| 12.2 |  | Multimedia Support |
| 12.2.3 |  | H.323 |

| The H.323 standard was developed by the International Telecommunication Union for carrying multimedia applications over IP. H.323 is an umbrella protocol that supports a number of other protocols and standards. These include the following:

- H.225 Registration, Admission, and Status (RAS)
- H.225 Call Signaling
- H.245 Control Signaling
- TPKT Header
- Q.931 Messages
- ASN.1 for PIX Security Appliance 5.2

H.323 is more complicated than other traditional protocols because it uses two TCP connections and several UDP sessions for a single call. Only one of the TCP connections goes to the well-known port 1720. The other TCP and all of the UDP ports are negotiated and are temporary. Furthermore, the content of the streams is far more difficult for firewalls to understand than existing protocols because H.323 encodes packets using Abstract Syntax Notation (ASN).

Currently, the PIX Security Appliance supports H.323 versions 1 and 2. However, only PIX Security Appliance software versions 5.2 and higher support version 2. While both versions support H.323 VoIP gateways and VoIP gatekeepers, version 2 adds the following functionalities to the PIX Security Appliance:

- Fast Connect or Fast Start Procedure for faster call setup
- H.245 tunneling for resource conservation, call synchronization, and reduced set up time

Supported H.323 applications include the following:

- Cisco Multimedia Conference Manager
- Microsoft NetMeeting
- Intel Video Phone and InternetPhone
- CUseeMe Network MeetingPoint and CuseeMe Pro
- VocalTec Internet Phone and Gatekeeper

The fixup protocol h323 command and its syntax are explored in the Command Reference.