Ekiga and Empathy stop receive incoming calls after 3600 sec on Suse 11.3

On Suse 11.3 86x64 have tried to use Ekiga or Empathy for video calls with sip provider. Configuration passed easy, video and audio works fine for both applications. There were no problems to dial at any time, but a problem appeared with incoming calls . In one hour time after starting application incoming calls are registered and handled correct, after first hour no incoming call was registered in any way. I opened ports 5000:5100 tcp and udp for sip as suggested with no success .
I have no idea what happened after 3600 sec which closes the system for incoming calls. Any idea how I can keep the system receiving incoming calls , except for turning off and on application every 59 minutes.