h323plus  1_27_0
About: H.323 Plus offers libraries for voice (VoIP) and videoconferencing using H.323.
  Fossies Dox: h323plus-1_27_0.tar.gz  ("inofficial" and yet experimental doxygen-generated source code documentation)  


Table of Contents


H323Plus is an Open Source class library for the development of applications using the H.323 protocol for multi-media communications over packet based networks. It continues the development of OpenH323 under the old API. It uses the PTLib library to provide platform independence, and makes extensive use of the C++ techniques of inheritance and polymorphism.

This document is intended as reference guide, not a tutorial. For examples of using H323Plus, see the sample programs provided in the samples directory. A tutorial on using PTLib and OpenH323/H323Plus is also available at http://toncar.cz/openh323/tut/ .

Last updated 19 January, 2010

Copyright (C) 1999-2003 Equivalence Pty Ltd, All right reserved

Portions Copyright (C) 2004 Post Increment, All Rights Reserved


The fundamental object in the ownership hierarchy is the H323Endpoint class. An application would typically have one instance of a descendant of this class. The application defined descendant would set up defaults for various H323 parameters (timeouts etc), the most important of which is the capability table which defines the codecs and channel types the application is capable of handling.

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.

Class hierarchy

H323Plus provides a rich class hierarchy that allows access to most of the functions requires for H.323 endponts. The list below is not intended an exhaustive list of the classes available (which is available here) but is good starting point for finding out more information on the various functions available

Endpoint Classes

  • H323EndPoint - implements a H.323 endpoint that can make or receive calls
  • H323Connection - an instance of the class is created for each outgoing or incoming call
  • H323Channel - the base class for all H.323 logical channels
  • H323Codec - the base class for all codecs. See also H323AudioCode and H323VideoCodec
  • H323SignalPDU - the base class for all H.323 Protocol Data Units (PDU)
  • H323DataPDU - the base class for all H.323 Protocol Data Units (PDU)
  • H323GatekeeperServer - implements a H.323 Gatekeeper, i.e. a server for H.225 RAS protocl

Data types

H.225 Protocol Classes

These classes are created from the H.225 ASN definitions

H.245 Protocol Classes

These classes are created from the H.245 ASN definitions


  • 17 May 2004 - Converted from Doc++ to Doxygen format by Craig Southeren
  • 19 January 2010 - Minor updates for H323Plus by Jan Willamowius