socket connection when Messenger behind router

[s196675m]

There is lot of example for messenger or chat application. I did not find any example which will work when computer is behind router. There are many suggession about port forwarding or router configuration but this is not the case when I use Yahoo, MSN, AOL messsenger, skype or P2P. I don't need to do any configuration in my router for this messenger to work. Is there any idea, example , link how these messenger connect without any router configuration from client side. I read lot of forum but not clear how can I do it. I know how to connect two machine using socket which assumes, machines has public IP address or within local network. I will really appreciate your idea/ suggession. Thank you.

[Migounette]

UPnp or Nat search for this on Google and yoju will understand how it works. In fact it depends on your pre-configured hardware, most of the time UPnp is opened.