Calls are Dropping after a few seconds of being answered
This typically means there is no reply to the 200 OK from the Thinktel switch. The 200 OK indicates the call has been answered.
The phone could possibly be:
- Responding to the 200 OK but is routing to the wrong place.
- The phone is responding on the wrong port. ie: port 0
- The phone is responding back to the wrong IP address.
- A SIP aware firewall may be mangling packets or not forwarding SIP ACKs in NAT scenarios. We have seen this behavior in Juniper firewalls.