After many tests and disappointing results i put this question to the community:
When I open a video on a web side ( real, or mp4 streaming) I get strange results. I can watch these videos when I am online through GPRS/or UMTS. But as soon as i try to do so via WLAN i get either a connection error or a time out. I have tried to identify the problem by changing all possible network settings on the cell phone including the real player on the mobile. i have also preloaded the realplayer to make sure i get no time out. Then i tried to watch streamed videos through my LAN on a home computer. this works perfectly as long as I am in the same subnet on my WLAN at home.As soon as I connect through for example another router, which i connect to my normal router, I get time out again. It seems to me that NOKIA supports the telecom provider by blocking the N95 to connect for streams through WLAN.