It should probally be written in the manual, but Sitecom has a bad habit of poor documentation
. A quicker solution:
- Go to http://www.sitecom.nl/ (they have a English .com site too, but i saw you are Dutch like me).
- On their site, go to: "Support" > "Drivers en handleidingen".
- On the support page select "Data communication" in Product groep and find the DC-202 in Product.
- Press "Zoek" and scroll down a bit (almost until the end) and you will find a Port Forwarding document.
- Download it, read it and use it to forward your ports.
I know the Port Forwarding Document should be there because i saw it in the list, however i didn't had a change to atually download it. Their site duddenly stopped working. It will hopefully work again when you try it, if not then try again in a few hours/days.