[Users] interrupts after 30 secconds

Hello, I have a problem: When someone begins a call from PSTN to my voip network, the session interrupts after 30 secconds. The UA don't receive the ACK message(6)[the ACK doesn't arrive].The scheme below indicate this situation. P.S. This situation happens just with one type of equipment: atcom AG468; with other equipment (atcom AT320ED, audiocodes, atcom AG168) all works fine. Very strange. Thunks. |cisco-gateway| | openser | |UA's| X.X.X.X - public ip adress eth0-X.X.X.Y - public IP 172.17.6.0/24 | eth1-172.17.6.2 | | Invite | Invite | 1 |------------------------------->|----------------------------->| | Trying | Trying | 2 |<-------------------------------|<-----------------------------| | Ringing | Ringing | 3 |<-------------------------------|<-----------------------------| | PRACK | | 4 |------------------------------->| | | 200 ok | 200 ok | 5 |<-------------------------------|<-----------------------------| | ACK | | 6 |------------------------------->| | |................................|..............................|30 s | Bye | Bye | 7 |<-------------------------------|<-----------------------------| | 200 OK | | |------------------------------->| | | | | -- Best regards, Ion Minzu, Specialist Tehnologii Informationale, Administrator de sistem al Centrului de certificare, Administrator VoIP, I.S."Centrul de Telecomunicatii Speciale", tel:250-517 (office), 069501208 (mob), 382869185 (ICQ) mailto:ion.minzu@cts.md