According to that document you need a saprouter.
Might want to re-review that document after you have read this one on saprouters.
I believe your confusion is due to mixed concepts between saprouting and rdp/ direct server access via rdp and what that means to a internet based workstation.
In post 22 you are mixing rdp port with sap ports.
This tells me you really didn't undestand what was being proposed concerning RDP or VPN connections.
From what you have posted you have no saprouter but a linksys router. Your post #22 is for saprouters not a linksys router. The linksys is never going to require a 'secret'.
Both the vpn or rdp with TS services solutions do not require the saprouter.
Note: you were referring sapgui to be the saprouter. Wish I caught this earlier
"In sapgui window, for saprouter string". I thought you meant by sapgui that we were dealing with the sap logon/administration.
If you want a saprouter then you need a server/pc with two nics. One connected to the router and one connected to the sap server network.
As per this diagram
You would forward port 3200 in the linksys to this proxy/saprouter wan port. The saprouter command would be as follows as per the saprouter documentation;
Example for a simple connection string with an application server's IP address (172.16.64.17) and portnumber (3200):
Before you go any further I highly recommend you bring in a SAP consultant. You don't know the correct questions to ask concerning this configuration. I would hate to see you get it working only to find out you opened your sap servers to being hacked.
Perhaps this can get you started;