[asterisk-users] Asterisk hangs up call after 20s

[Gilles]

Hello

	I have an Asterisk 1.4 server and two XLite softphones, where
Asterisk and the local XLite phone are located in a LAN behind a NAT
router, and the remote XLite phone is located elsewhere on the Net
behind its own NAT router:

http://img252.imageshack.us/img252/3749/asterisknat.png

I'm having the following issue: When the _local_ XLite calls out the
remote XLite, everything works fine; However, when the _remote_ XLite
calls the local XLite, things work OK until precisely 20s, where
Asterisk decides to hang up, and displays the following error message
in the console:

==================
WARNING[593]: chan_sip.c:1948 retrans_pkt: Maximum retries exceeded on
transmission
e45ed578253b9f3dMTRiYTg2OTI0YjExYjUzZWFiNDk3ZjZjMmRlMTQ4NjM. for seqno
2 (Critical Response)

WARNING[593]: chan_sip.c:1972 retrans_pkt: Hanging up call
e45ed578253b9f3dMTRiYTg2OTI0YjExYjUzZWFiNDk3ZjZjMmRlMTQ4NjM. - no
reply to our critical packet.
  == Spawn extension (my-phones, local-xlite-extension, 1) exited
non-zero on 'SIP/unused-008008e4'
==================

I'm no SIP expert, but based on the debug session, before deciding to
hang up, Asterisk tries 6 times to send an OK message to the remote
XLite, and doesn't seem to get an answer. FWIW, after Asterisk has
hung up, the remote XLite remains off-hook, oblivious to this error
and keeps displaying "Call established":

www.pastebin.com/x6MgnrpG

There's also this oddity on line 50: "Scheduling destruction of SIP
dialog".

FWIW, in sip.conf, for the remote XLite user, I tried "nat=no" and
"nat=yes", with no difference. I'm actually not sure how to configure
a remote user which happens to be listed in sip.conf (it's behind a
NAT router but it registers with Asterisk, so... is it NATed or not?),
and am surprised it actually rings and sends/receives voice with no
problem, regardless of this parameter.

I found discussions about using "t1min=500" in sip.conf, but it made
no difference either.

Has someone already experienced this and knows what can be done?

Any hint much appreciated.