CS1000 SIP trunk with XO

[CulverTech]

Hi all,

We have a CS1000 5.50 doing sip trunking with XO.  Running into an odd problem, our calls are dropping after exactly 45 minutes.  When I put a sniffer along the path where I can sniff, I see the sig server sending a SIP invite to start the call, then an ACK about .02 seconds after the invite.  It does this again at the 15 minute mark.  Then at the 30 minute mark it sends another invite and an ack .02 seconds apart, only, after this point every 3 seconds there is a sip invite with an ack .02 seconds after.  This goes on every 3 seconds until at the 45 minute mark, there's a BYE message also seem to originate from the sig server.  The SIP bye message actually has a from address of the endpoint. 

From the last invite to the bye the time gap is also exactly 3 seconds.  Has anyone seen this problem?  There is a firewall on the outbound path from the sig server, but it's configured to allow all traffic from the telephony subnet.  Thanks again

Alex

[Michael McNamara]

I had a similar problem but with a Polycom VSX8000 running SIP. The issue here is that the audio path and the control path are usually on different TCP/UDP ports. You should probably look into your firewall settings around idle TCP/UDP timeouts, or if the firewall is new enough enable any SIP handling (statefullness) features.

If you look at the firewall log you should see the different ports and some of them getting reject around 45 minutes. I would bet that your firewall has a timer somewhere set for 45 minutes.

Here's a post I did about Check Point firewalls a while back;
http://blog.michaelfmcnamara.com/2010/12/check-point-firewall-1-maximum-concurrent-connections/

Good Luck!

[CulverTech]

Just an update on this one.  I finally got access to the data switch and was able to put a sniffer right outside the XO router.  Now I see that the sig server sent out a re-invite at the 15 minute mark, the xo router replied with a 100 trying and 200 ok, then the sig server replied with an ACK.  At the 30 minute mark, the sig server sent out another re-invite with a higher cseq #.  To that the XO router replied with a 491 Request pending.  So it looks like the XO router is thinking all the reinvites are duplicates of that one sent out at the 15 minute mark and just ignored them.

I'm no expert with the SIP protocol, other than the ACK, should the sig server be sending something else to end that first reinvite dialog?  Or should increasing that cseq number be enough to tell the other end to process the new reinvite request?  Thanks again

Alex

[CulverTech]

Got a response form XO saying this is because we don't have SDP sent out along with our re-invite.  So the question is, how do I make our sig server to send out SDP with our SIP invites?  Is that even possible with the CS1000 5.5?