There is no need to use that. If the two PCs are in same network, then you can use Remote Desktop to access each other. But Remote Desktop is disabled by default on PCs, can Google it and will know how to use it.

Kevin SG,
You are missing the point. I know exactly how RDP (Remote Desktop) works between computers on THE SAME (LOCAL) NETWORK.
However, if you want to RDP to a computer from outside the local network, then you have to setup the router to forward RDP port (by default 3389) to the specified computer.
Most of routers have the functionality called "Port Forwarding" and it is achieved by this function easily.
I'm not sure that Port Triggering (Archer MR400 does not have Port Forwarding) will do the job.
Anyway. I'm just about to find out, as I bought the modem and will be setting it shortly.

Ah, if you need to access the PC form external network, then need to open ports yes. But it should be Virtual Servers(same as port forwarding).
You may refer to his link: http://www.tp-link.com.au/faq-1675.html