Abstract:
In a computer system having a memory, a processor, and a network interface, a method for listening on multiple conferencing interfaces having the steps of loading a set of transport components into the memory; initializing each transport components of the set of transport components to listen on a particular conferencing interface using the network interface, each transport component of the set of transport components listening to a different conferencing interface; receiving an incoming call signal on the network interface having an incoming conferencing interface; processing the incoming call signal to detect the incoming conferencing interface; and launching an application based on the incoming conferencing interface. 
     An apparatus for listening on multiple conferencing interfaces having a set of transport components coupled to the network interface, each transport component of the set of transport components having the capability of receiving a signal on a different conferencing interface; a conference component coupled to each component in the set of transport components; a call processing module coupled to the conference component; and, a process manager coupled to the call processing module; the conference component containing a circuit for causing the call processing module to cause process manager to activate a conferencing application upon detecting a call from one transport component of the set of transport components.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the field of use of teleconferencing systems. More particularly, the present invention relates to the dynamic launching of teleconferencing applications upon receipt of a call. 
     2. Description of Related Art 
     Teleconferencing is increasingly becoming a popular application in personal computer systems. Such applications typically allow the transfer of audio and video data between users so that they can speak and otherwise communicate with one another. Such applications sometimes also include data sharing wherein various types of data such as documents, spreadsheets, graphic data, or other types of data, can be shared and manipulated by all participants in the teleconference. Different teleconference applications perhaps residing on different hardware platforms have different capabilities. Moreover, a wide variety of features has been implemented in different teleconference applications, and the proliferation of different types of computer systems with different capacities, and different networking media has created challenges for teleconferencing. 
     For example, most systems which are used for teleconferencing applications are also used to run such programs for performing word processing, spreadsheet applications, database applications, and a variety of other applications. Thus, the resources contained in the computer system are shared between these multiple applications. Often, most computer systems are limited in the amount of random access memory they contain and also the amount of processing power available for performing operations. In order for a user to receive calls, the user must keep the conferencing application open. Otherwise, if the called party does not have the conferencing application open, the calling party would receive a notice that the called party is not present to answer the call. 
     So, in order to receive a call, a user currently needs to keep any conferencing application open. However, keeping the conferencing application open is a waste of resources. Memory which is allocated to the conferencing application could be used for other applications. Also, processing resources are consumed in launching and maintaining the conferencing application. These resources are unnecessarily preoccupied for the times when there are no teleconferencing sessions in occurrence. A user can wait until he wishes to initiate a teleconferencing session before launching the teleconferencing application, but this means that there is no call notification unless the user receives a “regular” phone call, which does not allow for on-demand conferencing. 
     Thus, a solution needs to be provided that will allow a system to dynamically load the conferencing application only when necessary to answer a call, but not require the conferencing application to be loaded and executing to receive notice of an incoming call. 
     In addition, a solution should be provided that will allow a conferencing application to wait on incoming calls on various ports simultaneously, thereby allowing a conferencing application which can handle conferencing over several different network/conferencing protocols and/or interfaces to achieve parallel conferencing capabilities (i.e., answering multiple calls, each coming in on a different network protocol or a different conferencing interface). 
     Moreover, a solution needs to be provided for multiple conferencing applications, each compatible with a different set of network/conferencing protocols, to be able to listen for incoming calls at the same time. 
     SUMMARY OF THE INVENTION 
     The invention provides a method and apparatus for listening on multiple network/conferencing protocols and/or interfaces. In addition, multiple persistent listening for multiple ports can exist for multiple conferencing applications (i.e., one persistent listen to one conferencing application) AND for a single conferencing application (i.e., multiple persistent listen to one conferencing application). Thus, for example a conferencing application can listen for incoming calls on both a TCP/IP port or an AppleTalkl™ port. 
     The invention can be implemented in a computer system having a memory, a processor, and a network interface, a method for dynamically launching a conferencing application upon the receipt of an incoming call comprising the steps of loading a set of transport components into the memory; initializing each transport components of the set of transport component to listen on a particular conferencing interface using the network interface, each transport component of the set of transport components listening to a different conferencing interface; receiving an incoming call signal on the network interface having an incoming conferencing interface; processing the incoming call signal to detect the incoming conferencing interface; and launching an application based on the incoming conferencing interface. 
     An apparatus including a set of transport components coupled to the network interface, each transport component of the set of transport components having the capability of receiving a signal on a different conferencing interface; a conference component coupled to each component in the set of transport components; a call processing module coupled to the conference component; and, a process manager coupled to the call processing module; the conference component containing a circuit for causing the call processing module to cause process manager to activate a conferencing application upon detecting a call from one transport component of the set of transport components. 
     The invention will allow a system to dynamically load a conferencing application only when necessary to answer a call, but not require the conferencing application to be loaded and executing to receive notice of an incoming call. In addition, different conferencing applications can also be “dynamically” launched when incoming calls corresponding to each different conferencing applications arrive. 
     Other objects, features and advantages of the invention will be apparent from the accompanying drawings, and from the detailed description that follows below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates an example configuration in which various embodiments of the invention may be implemented. 
     FIG. 2 illustrates a single system in which embodiments of the invention may be implemented. 
     FIG. 3 illustrates an example architecture on which a system employing various embodiments of the invention is based. 
     FIG. 4 illustrates a preferences file configured in accordance to the invention. 
     FIG. 5 illustrates a system employing various embodiments of the invention. 
     FIG. 6 illustrates a system employing various embodiments of the invention used for initializing persistent listening. 
     FIG. 7 illustrates a system employing various embodiments of the invention used for transfering an incoming call. 
     FIG. 8 is a flow diagram illustrating a prefered operation of the invention used for dynamically launching a conferencing application. 
     FIG. 9 illustrates a system employing various embodiments of the invention used for initializing a second persistent listening. 
     FIG. 10 illustrates a system employing various embodiments of the invention used for maintaining a second persistent listening on a second port. 
     FIG. 11 illustrates a system employing various embodiments of the invention used for receiving an incoming call on a first port. 
     FIG. 12 illustrates a system employing various embodiments of the invention used for receiving an incoming call on the second port while a call is received on a first port. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides a method and apparatus for dynamically launching teleconferencing applications upon receipt of a call. For purposes of explanation, specific embodiments are set forth to provide a thorough understanding of the present invention. However, it will be understood by one skilled in the art, from reading this disclosure, that the invention may be practiced without these details. Further, although the present invention is described through the use of certain specific embodiments thereof, especially, with relation to certain hardware configurations, data structures, packets, method steps, and other specific details, these should not be viewed as limiting the present invention. Various modifications can be made by one skilled in the art, without departing from the overall spirit and scope of the present invention. 
     A portion of the disclosure of this patent document contains material which is subject to copyright protection. They copyright owner has no objection to the facsimile reproduction by anyone of the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever. Copyright Apple Computer, Inc. 
     A typical system configuration in which a teleconference may take place is illustrated as  100  in FIG.  1 . For example, a first workstation  150  may communicate via teleconference with a second workstation  155 , as illustrated. System  150  may include a central processing unit  150   c  which is coupled to a display  150   d  a video input device  150   a , and a sound input device  150   b . The system  150  may communicate with over system  155  over networking medium  170  via network connection module  160 . Network connection module  160  may include any number of network adapters commercially available such as Ethernet, Token Ring, or any other networking standard commercially available. Note that network adapter  160  may also include a wireless network adapter which allows transmission of data between components without a medium  170 . Communication is thus provided via network adapter  165  coupled to system  155 , and bi-directional communications may be established between two systems. System  150  further has a keyboard  150   e  and a pointing device  150   f , such as a mouse, track ball, or other device for allowing user selections and user input. 
     In implemented embodiments of the present invention, a general purpose computer system is used for implementing the teleconferencing applications and associated processes to be described here. Although certain of the concepts to be described here will be discussed with reference to teleconferencing, it is apparent that the methods and associated apparatus can be implemented for other applications, such as file sharing, real time data acquisition, or other types of applications which sends data from a first participant to a second participant or set of participants. A computer system such as that used for implementing embodiments of the present invention will now be described. 
     FIG. 2 is a diagram showing a computer system capable of implementing the present invention, such as a workstation, personal computer or other processing apparatus. The sub-system  300  comprises a bus or other communication means  301  for communicating information, and a processor  302  coupled with bus  301  for processing information. Sub-system  300  further comprises a random access memory (RAM) or other volatile storage device  304  (referred to as main memory), coupled to bus  301  for storing information and instructions to be executed by processor  302 . Main memory  304  also may be used for storing temporary variables or other intermediate information during execution of instructions by processor  302 . Sub-system  300  also comprises a read only memory (ROM) and/or other static storage device  306  coupled to bus  301  for storing static information and instructions for processor  302 , and a mass storage device  307  such as a magnetic disk or optical disk and its corresponding disk drive. Mass storage device  307  is coupled to bus  301  for storing information and instructions. 
     Sub-system  300  may further be coupled to a display  321  such as a cathode ray tube (CRT) or liquid crystal display (LCD) coupled to bus  301  for displaying information to a computer user. Such a display  321  may further be coupled to bus  301  for the receipt of video or image information. A keyboard  322 , including alphanumeric and other keys may also be coupled to bus  301  for communicating information and command selections to processor  302 . An additional user input device is cursor control  323 , such as a mouse, a trackball, stylus, or cursor direction keys, coupled to bus  301  for communicating direction information and command selections to processor  302 , and for controlling cursor movement on display  321 . For teleconferencing applications, system  300  may also have coupled to it a sound output device  328 , a video input device  329 , and sound input device  326 , along with the associated D/A (Digital-to-Analog) and A/D (Analog-to-Digital) converters or software codecs for inputting or outputting media signal bitstreams. System  150   c  may further be coupled to communication device  327  which is coupled to network adapter  160  for communicating with other computers over network  370 . 
     Note, also, that any or all of the components of system  150   c  and associated hardware may be used in various embodiments, however, it can be appreciated that any configuration of the system may be used for various purposes according to the particular implementation. 
     In one embodiment, system  300  is one of the Apple Computer® brand family of personal computers such as the Macintosh 8100 brand personal computer manufactured by Apple Computer, Inc. of Cupertino, Calif. Processor  302  may be one of the PowerPC brand microprocessors manufactured by Motorola, Inc. of Schaumburg, Ill. 
     Although a general purpose computer system has been described, it can be appreciated by one skilled in the art, however, that the following methods and apparatus may be implemented in special purpose hardware devices, such as discrete logic devices, large scale integrated circuits (LSI&#39;s), application-specific integrated circuits (ASIC&#39;s), or other specialized hardware. The description here has equal application to apparatus having similar function. 
     FIG. 3 illustrates a plurality of processes and/or apparatus which may be operative within system  150   c . At the highest level, for example, at the highest level in the ISO/OSI networking model, a conferencing application  401 , such as a teleconferencing application, an audio/video server, or a data server, communicates with a conference component  400  in the form of Application Program Interface (API) calls. 
     Conference component  400  allows conferencing application  401  to establish communications between two or more teleconference stations. Control information, and media information can be transmitted between the first participant system and a second participant system. Conference component  400  communicates with the transport component  402  by sending messages for other teleconferencing stations which are encapsulated and placed into a form that the transport component  402 , and the network component  403 , can packetize and transmit over networking medium  170 . 
     Transport component  402  and networking component  403  provide the necessary operations for communication over the particular type of network adapter  160  and networking medium  170  according to a particular implementation. For example, networking component  403  may provide the TCP or ADSP protocols and packetizing, according to those respective standards. Transport component  402  can support standards such as H.320 or MovieTalk™ transport standards. There can exist multiple transport components and multiple network components, as described below. 
     The main function of conference component  400  is to establish and maintain a bi-directional connection between every member of a conference—i.e., between conferencing applications. Conferencing applications use a control channel to exchange control data that is pertinent to the conference. This data might include user identification information or other information that is germane to the application&#39;s operation. Conferencing applications (e.g., conferencing applications  401 ) define the format and content of these control messages by establishing their own control protocols within the boundaries of the conferencing API. Conferencing components further establish communication channels between a first endpoint and a second endpoint, using underlying transport component  402 . Thus, once a media channel has been established, conference component  400  uses the media channel of transport component  402  which is provided for transmission of media and non-media information. 
     Conferencing application  401  controls conference component  400  by the issuance of QuickTime™ Conferencing API calls. Conferencing applications operate using an event-driven model wherein events pertinent to the application are issued to conferencing application  401 . Conferencing application  401  can then take appropriate action either by modifying internal data structures within (creating a source or sync), and/or issuance of appropriate messages over the network to other connected components, or potential participants. In addition, conference components also respond to events and messages that are received. In addition, conference components take appropriate actions pertaining to the receipt of API calls from conferencing applications. 
     There can exist multiple conferencing components, wherein each conferencing application requires at least one conference component, but each conferencing application can have more than one associated conference component. Each conferencing component has an unique identification number. In addition, each conference component contains one “listen string”, which is unique. A listen string is the encapsulation of the parameters of the “MTConferenceListen” API call for each conference component. Listen strings can contain more than one network or port. A listen string is composed of two parts: a fixed portion identifying a service name (which is similar to service names given to printers in an AppleTalk™ network that are displayed in the Chooser application in the Apple Macintosh operating system), and a variable portion containing a list of one or more service types, which contain the transport/network types with which the transport components and network components can interface. For example, service types can be port numbers for TCP/IP networks or device types for AppleTalk network. The transport/network tuples will be described below in association with the discussion of FIG.  5 . 
     The system as shown in FIG. 3 requires that a conferencing application  401  be present to handle incoming call events generated by conference component  400 . As conferencing applications (such as conferencing application  401 ) utilize significant system resources (e.g., processor processing power and memory space), the requirement that conferencing application  401  be executing even when there are no calls present to necessitate the existence of a conferencing application prevents the use of those resources by other applications. A system that removes the requirement by allowing conferencing application  401  to be launched when needed (i.e., launching only when there is an incoming call to handle), is described below. 
     FIG. 5 illustrates a preferred embodiment of the invention having a call director  502 ; a demon conference component  504  (i.e., a conference component acting in demon mode); a transport component  506 ; and a network component  508 . The preferred embodiment also contains a call director preferences  510 . Call director  502 , demon conference component  504 , transport component  506 , and network component  508  can be referred to as call processing module. 
     Call director  502  is a “faceless” background process that is loaded at initialization of the computer system contained in FIG.  2 . One of the main functions of call director  502  is to initiate the automatic launching of a conferencing application when a call is received by the computer system. In addition, call director  502  is responsible for initiating and interacting with demon conference component  504  to control the transfer of calls to a conferencing application. As a faceless process—i.e., a process that does not need to contain any code to interface directly with a user—call director  502  requires very little in terms of system resources. More importantly, aside from the indications given by the dynamic launching capabilities and other functionality provided by call director  502 , and the relatively small memory foot-print of call director  502 , the user does not even have to be aware that call director  502  is existent. Through the use of the elements contained in FIG. 5, conferencing application  401  does not have to be loaded and executing until an incoming call exists. 
     Demon conference component  504 , which is controlled by call director  502  through the use of the QuickTime™ Conferencing Application API, is responsible for performing the persistent listening for incoming calls. Demon conference component  504  is created by call director  504  after call director  504  has finished launching. Demon conference component  504  is an instance of the class of conference components that is initiated into a special mode of operation by call direction  504  through the use of a “MTConferenceSetPersistence” API call with the parameter “mtPersistenceDemonMode”. 
     In a preferred embodiment, there can only be one demon conference component in each computer system. Demon conference component  504  is the only conference component instance of call director  502 . That is, call director  502  can only have a single instance of a conference component (as opposed to conferencing application, which can have multiple conference component instances). Demon conference component  504  communicates with other conference components to transfer incoming calls indicated by transport component  506  and network component  508  using a shared data structure in memory. A preferred embodiment of the shared data structure is further described below, along with a description of the basic operations of the invention, while referencing FIG.  6 . 
     FIG. 6 illustrates a sample configuration using the preferred embodiment of the invention wherein conferencing application  401  and conference component  400  interacts with call director  502  and demon conference component  504  through the use of a shared queue structure  512 . 
     Inter-Conference Component Communication 
     In the preferred embodiment, conference components communicate (i.e., achieve interprocess communication) through the use of shared memory. Specifically, conference components communicate through the use of globally accessible data structures composed of a demon queue and an application queue, both of which are contained in shared queue structure  512 . The demon queue is used by any conferencing component of a conferencing application to send commands and information to demon conferencing component  504  (“QdPersistenceOn”, “QdPersistenceOff”, “QdListenAgain”, “QdPersistenceClear”). The application queue is used by the demon conferencing component to send messages to other conferencing components (“QdListenerStatus”, “QdDemonOff”, “QdIncomingCall”). It is to be noted that the choice of using queues to allow inter-component communication is not intended to be limiting, and other methods of allowing inter-component communication can be used to achieve the same functionality. For example, instead of using queues to transfer commands and information, messages can be passed from one conferencing component to another. Alternatively, registers may be used to pass information from one conference component to another. 
     In the following description of FIG. 6, it is assumed that call director  502  has been loaded at the time of initialization of the computer system, and call director  502  has created an instance of the class of conference components and initialized into that conference component instance into demon conference component  504  through the use of the “MTConferenceSetPersistence” API call with a parameter of “mtPersistenceDemonMode”. It is important that a demon conference component such as demon conference component  504  exists so as to perform persistent listening. If there is not a conference component in demon mode, there can be no persistent listening. Moreover, if a conferencing application tries to turn on persistent listening when there is no demon conference component initiated, the conference component of the conferencing application will return a “mtDemonKaputErr” message, indicating that there is no demon conference component to turn-on persistent listening. 
     Setting-Up Persistent Listening 
     As stated above, demon conference component  504  is responsible for listening for incoming calls on behalf of all conferencing applications that request persistent listening. Call director  502  is responsible for dynamically launching (if necessary) and transferring an incoming call to the conferencing application which requested persistent listening. The process for configuring demon conference component  504  and call director  502  in the preferred embodiment is as follows: 
     (1) conferencing application  401  will first send an “MTConferenceSetPersistence” API command with an “mtPersistenceOnMode” parameter after being launched to conference component  400 ; 
     (2) conference application  401  will then send an API command (“MTConferenceListen”) requesting persistent listening and passing a listen string, which includes the identification of the port on which it wishes demon conference component  504  to listen, to conferencing component  400 ; 
     (3) conference component  400  will place a request (QdPersistenceOn) on the demon queue to have demon conference component  504  perform persistent listening on the port specified by conferencing application  401  (the request containing an application signature, as discussed below, identifying conferencing application  401  as the requester and the parameters, or so-called “listen string”, of the listening that conferencing application  401  is requesting, the parameters including a service name and a port); 
     (4) demon conference component  504  will initialize transport component  506  and network component  508  as necessary to perform persistent listening on the requested service type and port; 
     (5) at substantially the same time as step (4), demon conference component  504  will also notify call director  502  through the use of a “mtPersistenceChangedEvent” that conferencing application  401  has requested persistent listening, and send the application signature of conferencing application  401  and the listen string, which, as stated, includes information regarding the service type and port on which conferencing application  401  wishes to listen; 
     (6) call director  502  will then store the information received from demon conference component  504 , including the application signature of conferencing application  401  (call director  502  will create an alias, as described below, for conferencing application  401  from the application signature), the service name, the transport type, the network type, and the service type into call director preferences  510 ; and, 
     (7) lastly, conferencing application  401  can either end execution or remain running—but under either case, the listening for incoming calls will be done by demon conference component  504 , as described below. 
     Persistent Listening of Incoming Calls 
     During normal operations, demon conference component  504 , after detecting an incoming call, will notify the conferencing application which requested the listening to transfer the incoming call. As mentioned above, in order to ensure that an incoming call can be matched-up with a conferencing application, call director  502  uses call director preferences  510  to track of the conferencing applications that requests persistent listening. Call director  502  also uses call director preferences  510  to track all listen strings of the various conference components corresponding to the various conferencing applications. Also as discussed above, each listen string corresponds to a particular conference component and contain the service and the ports for which that conference component is responsible. Thus, call director preferences  510  contains: (1) a list of aliases for conferencing applications that requested listening; and (2) what each conferencing applications want to listen on, such as the name of a user, the transport and the network type, and the service type (e.g., a port number for TCP/IP)). 
     FIG. 4 illustrates the contents of call director preferences  510 , displayed in content window  410 , containing logical representations of: a listen strings list  412  (“mtls”), and a conferencing application alias list  414  (“alis”). Call director  502  uses call director preferences  510  to keep track of the persistent listening requests of conferencing applications, and to hold the values used to initiate a demon conference components (e.g., demon conference component  504 ), any transport components (e.g., transport component  506 ), and any network components (e.g., network component  508 ). The contents of listen strings list  412  is displayed in a listen string list window  416 . The contents of conferencing application alias list  414  is displayed in alias list window  418 . 
     As can be seen in listen string list window  416 , only one listen string, a listen string  420 , is contained in listen strings list  412 . Listen string  420  is identified in listen string list  412  by the unique identification number “ 20556 ”, which is the identification number used to identify related resources in call director preferences  510 . In addition, in listen string list window  416 , it is shown that listen string  420  was initialized by conferencing application  401 , which in this example is entitled “QuickTime™ Web Conference”. Thus, listen string  420  identifies that conference component  400  belongs to conferencing application  401 . 
     The contents of listen string  420  is displayed in a listen string content window  422 . Listen string  420  contains a service name  424  (“James Watt” in ASCII and a hexadecimal equivalent), a transport type  426  (“mtlktcpi” in ASCII and a hexadecimal equivalent), and a port  428  (“ 458 ” in ASCII and a hexadecimal equivalent). Thus, conferencing component  401  is the requester of persistent listening for transport type  426  and port  428 . 
     Referring still to FIG. 4, a conferencing application alias  430  is shown in conferencing application alias list  414  in alias list window  418 . Conferencing application alias  422  has an identification number 20556, which is the same identification number used to identify listen string  420  in call director preferences  510 . Conferencing application alias  422  is used by call director  502  to locate and launch conferencing application  401  (i.e., QuickTime™ Web Conference) when an incoming call matches the profile contained in listen string  420 . The aliases contained in conferencing application alias list  414  is kept in call director preferences  510  and only used by call director  502 —i.e. aliases are never passed down to demon conference component  504 . 
     The contents of conferencing application alias  430  is shown in alias content window  432  and contains the location of conferencing application  401 . 
     Answering of Incoming Calls After Persistent Listening Has Been Activated 
     After persistent listening has been set-up, assuming that conferencing application is still running (see FIG.  6 ), when an incoming call is detected by transport component  506 , demon conference component  504  will transfer the incoming call to conferencing component  400 , which will notify conferencing application  401  of the incoming call. The incoming call is transferred through the following sequence: 
     (1) demon conference component  504  sends a “QdIncomingCall” message to conference component  400  through the use of shared queue structure  512 ; 
     (2) conference component  400  creates a new instance of a transport component and a new instance of a network component, which in FIG. 7 is transport component  402  and network component  403 , respectively; 
     (3) demon conference component  504  sends conference component  400  a reference to transport component  506 ; 
     (4) conference component  400  “answers” the call by sending a “MTTransportAnswer” message, along with the reference to transport component  506 , to transport component  402  instance to transfer the call from transport component  506 ; 
     (5) after the call has been transferred successfully, conference component  400  sends a “QdListenAgain” message to demon conference component  504  through the use of shared queue structure  512 ; and, 
     (6) demon conference component  504  issues a “TTransportListen” API call to transport component  506  to await the next incoming call. 
     System Re-Initialization After Persistent Listening has been Initialized 
     When the computer system is re-initialized and call director  502  is loaded and begins execution after system initialization, the following start-up sequence occurs: 
     (1) call director  502  reads call director preferences  510  and retrieves any listen strings; 
     (2) call director  502  initializes demon conference component  504  to place it into demon mode as described above; 
     (3) call director  502  sends one “MTConferenceDemonListen” API call to demon conference component  504  for each listen string that is retrieved from call director preferences  510 , where each API call passes demon conference component  504  the retrieved listen string and the associated application signature for the conferencing application that requested the listening. 
     Hi-jacking of Listening 
     A later conferencing application will replace the listening of conferencing application  401  if the later conferencing application wants to listen to the same port (under TCP/IP) or the same name/device (under AppleTalk). If this occurs, a “mtListenHijackedErr”, generated by demon conference component  504 , will be received by conference component  400  if conferencing application  401 , which has been “hi-jacked,” is still running. Conference component  400  will then inform conferencing application  401  that the listening requested by conference component  401  has been taken over so that conferencing application  401  can take any necessary action. 
     In addition, demon conference component  504  will send a “MTConferenceSetPersistence” API call with the parameter of “mtPersistenceOffMode”, along with the application signature of conferencing application  401 , to call director  502 . Call director  502  will then remove the listen strings for conferencing application  401  from call director preferences  510 . 
     If conferencing application  401  is not running when a hi-jack occurs, then the “mtListenHijackedErr” will be removed after a certain time. 
     Turning Off Persistent Listening 
     If persistent listening is turned off for a listen string (i.e., a conference component), there will be no notification of incoming calls for that listen string if the conferencing applications that handles that listen string is not loaded and executing—i.e., the system will operate as it had before the existence of the invention. However, the user will continue to receive notification of incoming calls on the listen strings for which persistent listening has not been turned off. 
     The sequence to turn off persistent listening will depend on whether conferencing application  401  is loaded and executing. If conferencing application  401  is loaded and executing, then the sequence is as follows: 
     (1) conferencing application  401  sends conference component  400  a request to turn off persistent listening via a “MTConferenceSetPersistence” API call with “mtPersistenceOffMode” parameter; 
     (2) conference component  400  sends a “QdPersistenceOff” message to demon conference component  504 ; 
     (3) demon conference component  504  will then remove transport component  506  and network component  508  and send a “QdDemonOff” message to conference component  400 ; 
     (4) demon conference component  504  sends a “MTPersistenceChangedEvent” message to call director  502  with the application signature for conferencing application  401 ; 
     (5) call director  502  removes the listen string for conference component  400  from call director preference  510 ; 
     (6) conference component  400 , after receiving the “QdPersistenceOff” message from demon conference component  504 , will create a new instance of a transport component and a new instance of a network component and initialize them for local listening—i.e. conference component  400  will be responsible for waiting for an incoming call for the listen string. 
     If the user thereafter quits conferencing application  401 , then the system will operate as if call director  502  is not present and the user will receive no notifications of incoming calls as conferencing application is not loaded and executed to perform listening. 
     It is to be noted that as a listen string can have more than one transport component and network component created for persistent listening—e.g., a listen string contains the listening for both a TCP/IP port and a AppleTalk service—demon conference component  504  will have to remove all the transport components and network components associated with the listen string for which persistent listening is turned off in step (3). In addition, when those instances of transport components and network components are removed, the conference component which requests that persistence listening be turned off for its listen string (e.g., conference component  400 ) will have to create a new set of transport component and network component instances to continue listening in step (6). 
     For a user to turn off persistent listening for the services and port that conferencing application  401  processes if conferencing application  401  is not currently loaded and executing, the user has to first launch conferencing application  401 . Conferencing application  401  then reads its own preference files and performs listen with same values as it did the last time it executed (i.e., conference component  400  sends a listen request with the same listen string it sent to initiate persistent listening to demon conference component  504 ). Then, the same sequence used to turn off persistent listening is used, as described above. 
     Dynamic Launching of a Conferencing Application 
     FIG. 8 is a flow diagram of the preferred operation of the invention wherein call director  502  operates to dynamically launch a conferencing application after persistent listening has been initialized and an incoming call is received. The system in operation at the start of the flow diagram is as shown in FIG.  5 . 
     In block  802 , call director  502  detects an incoming call through the use of demon conference component  504  and transport component  506 . Call director  502  is notified by an “mtIncomingCallForEvent”, containing an application signature of the conferencing application which set-up the listen string. 
     In block  804 , demon conferencing component  504  will place a “QdIncomingCall” message on the application queue with the application signature, listen string, identity of transport component  506  (i.e., a reference to transport component  506 ), and an “MTAddress” parameter, which identifies the address of the caller. Demon conference component  504  will also send an “MTIncomingCallForEvent” to call director  502  that an incoming call has been received along with an application signature and listen string for conferencing application  401  and conference component  400 . Call director  502  then checks the current process list to see if the conferencing application with the target application signature (i.e., conferencing application  401 ) is a process that is currently running. Operation will then continue with block  806 , as discussed below. If the conferencing application is not running, call director  502  will try to launch the conferencing application, as discussed in block  808 . 
     In block  808 , where the conferencing application is not currently executing, call director  502  will determine if the conferencing application is locatable so that it can be launched—i.e., whether the location of the conferencing application can be ascertained. Call director  502  will retrieve conferencing application alias  422  for conferencing application  401  from call director preferences  510 , update the location of conferencing application  401  if necessary, and then use the process manager to launch conferencing application  401 . If a conferencing application corresponding to conferencing application alias  422  cannot be found (e.g., where conferencing application  401  has been removed from the storage devices accessible to the computer system), then operations will continue with block  824 . 
     In block  810 , if conferencing application is locatable, call director  502  will determine whether there is enough free memory to run the conferencing application. If there is enough memory for conferencing application  401  to execute, call director  502  will then initiate the launching of conferencing application  401  continuing with block  812 . 
     If there does not exist enough memory for the conferencing application to execute, operations will continue with block  816 , where the user will be notified through an alert dialog that conferencing application  401  does not have enough memory to launch, and unless the user terminates and quits one or more processes that are currently occupying memory, the user will not be able to accept the incoming call. Call director  502  will keep checking for the user to free up memory until a predetermined time-out period has elapsed in block  818 . At the end of the time-out period, if the user has not freed-up enough memory, operation will continue with block  826 . If the user does free up enough memory, the operations will continue with block  812 . 
     In block  812 , where there exists enough memory for conferencing application  401  to begin execution, call director  502  will launch conferencing application  401  by using the process manager. Conferencing application  401  is notified that it must process the incoming call and therefore launches. 
     After conferencing application  401  has launched, the system configuration will be as shown in FIG. 6, where conferencing application  401  and its associated conference component  400  has loaded and is executing. 
     In block  814 , call director  502  checks to see if conferencing application  401  is listening in the same way as it was when the conferencing application set-up call director  502  for persistent listening. If conferencing application  401  does not listen in the same way within a reasonable time, demon conference component  504  recognizes that the incoming call has not been handled (i.e., the incoming call event has not been removed from the application queue) and will inform call director  502  with a “mtPersistenceChangedEvent” with the “mtPersistenceOffMode” parameter and the application signature of conferencing application  401 . Call director  502  will then remove the entry for conferencing application  401  from call director preference file  510  in block  824 , as described below. If conferencing application  401  is listening in the same way, then conferencing application  401  is transferred the incoming call as in block  806 . 
     In block  806 , and referring to FIG. 7, after the conferencing application has completed launching, or if the conferencing application is already executed, call director  502  will transfer the incoming call to the conferencing application, as described above, and return to listening, as discussed in block  822 , below. 
     After conferencing application  401  has been transferred the call, conferencing application  401  will then be responsible for giving the user an option to accept the call. If the user decides to accept the call, then conferencing application  401  will perform as usual an process the incoming call. If the user does not accept the call, then operation will continue with block  820 . It is to be noted that whether or not the user decides to accept the call, call director  502  is not affected after call director  502  has transferred the incoming call to conferencing application  401  and returns to listening, as discussed in block  822 . 
     In block  822 , after either: (1) call director  502  has transferred the incoming call to the conferencing application as in block  806 ; or (2) demon conference component  504  has dropped the call—i.e. removed the call from the incoming call event queue—as in block  826 , demon conference component  504  will return to listening. 
     In block  824 , where conferencing application  401  is not locatable or conferencing application  401  is not listening using the same values with which conferencing application  401  set-up call director  502 , call director  502  will remove all references to conferencing application  401  from call director preferences  510 . 
     In block  826 , if there is not enough memory available to launch conferencing application  401  and the user does not free-up any memory within the time-out period in block  816 , then the incoming call will not be answered and the caller will receive a notice that the user the caller is trying to contact is not available. The incoming call will also be dropped if conferencing application  401  is not listening in the same way as it was when conferencing application  401  set-up call director  502  to listen for incoming calls. If there is not enough memory available to launch conferencing application  401  and the user does not free-up any memory within the time-out period in block  816 , then the system will be the one shown in FIG. 5, where conferencing application  401  and conference component  400  are not executing. If conferencing application  401  is not listening in the same way as it was when conferencing application  401  set-up call director  502  to listen for incoming calls, then the system will be as shown in FIG. 6, where conferencing application  401  and conference component  400  are executing even though they are not processing any incoming calls. 
     Listening on Multiple Ports By Multiple Conferencing Applications 
     FIG. 9 illustrates a preferred embodiment of the invention for initiating persistent listening on multiple ports where the system of FIG. 6 (wherein conferencing application  401  and conference component  400  has set-up persistent listening, as discussed above) now includes a second conferencing application  518  and a second conference component  520 . Second conferencing application  518  and second conference component  520  is launched and initiated the same way as conferencing application  401  and conference component  400 . 
     It will be recalled that in the discussion of FIG. 6, transport component  506  and network component  508  have been initialized to listen for an incoming call matching the parameters of the listen string belonging to conferencing application  401 . Now, in FIG. 9, second conferencing application  518  wishes to set-up persistent listening under a different set of parameters (e.g. under AppleTalk, versus TCP/IP for conferencing application  401 ). The sequence followed by second conferencing application  518  is identical to the sequence performed by conferencing application  401 , except for the different value of the listen string passed to demon conference component  504  and call director  502  to set-up a different transport component and a different network component. 
     In FIG. 9, before second conferencing application  518  has requested and set-up persistent listening, there is only persistent listening being performed for conferencing application  401 . After second conferencing application  518  has set-up persistent listening, the system will be as shown in FIG.  10 . 
     In FIG. 10, after second conferencing application  518  has set-up persistent listening, a second transport component  514  instance and a second network component  516  instance has been created to perform the listening requested by second conferencing application  518 . Second transport component  514  and second network component  516  are identical to transport component  506  and network component  508 , except that they are set-up to listen for incoming calls having the parameters of the listen string of second conference component  520 . 
     In FIG. 11, an incoming call has come in matching the parameters of the listen string for conference component  400  and demon conference component has transferred the incoming call to conferencing  401 , as discussed above. 
     In FIG. 12, while conferencing application  401  is processing the incoming call received in FIG. 11, an incoming call has come in for second conferencing application  518  and has been transferred to second conferencing application  518  through the creation of a third transport component  522  and a third network component  524  to 
     Thus, the explanation give above in FIGS. 5-8 can be modified by substituting second conferencing application  518 , second conference component  520 , third transport component  522 , third network component  524 , second transport component  514  and second network component  516  for conferencing application  401 , conference component  400 , transport component  402 , network component  403 , transport component  506  and network component  508 , respectively, with the exception that there would now be a different listen string for second conference component  520 . In addition, listen strings list  412  and conferencing application alias list  414  in FIG. 4 would contain an additional listen string for second conference component  518  and an additional alias for second conferencing application  520 , respectively. For example, if second conferencing application  518  is not loaded when an incoming call matching the parameters of the listening requested by second conferencing application  518  came in, then second conferencing application  518  and second conference component  520  would be dynamically launched to handle the incoming call as discussed in FIG.  8 . 
     It is to be noted that not only can persistent listening for multiple ports can exist for multiple conferencing applications, multiple persistent listening can exist for a single conferencing application if there is more than one service in the listen string of the conference component of that conferencing application, as mentioned above. 
     While the present invention has been particularly described with reference to the various figures, it should be understood that the figures are for illustration only and should not be taken as limiting the scope of the invention. Many changes and modifications may be made to the invention, by one having ordinary skill in the art, without departing from the spirit and scope of the invention.