I have a CCM and a H323-gateway at the office. The gateway has a E1 ISDN out to the PSTN. I have now tried to install a Firewall between the CCM/IP-phones and the Gateway.
Outgoing calls to pstn works fine with the FW in between, but incoming calls does not. The call reaches the phone, but gets immidiately disconnected, and I can see 1 missed call on the phone.The caller gets the ringback tone, but the phone does not ring.
The FW only has one rule at the moment, permit any any. I can not see any traffic from/to my phone being dropped on the FW. Routing works fine between CCM/FW/gateway/phones.
Where should I start looking for the problem?