ISA Server 2004 does not provide an H.323 gatekeeper. However, ISA Server 2004 does provide an H.323 filter.
An H.323 gatekeeper was included in ISA Server 2000. If you have installed an H.323 gatekeeper in ISA Server 2000, the H.323 gatekeeper is removed when you upgrade to Internet Security and Acceleration Server 2004. If you require an H.323 gatekeeper on your network, you must install the gatekeeper on another computer.
The H.323 protocol filter that is provided with ISA Server 2004 is an application filter for the H.323 protocol. Application filters are ISA Server extensions that examine or modify application data, such as SMTP, H.323, and streaming media. The H.323 protocol filter is used by client-to-client audio-visual applications to allow conferencing applications, such as Microsoft NetMeeting 3.0 and later, to work through ISA Server.
For more information about H.323, visit the Understanding the H.323 Standard
Web page on the Microsoft TechNet Web site: