A. App-V has a number of options for application streaming, including HTTP, but the primary protocol is RTSP, which operates over port 554 (or 322 when SSL is used with it, RTSPS).
The easiest way to test if RTSP is functioning is to telnet to port 554t on your server. After you press Enter a few times, you should get a response similar to the one below. If you don't, check your configuration and that the Application Virtualization Management Server service is running.
If I enter the command
telnet savdalappv01 554
I would see
RTSP/1.0 400 Bad Request
Server: Microsoft Application Virtualization Server/184.108.40.20640 \\[Win32; Windows
Date: Sat, 27 Feb 2010 21:56:24 GMT>
Connection to host lost.