This document is intended as reference guide, not a tutorial. For examples of using OpenH323, see the sample programs provided in the samples directory. A tutorial on using PWLib and OpenH323 is also available at http://toncar.cz/openh323/tut.
Last updated 17 May, 2004
Copyright (C) 1999-2003 Equivalence Pty Ltd, All right reserved
Portions Copyright (C) 2004 Post Increment, All Rights Reserved
Also created by the application in the H323Endpoint would be instances of one or more descendants of the H323Listener class. There is a descendant of this class for each protocol that is supported. For example H323ListenerIP would be for Internet use. Each listener spawns a thread that monitors its protocol and when a new incoming call is detected, creates an instance of a H323Transport class descendent. As for the H323Listener class, there is a descendent for each protocol supported, eg H323TransportIP.
When the first PDU arrives on a H323Transport using the Q.931 and H.225 protocols, there is a call reference that identifies the connection that has been made. These connections are embodied by the H323Connection class, which contains all of the state information for a connection between H323 endpoints. The H323Endpoint instance keeps track of these active connections. If there is no connection for the call reference number already, a new one is created and H323 signalling negotiations begun.
An application would often have the system create an instance of a descendant of the H323Connection class, rather than that class itself. This is so that any of a large number of virtual methods may be overridden. These virtual methods are "callback" functions by the library to allow the application to either obtain information or modify the behaviour at various phases of the protocol negotiations. For example, there is a callback for when an incoming call is in progress and the application user should be "alerted". This is highly application specific being anything from a simple audible beep to displaying a pop up window with bells and whistles.
The H323Negotiator classes are used to maintain the state and functionality of each command or variable defined by the H.245 protocol. Their main reason for existence is actually to reduce the scope of the h225.h and h245.h files, which define many hundreds of classes. A user of the H323Connection class thus does not have to include all of these classes on every compilation unit.
During some of the H.245 negotiations, logical channels may be created, both by the remote endpoint and by the local application. The H323Channel class descendants represents this. A typical use of one of these classes is to open a stream of encoded audio data. The H323Channel class would create a H323Codec using the H323Capability that was passed during the protocol negotiations.
1.4.7