Yesterday I did some quite extensive testing with Voip Unlimited, who provide SIP Trunks. BT have changed how messages for a new call are sent to the customer. Now, it is sent as a fragmented UDP packet as there is a lot of information contained in the packet. The 2820 works, provided that the firmware is at 3.3.3. Higher versions do not work, as the packet is discarded.

Our customers use phone systems running on Windows called 3CX. It has proved to be very robust - apart from this one problem.

I hope that Draytek will update their firware to allow the use of SIP trunks from anyone including Voip Unlimited.

Kind regards
Richard Crabb

I am probably wrong about this, but this issue you have with versions above 3.3.3 is nothing to do with:

1. The "Accept large incoming fragmented UDP or ICMP packets ...." setting or
2. DoS Settings that can cause havoc with VoIP traffic - especially the "Enable UDP flood defense" setting.

As I said, probably not but I thought I had better check......