Inbound and outbound UDP for the data traffic. Each track in a movie uses a pair of UDP ports (even/odd number). The RTP traffic flows on the even port, from server to client (no back traffic). RTCP traffic flows on the odd port, both ways. QuickTime uses ports 6970 and up on the client side, servers vary widely. Opening, say, 30 ports here should allow any client to view several movies and not run out.