Richard,
I do not know what kind of setup do u have running behind your Binatone router which I am not really familiar with it, I can only say here that you can do allow DMZ if you have that option on your router towards tenor, that way u do not have to play with the ports espeically if you running tftp server, telnet..etc.
By enabling DMZ to the tenor you will allow 2way IP traffic and that should fix your problem.
I am at Hwyking@comcast.net if you have a question.