Iam not sure about your siemens, but in my DLink, i type in the router address (that will be 192.168.0.1 in the browser's address bar, login , go to the port triggering/forwarding link, select new option, enter the service name, enter the port number to be forwarded, and enter my ip address (to know your ip address, u can start command prompt, and type in ipconfig, that will give ur computers ip) in the ip field.
Thats what i do in my router, but yours must be similar, the layout might chage, but it will be there somewhere, just browse through all the options. Hope that helps.
Cheers!