Ankit,
If you're looking for FAST data but you only see the "Data" bytes (not "FAST"), then you may only need to assign a port for the plugin to listen for FAST data. Navigate to Edit > Preferences > Protocols > FAST, then set the port number to the one on which you expect FAST traffic.
If the FAST protocol preferences don't exist at all, the plugin is not properly installed.
I can't think of any other causes at the moment. Hopefully that suggestion works!
-- Alex