Okay, I have to hand it to Draytek tech support, They sent me a new update for the 2850n that isn't available as a standard download from their site. Upgraded firmware and hey presto the VSS sprang to life with an IP address and then setup as normal. I now have 5 bars on my phone and no additional setup on 2850n. No opening of ports or scripting. Well done tech support. 5 stars.