If you submit an iOS ipa file via Apple's Application Loader and see the activity gets stuck at the TCP/UDP connectivity testing step. It may be because your current network is blocked by firewall. An easy solution but may be hard to find is to change the Delivery mechanism option in the Application Loader's Preferences.
Uncheck 'Signiant' and 'Aspera' will force the loader to use DAV SSL port 443. It worked for me.