Ubuntu Networking :: VoIP On Livebox - Connection Timing Out

I have a complex network. ADSL broadband comes into the house and connects to an Orange Livebox. An Ethernet cable then connects the Livebox to a more powerful router, a DrayTek Vigor 2710Vn. The reason for this is that the Livebox has a second line capability using Voip, but it is not powerful enough to get around my stone house. The DrayTek router has Voip capability, but as yet Orange will not connect the Voip line to it. I connect to this system with Ubuntu. Android, Windows and I-phone. I can connect to either of the routers, though I usually use the DrayTek.

Voip on the Livebox does not require a computer to run it, you just plug a normal phone into it and use it to get free calls. I actually take this line into a Panasonic telephone switch to give me a 2 line system around the house. The problem with this set-up is that after a short time something happens to the network which prevents Ubuntu computers connecting to it. Windows machines, I-phones and Android phones connect, but Ubuntu does not. If I re-boot the Livebox, or in an extreme case take it back to it's factory settings, the Ubuntu machines can connect again, but it's only temporary.

The fact that fixing Livebox sorts the problem definitely points to Ubuntu being innocent, but at the moment I can't do without the Livebox. That means, for the moment, having to stay with Windows. If I post the output log after a failed connection attempt, all it would show is the connection timing out. Why is Ubuntu so sensitive to network problems that are not of it's making. Is there anything I can do about it other than changing my ISP. I am considering that, but other factors make that difficult.