On Aug 9, 2011, at 8:03 AM, Johannes Ebersold wrote:
> I am facing a problem with the binding of the port of the RTSP-Server. The
> Port used by the server is not freed correctly, although the applications
> ends correctly is not killed using ctrl-c, as described
> here:http://www.mail-archive.com/live-devel@lists.live555.com/msg06837.html
Actually, if you read the follow-up messages in that thread, you'll see that
the port (and socket) used by the server *is* freed correctly. However, the
TCP protocol implementation (in the operating system) deliberately waits a few
seconds afterwards before it can mark the TCP connection as being completely
closed (and thus before the port can be reused by another server application
(or rerunning the same server application).
For more information, see
http://www.unixguide.net/network/socketfaq/2.7.shtml
http://developerweb.net/viewtopic.php?id=2941
and
http://www.ssfnet.org/Exchange/tcp/tcpTutorialNotes.html
in particular:
"The main thing to recognize about connection teardown is that a
connection in the TIME_WAIT state cannot move to the CLOSED state until it has
waited for two times the maximum amount of time an IP datagram might live in
the Internet. The reason for this is that while the local side of the
connection has sent an ACK in response to the other side's FIN segment, it does
not know that the ACK was successfully delivered. As a consequence this other
side might re transmit its FIN segment, and this second FIN segment might be
delayed in the network. If the connection were allowed to move directly to the
CLOSED state, then another pair of application processes might come along and
open the same connection, and the delayed FIN segment from the earlier
incarnation of the connection would immediately initiate the termination of the
later incarnation of that connection."
There *is* a potential hack (involving SO_LINGER, as noted in the original
thread) that could eliminate this delay. However, it's non-portable, and
introduces the (albeit remote) possibility of incorrect behavior. So, I won't
be adding this to the code.
If you close a server, just be patient (and wait a few seconds) before trying
to restart it again.
Ross Finlayson
Live Networks, Inc.
http://www.live555.com/
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