Sometimes during a skype call (at least once during a 2 h call) my internet connection crashes and the only thing I can do to fix it is manually restart my internet box. I am using a Cable modem and a Tenda Router. I assumed this was due port forwarding, so I went and set Port forwarding to ports: 80, 443 and the port that skype is currently using (the one in the little box in the Advanced/Connection tab of skype settings. That didn't seem to do the trick, since skype still keeps disconnecting. What else should I try to fix this issue?
I would try setting your router back to its' defaults. Then in Skype, click on Tools > Options > Advanced > Connection, uncheck all the boxes, save the changes, and restart Skype.
Just let Skype use the random port on that Advanced > Connection page. See if that helps.