@chpalmer said in Really Strange Behaviour - Have I been Hacked?:
SIP clients are designed to keep the connection live. 24/7. Some devices are better designed than others.
SIP was not originally designed to be behind NAT. NAT was hacked in (emphasis on hack) later when the idea of marketing to the residential and small business markets. Vonage was sued early on for patent infringement. Since then other carriers are being very careful to keep out of that particular court room and thus everyone does things just a little different.
The problem becomes when you as a customer of one company with their specific devices has an issue trying to find someone that knows that exact system and their requirements/method of operation can be difficult. Generally things are close enough and the knowledge that is bestowed is usually enough. But little things can crop up and stimie everyone..
You don't want your ATA states to expire normally. The whole idea is that a constant connection is kept active between the ATA/phone device and the carrier SIP server. Otherwise you would not be happy with the quality of your VOIP carrier.
Thanks for the reply @chpalmer - As a result of your email, I did a quick pcap to see what what going on (now that my system is functioning normally), and from what I can see the ATA sends a UDP packet about very 20-25s to keep the firewall open.
And I agree with you that documentation of SIP is somewhat "spotty"... you may have uncovered the reason why. I don't know when that was or when the suit occurred, but IIUC a patent is good for 17 years, so it should hopefully be expiring soon as this is a very mature protocol.