Should FaceTime work without a defined Proxy Server on restricted networks? We are having some problems with FaceTime video calling on our network where some traffic is restricted and firewalled from going out to the internet. 

In order for the iPads on the wireless network to connect to the Internet, a Proxy Server needs to be configured on the iPad.

Upon making that change, the user can then browse to google.com etc within mobile Safari. Without the Proxy Server set the user can no longer access external webpages within mobile Safari.

However FaceTime works regardless of whether the Proxy Server is set. A faceTime call is initiated from 2 seperate wireless connections.

The network configuration here allows users to ping google.com for example regardless of whether a Proxy Server is defined.

So.... should FaceTime work without a Proxy and if it does, how does it work?
This depends on the limitations you have in your network. If you're only limiting HTTP traffic and forcing the clients to go through a web proxy, then you're probably not cutting off FaceTime's custom TCP and UDP connections.

The exact protocol for FaceTime hasn't been released to public by Apple, but they do publish a guideline regarding network configuration (open ports) needed for FaceTime and iMessage: http://support.apple.com/kb/HT4245