What is happening is that your router is connecting and using the public IP from your ISP. Then it is creating a private network behind it using private IP address and assigning them to your computer and Tenor with DHCP. You need to do a couple of things. First, you can set the Tenor to a static IP, but it will need to be a private one like what your router is sending. Then you need to configure your router so that the Tenor is in the DMZ. Finally you need to configure the public IP in the Tenor as the external IP address.
You can find most of this information by going to Quintum’s web site, under support page, search for firewall and you will find a document that explains more of this.