# H323 Protocol Agent

H.323 defines a set of protocols as well as the components and procedures for real-time multimedia communication.

H.323 consists of a series of different types of standards related to video and audio services, real-time transport, control channels, and security.

On Firewalls, this Protocol Agent has parameters you can set in the Service properties:

- H.323 can open several related connections, which places demands on access control and NAT. The H323 Protocol Agent’s task is to track the related connections that are opened within the same session. Particularly, if you want the Firewall to apply NAT to H.323 connections, you must make sure that the connections use this Protocol Agent.
- The H323 Protocol Agent examines Call Signaling Channel (Q.931/H.225.0) connections and allows the related Control Channel (H.245) connection to open. It also examines the H.245 connection and allows further related connections (RTP and RTCP) to open, based on the port negotiations on the parent connection.
- When NAT is applied to Q.931 connections, the Protocol Agent performs the same NAT to the related H.245 connection and changes the payload data of the parent connection. The same NAT operation is performed also on the opened RTP and RTCP connections.

There are no configurable parameters for this Protocol Agent on IPS engines or Layer 2 Firewalls.