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h323plus.dox
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/*! \mainpage H323Plus
\section contents Table of Contents
\li \ref intro
\li \ref arch
\li \ref sec
\li \ref classes
\li \ref history
\section intro Introduction
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 29 July, 2021
Copyright (C) 1999-2003 Equivalence Pty Ltd, All right reserved
Portions Copyright (C) 2004 Post Increment, All Rights Reserved
\section arch Architecture
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.
\section sec Security note
If you use the H.263 or H.264 video plugin, you need to make sure that no attacker can
manipulate the environment variables they see since environment variables are used to
find and load shared libraries.
\section classes Class hierarchy
H323Plus provides a rich class hierarchy that allows access to most of the functions
requires for H.323 endpoints. 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
\subsection endpoint Endpoint Classes
\li H323EndPoint - implements a H.323 endpoint that can make or receive calls
\li H323Connection - an instance of the class is created for each outgoing or incoming call
\li H323Channel - the base class for all H.323 logical channels
\li H323Codec - the base class for all codecs. See also H323AudioCode and H323VideoCodec
\li H323SignalPDU - the base class for all H.323 Protocol Data Units (PDU)
\li H323DataPDU - the base class for all H.323 Protocol Data Units (PDU)
\li H323GatekeeperServer - implements a H.323 Gatekeeper, i.e. a server for H.225 RAS protocol
\subsection daattypes Data types
\li H225_AliasAddress - defines a H.225 aliasAddress object
\li H323TransportAddress - defines a IPv4 or IPv6 transport address as a string
\subsection h225 H.225 Protocol Classes
These classes are created from the H.225 ASN definitions
\li H225_Setup_UUIE
\li H225_CallProceeding_UUIE
\li H225_Connect_UUIE
\li H225_Alerting_UUIE
\li H225_Information_UUIE
\li H225_ReleaseComplete_UUIE
\li H225_Facility_UUIE
\li H225_Progress_UUIE
\li H225_Status_UUIE
\li H225_StatusInquiry_UUIE
\li H225_SetupAcknowledge_UUIE
\li H225_Notify_UUIE
\li H225_GatekeeperRequest,
\li H225_GatekeeperConfirm,
\li H225_GatekeeperReject,
\li H225_RegistrationRequest,
\li H225_RegistrationConfirm,
\li H225_RegistrationReject,
\li H225_UnregistrationRequest,
\li H225_UnregistrationConfirm,
\li H225_UnregistrationReject,
\li H225_AdmissionRequest,
\li H225_AdmissionConfirm,
\li H225_AdmissionReject,
\li H225_BandwidthRequest,
\li H225_BandwidthConfirm,
\li H225_BandwidthReject,
\li H225_DisengageRequest,
\li H225_DisengageConfirm,
\li H225_DisengageReject,
\li H225_LocationRequest,
\li H225_LocationConfirm,
\li H225_LocationReject,
\li H225_InfoRequest,
\li H225_InfoRequestResponse,
\li H225_NonStandardMessage,
\li H225_UnknownMessageResponse,
\li H225_RequestInProgress,
\li H225_ResourcesAvailableIndicate,
\li H225_ResourcesAvailableConfirm,
\li H225_InfoRequestAck,
\li H225_InfoRequestNak,
\li H225_ServiceControlIndication,
\li H225_ServiceControlResponse,
\subsection h245 H.245 Protocol Classes
These classes are created from the H.245 ASN definitions
\li H245_NonStandardMessage
\li H245_MasterSlaveDetermination
\li H245_TerminalCapabilitySet
\li H245_OpenLogicalChannel
\li H245_CloseLogicalChannel
\li H245_RequestChannelClose
\li H245_MultiplexEntrySend
\li H245_RequestMultiplexEntry
\li H245_RequestMode
\li H245_RoundTripDelayRequest
\li H245_MaintenanceLoopRequest
\li H245_CommunicationModeRequest
\li H245_ConferenceRequest
\li H245_MultilinkRequest
\li H245_LogicalChannelRateRequest
\li H245_MasterSlaveDeterminationAck
\li H245_MasterSlaveDeterminationReject
\li H245_TerminalCapabilitySetAck
\li H245_TerminalCapabilitySetReject
\li H245_OpenLogicalChannelAck
\li H245_OpenLogicalChannelReject
\li H245_CloseLogicalChannelAck
\li H245_RequestChannelCloseAck
\li H245_RequestChannelCloseReject
\li H245_MultiplexEntrySendAck
\li H245_MultiplexEntrySendReject
\li H245_RequestMultiplexEntryAck
\li H245_RequestMultiplexEntryReject
\li H245_RequestModeAck
\li H245_RequestModeReject
\li H245_RoundTripDelayResponse
\li H245_MaintenanceLoopAck
\li H245_MaintenanceLoopReject
\li H245_CommunicationModeResponse
\li H245_ConferenceResponse
\li H245_MultilinkResponse
\li H245_LogicalChannelRateAcknowledge
\li H245_LogicalChannelRateReject
\li H245_MaintenanceLoopOffCommand
\li H245_SendTerminalCapabilitySet
\li H245_EncryptionCommand
\li H245_FlowControlCommand
\li H245_EndSessionCommand
\li H245_MiscellaneousCommand
\li H245_CommunicationModeCommand
\li H245_ConferenceCommand
\li H245_H223MultiplexReconfiguration
\li H245_NewATMVCCommand
\li H245_MobileMultilinkReconfigurationCommand
\li H245_FunctionNotUnderstood
\li H245_MasterSlaveDeterminationRelease
\li H245_TerminalCapabilitySetRelease
\li H245_OpenLogicalChannelConfirm
\li H245_RequestChannelCloseRelease
\li H245_MultiplexEntrySendRelease
\li H245_RequestMultiplexEntryRelease
\li H245_RequestModeRelease
\li H245_MiscellaneousIndication
\li H245_JitterIndication
\li H245_H223SkewIndication
\li H245_NewATMVCIndication
\li H245_UserInputIndication
\li H245_H2250MaximumSkewIndication
\li H245_MCLocationIndication
\li H245_ConferenceIndication
\li H245_VendorIdentification
\li H245_FunctionNotSupported
\li H245_MultilinkIndication
\li H245_LogicalChannelRateRelease
\li H245_FlowControlIndication
\li H245_MobileMultilinkReconfigurationIndication
\subsection history History
\li 17 May 2004 - Converted from Doc++ to Doxygen format by Craig Southeren
\li 19 January 2010 - Minor updates for H323Plus by Jan Willamowius
*/