good retransmission timout for the original "open packet", the network(s) may be congested, or the remote host may take some time to set up a process to respond to the open request. Anyway, the major crime is to have client programs choosing a timeout that is smaller than the retransmission timeout that the TCP is using to detect a lost packet and try the open SYN again. Dan -------
brescia@CCV.BBN.COM (Mike Brescia) (07/05/87)
I would interpret this question as "What should the open timeout be for
telnet, ftp, and mail user and server programs?" What sort of numbers are used
in the software?
mike
---- forwarded message ----
Received: by multimax.ARPA (4.12/25-eef)
id AA02553; Wed, 1 Jul 87 09:02:23 edt
Date: Wed, 1 Jul 87 09:02:23 edt
From: David Kirschen <kirschen@multimax.ARPA>
Message-Id: <8707011302.AA02553@multimax.ARPA>
Subject: Arpanet Timeouts
Hi - Could you tell me if there is a way to determine if we are
seeing a reasonable number of connection timeouts over the Arpanet?
We get lots of connections failing, for various applications (mail, ftp,
telnet). We'd like to know what the commonly used timeout constant
is (i.e., how long should it take when establishing a connection before
the initiator just gives up?). Thanks !!kirschen@MULTIMAX.ARPA (David Kirschen) (07/06/87)
Date: Thu, 02 Jul 87 11:53:33 -0400
From: Mike Brescia <brescia%ccv.bbn.com@CCV.BBN.COM>
Mike, thanks for getting back to me. I'm not sure what timeout values we
are currently using here - that's why I asked the question. Do you have a
feel for what is "common" around the Arpanet ? I would expect that about
the same timeout limits are used almost everywhere, and I'd like to know
what those values are. We understand that the timeout's are determined by
the software, and we just want to see if we are "in the ballpark" compared
to other sites. Thanks again!
----------------------
I would interpret this question as "What should the open timeout be for
telnet, ftp, and mail user and server programs?" What sort of numbers are
used in the software?
mike
---- forwarded message ----
Received: by multimax.ARPA (4.12/25-eef)
id AA02553; Wed, 1 Jul 87 09:02:23 edt
Date: Wed, 1 Jul 87 09:02:23 edt
From: David Kirschen <kirschen@multimax.ARPA>
Message-Id: <8707011302.AA02553@multimax.ARPA>
Subject: Arpanet Timeouts
Hi - Could you tell me if there is a way to determine if we are
seeing a reasonable number of connection timeouts over the Arpanet?
We get lots of connections failing, for various applications (mail, ftp,
telnet). We'd like to know what the commonly used timeout constant
is (i.e., how long should it take when establishing a connection before
the initiator just gives up?). Thanks !!