[Bug 601420] Re: empathy cannot connect to my SIP server

[David Sugar]

There are several reasons why this may happen.  The one I am most
familiar with is a consequence of Empathy using ephemeral ports.  What
happens is that while the SIP port of the Empathy client is bound to
port 5060 to receive SIP messages, when sending a message (such as
registration), the backend for Empathy instead creates a new socket (on
an ephemeral port) to send SIP messages.  Some SIP servers, to support
NAT, assume the UDP port (and address) the incoming SIP message from the
client "appears" from is the place to route return messages, and since
this is a transitory socket, the response is of course lost and the
chain of operation is broken.

Some argue this is a defect of the SIP server, or not standard compliant
behavior, and for this reason upstream (nokia SIP stack) will not change
it, while others point out true standard-compliant behavior would fail
behind NAT, and indeed further, by Empathy not using the same socket to
send registration refreshes, there is also no keyhole keep-alive
possible for NAT on UDP.  However, this does not offer a solution for
your real and immediate issue, but rather simply background as to why it
is currently broken.

One thing I had talked about with the Telepathy developers at UDS is
using sipwitch as a local SIP proxy to solve this, since SIP Witch
actually can deal with the ephemeral port behavior already.  Another
possibility we discussed was perhaps replacing the Nokia SIP stack with
eXosip2.  However, none of these are "immediate" options to fix this.  A
third choice would be to try and get a patch accepted for Nokia SIP.
The SIP Witch approach is one I do have control over, being the
upstream, and I can look at seeing how we can resolve these scenarios.



** Changed in: empathy (Ubuntu)
       Status: New => Confirmed

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empathy cannot connect to my SIP server
https://bugs.launchpad.net/bugs/601420
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