I have a SIP trunk set up with 3 SIP DIDs associated with it. When first created all 3 DIDs would ring in correctly when called, however, I've noticed that after a period of time (roughly 30 minutes) calls to any of those DIDs result in dead air for 5-6 seconds and then give a busy tone. Running a wire capture on it I see a 600 Busy Everywhere code. What's strange is that if this is happening I can pick up a phone and dial out of the phone system and after doing this all incoming calls immediately start ringing in correctly again. Then roughly 30 minutes later they start ringing busy again and I have to dial out before incoming calls will ring in correctly. I've worked with the SIP provider and they are insisting that the issue is not on their side..... 3CX Version 15 by the way.