Ports to be open for iTunes U

Hi,

I have an issue in my institution. I can't browse my iTunes U content, especially videos. Videos never start and also block iTunes 30 seconds later.

Do you know which ports need to be open ? My institution is behing a very narrow firewall, we also use a proxy (which is well configurated I guess).

I've been told that 80 and 443 ports should be open (http and https) but it doesn't help, videos are not launching.

Are there other ports to be open ?

Thanks for your help.