"Application Inspection" is also known as "Fixup".The fixup protocol h323 command provides support for H.323-compliant endpoints. PIX Firewall Version 5.3 through Version 6.2 supports H.323 Version 2. PIX Firewall Version 6.3 supports H.323 Version 3 and Version 4.
H.323 is a suite of protocols defined by the International Telecommunication Union (ITU) for multimedia conferences over LANs. H.323 supports VoIP gateways and VoIP gatekeepers. H.323 Version 2 adds the following functionality:
"Fast Connect or Fast Start Procedure for faster call setup
"H.245 tunneling for resource conservation, call synchronization, and reduced set up time