How does Skype work without port forwarding?

Question

I am designing a p2p application which works on port 30000. My router is not UPnP so I required to forward a port to router. But Sk

Answer 1

You have to use an intermediary server, and initiate communication from the client side. As Yossarian mentioned, from that point one possibility is UDP hole punching. Depending on the type of application (and whether it's truly P2P or not) you might keep the go-between server in place the entire time.