Patent Publication Number: US-8116301-B2

Title: Method and apparatus for multiple media digital communication system

Description:
The present application is a continuation of application Ser. No. 10/804,776 filed Mar. 19, 2004 of the same title, now U.S. Pat. No. 7,075,924, which is a continuation of application Ser. No. 09/596,835 filed Jun. 19, 2000 of the same title, now U.S. Pat. No. 6,738,357, which is a continuation of prior application Ser. No. 09/437,269 filed Nov. 10, 1999, now U.S. Pat. No. 6,104,706, which is a continuation of Ser. No. 08/795,798 filed Feb. 5, 1997, now U.S. Pat. No. 5,995,491, which is a continuation of Ser. No. 08/626,580 filed Apr. 2, 1996, now U.S. Pat. No. 5,623,490, which is a continuation of Ser. No. 08/073,956, filed Jun. 9, 1993, now abandoned. This application is related to co-owned application Serial No. 10/847,782 filed Jun. 22, 2004 entitled “Apparatus for Multiple Media Digital Communication”, now U.S. Pat. No. 7,050,425. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of digital communications systems, and more particularly to systems transporting multiple media (multimedia) and/or communicating such multimedia through a plurality of connections to multiple callers. 
     BACKGROUND OF THE INVENTION 
     In the prior art, multimedia communications, such as videoconferencing systems for providing two way video and audio, are well known. Given sufficient bandwidth and dedicated independent channels, (e.g. 6 Mhz for an analog video channel, 3 Khz for an audio link over a standard analog telephone line, etc), videoconferencing between two callers can be realized. However, communication channels providing 6 Mhz video bandwidth are not generally or universally available. A major obstacle to wide spread implementation and acceptance of multiple media conferencing systems is the limited bandwidth of the available communication channels. In addition, typical communication channels available on packet switched networks such as AppleTalk, from Apple Computer, California, USA, or Netware from Novell Inc, Oregon, USA, do not provide the continuous real time analog or digital connection of a telephone line or modem. Instead, packet switched networks provide non-real time bursts of data in the form of a switched packet containing a burst of digital data. Thus, in addition to bandwidth limitations, packet switched networks present delay limitations in implementing real time multiple media conferencing systems. The same bandwidth and time delay limitations which apply to all time division multiple access (TDMA) communication systems and similar schemes present obstacles to achieving real time multimedia communications. 
     Typically, the problem of videoconferencing two callers is approached by compressing the composite video signal so that the resulting transmitted data rate is compatible with the available communication channel, while permitting acceptable video and audio to be received at the other end of the communication channel. However, solutions in the past using lossy compression techniques, have been limited to compromising quality in order to obtain acceptable speed. Recently, non-lossy compression techniques have become available. The problem still remains as to how to match the bandwidth and timing constraints of available digital formats to the available communication channels, both present and future. 
     SUMMARY OF THE INVENTION 
     The present invention is embodied in a digital communication system where multiple media data sources are time multiplexed into a packetized data stream. At both the transmit side, and the receive side, audio packets are given priority processing over video packets, which in turn have priority over text/graphics data packets. Continuous real time audio playback is maintained at the receiver by delaying the playback of received audio in a first in/first out (FIFO) buffer providing a delay at least equal to the predicted average packet delay for the communication system. Optionally, the average system delay is continuously monitored, and the audio and video playback delay time as well as audio and video qualities are adjusted accordingly. In another embodiment of the invention, a conference of three or more callers is created by broadcasting a common packetized data stream to all conference callers. Use of the present invention further permits an all software implementation of a multimedia system. 
     1. In accordance with a first aspect of the present invention, multiple data sources forming data packets are combined into a prioritized data stream. 
     The present invention is embodied in a method and apparatus for combining data from a plurality of media sources into a composite data stream capable of supporting simultaneous transmission including multiple video and graphic signals and real time audio. Video, audio and other signals are integrated in a non-standard transmission format determined by a novel streaming algorithm and prioritization scheme designed to provide the best balance between transmission quality and realization of real time rendition of each. 
     For example, each data type packet at the transmitter is assigned a priority between 0 and 10000, with 0 being the highest priority and 10000 the lowest. An audio packet is given priority 20, a video packet is given priority 50. Screen data packets and file data transfer packets are both given priority 180. 
     Before transmission on the communication channel, packets are placed in a queue according to priority order. As new packets are generated, the queue is reorganized so that the new packet is placed into its proper priority order. 
     At the receiver, each task runs according to its assigned priority. Packets with priorities between 0 and 100 are processed first, to the exclusion of packets with priorities 101 through 10000. Audio, being the highest priority (20), is processed first to the exclusion of all other packets. Within the class of packets with priorities between 101 and 10000, packets are processed according to relative priority. That is, higher priority tasks do not completely shut out tasks of lower priority. The relationship among priorities is that a priority 200 task runs half as often as a priority 100 task. Conversely, a priority 100 task runs twice as often as priority 200 task. Tasks with priorities between 0 and 100 always run until completion. Thus, video, screen data and file data, processing tasks are completed after audio processing in accordance with the relative priority of the packets. 
     A multi-tasking executive dynamically reassigns task priorities, to efficiently complete all tasks within the available time, while performing the highest priority tasks first. At any given time, there are different tasks all at different priorities, all yielding to each other. In general, a task yields to a higher priority task, if it is not running an uninterruptable sequence. If the current task completes its cycle, its priority is reassigned to a lower priority. If the priority of two or more tasks is equal, then the multi-tasking executive executes each task in a round robin fashion, performing a portion of each task, until the completion of all tasks with the same priority. 
     The assignment of packet priorities, and processing according to priority assures that audio will be given precedent over video, while audio and video will be given precedent over both screen data and file transfer data. 
     As indicated above, continuous real time audio playback is maintained at the receiver by delaying the playback of received audio in a first in/first out (FIFO) buffer having a size at least equal to the predicted average packet delay for the communication system. Optionally, the delay of the audio FIFO may be made variable. A variable delay audio FIFO buffer at the receiver allows the system to shrink or grow the time delay between one machine and the other. The ability to shrink or grow the difference in time between the sender and receiver permits the system of the present invention to compensate for indeterminate system delays. If the changes are slight, the difference in pitch is not noticeable. For greater changes, the technique of audio resampling may be used to increase or decrease the rate of audio playback without changing the pitch of audio content. 
     Similarly, video playback continuity at the receiver may also be improved by delaying the playback of received video in a first in/first out (FIFO) buffer having a size at least equal to the predicted average packet delay for the communication system. The delay of the video FIFO may be made variable, allowing the system to shrink or grow the time delay between one machine and the other to compensate for indeterminate system delays. Again, if the changes are slight, the change in frame rate is not noticeable. However, video data does not age as quickly as audio data. Therefore a smaller video FIFO can be used. Also, a video image may have short discontinuities without a perceived loss of the video connection. Audio playback, on the other hand, is more sensitive to discontinuities, and it is more important to maintain continuity at the receiver. Ideally, when both audio and video are used in a multimedia conference, the delay for audio and video should be equal to make sure that they are synchronized. In the latter case, the actual system delay is calculated by finding the maximum delay of both audio and video packets. 
     Data from media sources tend to come in bursts. For example, audio data rates rise when speaking, and fall to zero during a silence. In the present embodiment, the silence between words provides the present system with an opportunity to catch up by refilling the audio FIFO buffer before it empties. In such manner, the present system compensates for the delay inherent in a packet switched, time delay variant, communication channel. 
     Similarly, video sources including graphic screen data, are generated in bursts. That is, the data rate for video ideally falls to zero when there is no motion. The data rate for transmitting screen graphics falls to zero when are no changes. When the caller changes the screen, (such as the collaborative work document displayed on the screen), data is generated. 
     Thus, following the priority scheme of the present invention, video is updated only when no speech data is being processed. However, processing of speech data does not included the playing of sound. Once the sound starts playing, there is no need to further spend time to process the sound. Sound playing needs no supervision. Therefore, video updating occurs while sound is playing. After speech is playing close to real time (with a delay), video text and graphics are updated in the background. Video, text, graphics and data files are updated at lesser priorities. Except for audio and video data, task priorities are re-assigned to assure that all tasks will be completed, and that a higher priority task will not completely prevent the lower priority tasks from being completed. 
     2. In accordance with a second aspect of the present invention, multiple signal packets are broadcast to a plurality of callers to create a common multimedia conference. 
     In addition to assigned priorities, data packets having multiple destination addresses are broadcast over a plurality of connections to multiple callers. Each caller receives the same data packets with assigned priorities, and processes the received packets in a similar manner. As new data is generated from each caller in the video conference, new data packets are broadcast to the other callers. Thus, due to the broadcast of data packets representing audio, video and screen data, all callers are conferenced together, each seeing and hearing each other, while discussing the same screen document. Additional callers can be added to the conference over a plurality of connections without adding undue burden, because in a conference, each caller needs to generate data only once, which is then transimtted either simultaneously or sequentially depending on the kind of connection, to other callers. 
     3. In accordance with a third aspect of the present invention data received on a first communication medium (for example on a broadband local area network, such as ethernet) are re-broadcast on a different communication medium (such as a telephone line) in order to conference callers on the different communication media in a common multimedia conference. The present invention thereby provides the option of desktop videoconferencing on standard computer networks and telephone lines. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a dialog box indicating connection status as it would appear on the screen of a Macintosh computer used in conjunction with the present invention. 
         FIG. 1B  is a dialog box indicating an incoming call as it would appear on the screen of a Macintosh computer used in conjunction with the present invention. 
         FIG. 1C  is a dialog box illustrating the connection status message that would appear for a call that was not accepted as it would appear on the screen of a Macintosh computer used in conjunction with the present invention. 
         FIG. 1D  is a window containing a moving video image as it would appear on the screen of a Macintosh computer used in conjunction with the present invention. 
         FIG. 2  is a video screen illustrating a video conference between two callers and sharing a common document. 
         FIG. 3  is a video screen illustrating a video conference between three callers and sharing a common document. 
         FIG. 4  is a block diagram illustrating the sequence of operations for establishing a connection in a multiple media digital communication system embodying the present invention. 
         FIG. 5  is a block diagram illustrating the sequence of operations for establishing media types to be used in a conference call in a multiple media digital communication system embodying the present invention. 
         FIG. 6  is an illustration of a packet data format used in conjunction with the present invention. 
         FIG. 7A  is a block diagram of a multiple media communication system transmitter in accordance with the present invention. 
         FIG. 7B  is a block diagram of a multiple media communication system receiver in accordance with the present invention. 
         FIG. 8  is a block diagram of a method and apparatus for processing a data packet in accordance with the present invention. 
         FIG. 9  is a block diagram illustrating the sequence of operation of a method and apparatus for processing data packets in accordance with the present invention. 
         FIG. 10  is a block diagram of a method and apparatus for establishing a connection for specific media between callers used in conjunction with the present invention. 
         FIG. 11  is a block diagram illustrating the sequence of data packet flows with optional acknowledgement handshake packets. 
         FIG. 12  is a block diagram of a multiple media digital communications system for sending and receiving multiple media for a first caller in accordance with the present invention. 
         FIG. 13  is a block diagram of a multiple media digital communications system for receiving and sending multiple media for a second caller in accordance with the present invention. 
         FIG. 14  is a first configuration of the present invention for conducting a standard videoconference call over an ethernet network. 
         FIG. 15  is an alternate configuration of the present invention for conducting a standard videoconference call with collaborative data over an ethernet network. 
         FIG. 16  is an alternate configuration of the present invention for leaving a recorded multimedia message of a videoconference call with collaborative data over an ethernet network. 
         FIG. 17  is a three caller multimedia conference call in a system in accordance with the present invention. 
         FIG. 18  is an alternate embodiment of a three caller multimedia conference call in a system using both ethernet and a telephone modem in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     From the viewpoint of the caller, the present multimedia communication system operates as follows: 
     A caller on a desktop computer initiates a multimedia call by selecting a media type and desired connection with a second party. A dialog box of the type shown in  FIG. 1A  appears on the screen, illustrating the connection status. Caller  2 , who receives the call, views a dialog box on his screen of the type illustrated in  FIG. 1B  to announce an arriving call. Caller  2  has the option of deciding to either pick up or deny the call, or to take a message. If the call is denied by caller  2 , then caller  1  views a dialog box  14  as illustrated in  FIG. 1C . For purposes of illustration, a video box  16  containing a video of the first caller  1  is shown in  FIG. 1D . If the caller decides to take a message, caller  2  can now control the connection and optionally send an announcement message requesting a message. 
       FIG. 2  illustrates the screen appearance of a typical multimedia call with a collaborative document. On the screen  20  of caller  1 , a video box  24  appears in which a moving video showing caller  2  appears. The screen of caller  2  is similar, but contains the image and sound of caller  1 . On both the screens of callers  1  and  2  can be a collaborative document  22 . Caller  1  and caller  2  are connected by moving video and two way audio and can discuss collaborative document. Caller  1  may manipulate the document and the changes will appear on the screen of caller  2 . In an alternate embodiment, caller  2  may manipulate the document as well. 
       FIG. 3  illustrates the screen  20  appearance of a three party video conference as it appears to caller  1 . Caller  3  appears in a video box  26  as well as caller  2  in another video box  26 , and the collaborative document  22 . The other callers  2  and  3  see the other two members of their video conference on their screen as well as collaborative document  22 . The size and position of video boxes  24  and  26  is selectable by caller  1 . A video image  25  of caller  1  may also appear on the screen of caller  1  to let caller  1  see what is being transmitted. Reducing the size of video box  25  reduces the amount of (video) data which must be transmitted by the communication system. 
     Connection Establishment 
     The sequence of operation for establishing a connection between caller  1  and caller  2  over a communication network is illustrated in  FIG. 4 . The network may typically be AppleTalk, ethernet or any other commonly available local area network. Also, a connection can be established over a telephone line or other proprietay digital telephone lines such as ISDN. 
     The terms, “connection stream” and “media stream” used below are further defined in the description of  FIGS. 8-11 . For present purposes, such terms may be regarded as routines for handling data packets. Caller  1  selects a media type stream  28 , and a connection stream  30 , suitable for the communication medium. An initial message termed a helo packet is sent to a caller  2  connection stream  32 . The connection stream  32  provides a dialog box to caller  2  informing that there is an incoming call from caller  1 . Caller  2  can then decide  34  to either accept or deny the call, or alternatively to take a message if caller  2  is not present. The accept, deny and take commands are communicated back to the connection stream  32  which sends a return message across the communication system back to connection stream  30  and caller  1 . 
     In addition to denying or taking the call, caller  2  has the option to pick a different media type. That is, for example, if the media type stream  28  of caller  1  is video, and caller  2  does not want to accept a video call but will accept an audio call, then the return message pick will indicate that caller  2  is picking audio as the media for an incoming call. At caller  1 , connection stream  30  distributes the response from caller  2 . Specifically, if the call is denied then the connection attempt is deleted  40 . If a different media is picked, then a modification of the media type stream  28  is performed. If take a message was selected, then the appropriate file transfer  38  takes place to transmit an announcement file, and a message is requested to be sent back. 
       FIG. 5  illustrates the communication sequence for selecting the among the various media types between caller  1  and caller  2 . For media type stream  42 , a request is sent through connection stream  44  across the communication channel to caller  2  at connection stream  46  which is forwarded to media type stream  48 . Caller  2  configures itself to accept the media type stream which is being presented to it by modification of its registration server  50  which clones the desired media type. If accepted, media type stream  48  sends a message through connection stream  46  across the communication medium to caller  1 . The acceptance is received at connection stream  44  and communicated to media type stream  42  which opens up the connection for the given media type between caller  1  and caller  2 . 
     Data Format in Packets with Priority and Multiple Destinations 
       FIG. 6  shows a packet data format  52  suitable for use in conjunction with the present invention. The length of the packet is indicated by data field  54 . The length of the header is indicated by data field  56 . The packet type and identification are respectively indicated by data fields  58  and  60 . 
     The priority of the data packet is indicated in data field  62 . When transporting multiple media digital data packets, the priority data field determines which of the packets has the highest priority in processing. Data fields  64  and  66  respectively contain information as to the message state, and a checksum for determining message errors. The packet source address is indicated at data field  68 , and a destination count as to the number of destinations this packet will reach is indicated at data field  70 . Also, an active destination count, the number of destination which have not yet received this packet, and a maximum destination count is provided in data fields  72  and  74  respectively. 
     The data packet  52  of  FIG. 6  contains a number of destination addresses  76 . The plural destination addresses provides a broadcast capability by which all the callers in a conference call can view common documents and see and hear each other. That is, when a data packet  52  contains audio data representing one speaker&#39;s voice, that packet is broadcast to all the destinations simultaneously. The same is true of the video and document updates. The destination addresses is followed by the actual variable length data of the data packet in field  78 . 
     System Overviews 
     A block diagram of a multiple media communication system transmitter is shown in  FIG. 7A . A packet with priority 20 is generated  708  from audio data source  702 . A packet with priority  50  is generated  710  from video data source  704 . A packet with priority 180 is generated  712  from text/graphics data source  706 . A WriteQueue  716  (a buffer memory for storing packets to be sent) is provided for holding packets to be transmitted over the communication channel  718 . Control  714 , responsive to packet generation,  708 ,  710 ,  712  places the packets in the WriteQueue  716  in order of packet priority. In hardware, a queue maybe a FIFO. In software, WriteQueue  716  is a linked list of packet containers with pointers to the next and previous packet containers. Since the Writequeue  716  is an ordered list, adding a new entry is achieved by modifying two pointers to add the new entry to the list in the proper order. 
     A block diagram of a multiple media communication system receiver is shown in  FIG. 7B . Two substantially similar receivers, one for caller  2  and another for caller  3  are illustrated. Both callers are respectively connected to a broadcast communication channel  720 ,  746 . A ReadQueue  722 ,  724  (a buffer memory for storing packets) receives packets for processing. A control means  726 ,  728  selects packets to be processed based on the packet priority. A multi-tasking control  730 ,  738  processes data-packets in accordance with assigned priorities. As indicated, audio packets have the highest priority and are processed first. Other packets are processed in accordance with priority in a multi-tasking environment which balances speed of execution among the different priority packets while making sure to complete all tasks. A variety of multi-tasking control techniques for completing multiple tasks simultaneously, giving priority to higher tasks, while devoting some system resources to complete the lowest priority tasks, are known to those skilled in the art. 
     Audio data playback is delayed in a delay  734 ,  742 , as indicated above. Video data display is similarly delayed in delay  731 ,  739  to maintain synchronism between video and audio. The multi-task control  730 ,  738  sets the amount of delay (for both video and audio) in accordance with the predicted average delay of the communication channel  720 ,  746 . Delayed audio is then displayed  736 ,  744  at the receiver for caller  2  and caller  3 . Delayed video is simultaneous displayed  732 ,  740  at the receiver for caller  2  and caller  3 . Furthermore, since callers  2  and  3  are both receiving the same packets broadcast by caller  1 , both hear and view the same multimedia messages. 
     Multimedia communication is typically two way between all callers. It should be understood that caller  1 , caller  2  and caller  3  all include the transmitter and receiver elements shown in  FIGS. 7A and 7B . This does not mean, however, that all callers need to transmit or receive data. Each caller can choose to (or be required to) receive only or transmit only. 
     In operation, at caller  1  in  FIG. 7A , successive multimedia data packets with assigned priority are generated  708 ,  710 ,  712  from respective multimedia sources  702 ,  704  and  706 . As the packets are generated, each is placed  714  in priority order in a queue  716  and transmitted over a communication channel  718 . If the channel capacity were unlimited, packets would be transmitted as soon as generated. However, in the normal case, generated packets may accumulate awaiting transmission because the communication channel capacity is limited. The present priority scheme assures that packets are transmitted in priority order with the highest priority packets transmitted first. 
     At the receiver, callers  2  and  3  in  FIG. 7B  both receive packets from the communication channel  720 ,  746 . Received packets at callers  1  and  2 , are processed in accordance with the received priority, to play back the received audio, video and display of the received text/graphics. Since both callers  2  and  3  receive the same packets, a three party videoconference call is created. 
     Continuity of audio playback is perceived as critical to a multimedia conference. Accordingly, audio packets, being assigned the highest priority, are sent as soon as possible, and at the receiver, are processed as soon as possible after receipt. Thus, audio packets tend to be delivered in the shortest time which the communication channel will allow. 
     The system of the present invention tolerates transmission errors inherent in a traditional packet switched system by discarding or retransmitting corrupted audio or video. For text files, the normal error detection and retransmission requests are used. Sound and video are distinguished from text or file data in that it is possible to tolerate some loss of sound and video and still maintain an acceptable quality. In the event of a detected error in the received audio or video packet, the receiver determines whether there is sufficient time to flag the error and request a retransmission, based on the predicted average delay time of the system. If there is not sufficient time, the corrupted packet is ignored. In such manner, network capacity is not wasted on retransmissions which will arrive too late and have to be discarded anyway. However, the lowest priority packets of text/graphics or computer file data which are not time dependent, are flagged for errors and retransmitted. 
     Object Oriented CPacketStream Streaming Method 
     Various types of streams are used to achieve multimedia communications. First, a connection stream provides the interface to the communication channel. Then, there is a media stream for each desired media. For example, there may be a video stream, an audio stream, a video and audio stream such as QuickTime, or a text/data/graphics stream representing files, graphic images of many types, or any other data required. The architecture is designed to support “drop in” streams for new kinds of collaborative data. 
     The block diagram of  FIG. 8  illustrates the method and apparatus for sending and receiving data packets, also termed CPackets. Each of the above methods and tasks is described in detail below, including pseudo code for realizing each of the methods and tasks on a general purpose digital computer. Although the preferred embodiment is described in terms of software operating in a Macintosh computer environment, it will be understood that the present multiple media communication system of the present invention may be implemented in hardware, such as in dedicated logic, microprogrammed bit slices, programmable arrays and the like. 
     CPacketStream  80  is a software component which is responsible for handling CPackets to establish communication channels between machines. Each CPacketStream  80  is composed of a set of routines (or methods) responsible to interact with CPackets. These methods are used in turn by a set of tasks running in each CPacketStream. The task types and methods (or routines) available for packet handling are summarized as follows and described in more detail below. 
     
       
         
           
               
             
               
                   
               
               
                 TASKS: 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 WriteTask 
                 (prioritized multi-tasking of received CPackets) 
               
               
                   
                 ReadTask 
                 (connection stream distributes received CPackets) 
               
               
                   
                 IdleTask 
                 (send final packet and initial packet) 
               
               
                   
                 OpenTask 
                 (open connection stream) 
               
               
                   
                   
               
            
           
         
       
     
                             METHODS                                                DoQueue   (puts a Cpacket in the WriteQueue)           DoWrite   (generates actual output from packet data)           DoIdle   (idle between packets)           Write   (lookups destination and calls DoQueue)           WriteDone   (acknowledges receipt of packet)           WriteQueue   (A buffer containing CPackets in priority order)           ReadQueue   (A buffer containing CPackets in received order)                        
CPacketStream::WriteTask  94 
 
     The WriteTask  94  is responsible for distributing packets contained in the WriteQueue  96  in each CPacketStream  80 . The priority of this task is at least as high as the packet it is currently handling. This task is in a loop currently scanning the WriteQueue  96 , if the queue is empty then the task will sleep. The CPacketStream::DoQueue method will put a CPacket into the WriteQueue  96 , and wake the WriteTask  94  up. Therefore, the WriteTask  94  will be the one displaying or playing the packets. 
                                            CPacketStream::WriteTask                         if a packet in WriteQueue                         call DoWrite for that packet to handle data                         end                         end                        
CPacketStream::ReadTask  82 
 
     The ReadTask  84  is responsible for reading CPackets from a particular channel, and redistributing among CPacketStreams  80  in that machine. This type of task is only appropriate for a connection (media) CPacketStream  80 . (In a way it is similar to the WriteTask  94 , serving a WriteQueue  96 , but in the reverse direction, and corresponding to receiving data packets in a ReadQueue) 
                                            CPacketStream::ReadTask                         if a new packet read                         write a new packet                         end                         end                        
CPacketStream::IdleTask  82 
 
     The idle task  82  is responsible for generating and sending ‘helo’ (the initial packet) and ‘kiss’ (the final packet) CPackets. It is also responsible to execute idle time events in some particular streams. For example, a Communications Tool (from Apple Computer) needs to have an idle call every so often in order to handle a particular connection. 
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 CPacketStream::IdleTask 
               
            
           
           
               
               
            
               
                   
                 if initial packet not sent 
               
            
           
           
               
               
            
               
                   
                 if initial packet not created 
               
            
           
           
               
               
            
               
                   
                 create initial packet 
               
            
           
           
               
               
            
               
                   
                 end 
               
               
                   
                 sent initial packet 
               
            
           
           
               
               
            
               
                   
                 end 
               
               
                   
                 idle stream if necessary 
               
               
                   
                 if stream should die 
               
            
           
           
               
               
            
               
                   
                 if final packet not created 
               
               
                   
                 create final packet 
               
            
           
           
               
               
            
               
                   
                 end 
               
               
                   
                 send final packet 
               
            
           
           
               
               
            
               
                   
                 end 
               
               
                   
                 if final packet sent and stream should die 
               
            
           
           
               
               
            
               
                   
                 disable and delete the streams 
               
            
           
           
               
               
            
               
                   
                 end 
               
            
           
           
               
               
            
               
                   
                 end 
               
               
                   
                   
               
            
           
         
       
     
     An OpenTask  88  is used when the connection is being first opened and the connection negotiated between callers. At that time, the contents of the table lookup  98 , which defines media types and connection streams is determined. In addition to these tasks, there are several methods that are called by these tasks in order to communicate with the stream. These methods are: 
     CPacketStream::DoQueue  86   
     This is the method that is called in order to give a packet to a particular stream. Most streams will immediately write the packet to a WriteQueue  96 , and activate the WriteTask  94  in order to handle that particular packet. 
                                            CPacketStream::DoQueue 86                         put packet into the write queue           wakeup WriteTask                         end                        
CPacketStream::DoWrite  92 
 
     The WriteTask  94  will call this routine to actually handle the packet&#39;s content. For a connection stream, this is the output routine of a CPacketStream  80  to the communication channel. For a video stream, this routine will decompress and display the video contained in a packet. For other media streams, the DoWrite  92  routine will carry out the appropriate process to get the data displayed, played or otherwise. 
                                            CPacketStream::DoWrite                         handle the packet&#39;s data                         end                        
CPacketStream::DoIdle
 
     This is the routine which can be used to idle the CPacketStream  80 . Many streams can use this to do periodic tasks. 
                                            CPacketStream::DoIdle                         perform periodic task                         end                        
CPacketStream::Write  90 
 
     This routine will look up in table  98  the destination address for each destination in the packet, and the call DoQueue  86  for each destination packet stream. Each DoQueue  86  can refuse the packet until a later time, and therefore the packet contains flags for each destination address such that a complete write will mark that address completely written. A packet therefore contains an active destination count ( 72  in  FIG. 6 ). 
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 CPacketStream::Write 
               
            
           
           
               
               
            
               
                   
                 for all destination addresses in packet 
               
            
           
           
               
               
            
               
                   
                 lookup destination stream in address table 
               
               
                   
                 if alias entry and ‘info’ packet 
               
            
           
           
               
               
            
               
                   
                 add writeAsRemoteInfo flag 
               
            
           
           
               
               
            
               
                   
                 end 
               
               
                   
                 if found 
               
            
           
           
               
               
            
               
                   
                 call DoQueue method for destination stream 
               
               
                   
                 if successful 
               
            
           
           
               
               
            
               
                   
                 mark destination address write complete 
               
            
           
           
               
               
            
               
                   
                 end 
               
            
           
           
               
               
            
               
                   
                 else 
               
            
           
           
               
               
            
               
                   
                 mark destination address write deleted 
               
            
           
           
               
               
            
               
                   
                 end 
               
            
           
           
               
               
            
               
                   
                 end 
               
            
           
           
               
               
            
               
                   
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     Data packet flow and handling through CPacketStream  80  is from calls to DoQueue  86  which will write a CPacket into the WriteQueue  96 , and then activate WriteTask  94 , which processes the Cpackets, and calls DoWrite  92  to distribute the Cpackets contained in the WriteQueue  96 . 
     CPacketStream::WriteDone 
     This routine will be called to dispose of the packet generated by a certain stream. It can be used for synchronization. A connection stream has the option of calling WriteDone to transfer acknowledge packets on the outgoing connection. The CPacketStream owns the packet which it sends, until all other streams are done with the packet. At that time, the packet ready to be deleted. However, when a packet (e.g., video) is sent from one machine on to another machine, such as between an ethernet LAN (local area network) and a telephone modem, the packet (e.g., the video) is not actually being used. In such circumstances, the originating connection stream should hold the packet, until all other connections have used this packet on the other machine(s). Synchronization of packet receipt is accomplished by returning an acknowledge packet when the WriteDone function of the connection stream is called at each machine which receives the packet. This is an additional form of communications between machines to reinforce the normal packet communications. “Acknowledge” packets have the same priority as the information packets, the lowest packet priority. 
     Streaming Algorithm 
     A generalized representation of the use of the present streaming algorithm is shown in the block diagram of  FIG. 9 . Two CPacketStreams, CPacketStream A,  801  and CPacketStream B,  802  are shown. By way of example, if CPacketStream A was a connection stream, then CPacketStream B would be a media stream, such as a video stream. On the other hand if CPacketStream A was a video stream, such as from a frame grabber, then CPacketStream B would be a connection stream. In general, there is one stream for each type of media, plus one stream for each connection. That is, a separate connection stream is used for each caller. Thus, for a two way conference with one other caller, there is one connection stream, while for a three way conference there are two connection streams, one for each of the other two callers. In an alternate embodiment, such as may be used with future higher speed communication systems, a single connection stream may be used with more than one caller. 
       FIG. 9  also shows a lookup table  818  which is filled in when each stream is established for keeping track of the destination of the various packets. In operation, a packet is generated  804  and the Write function  806  is called. The pseudo code  816  for the Write function  806  contains a reference to a lookup to table  818 , which returns an address to CPacketStream B,  802 . CPacketStream B,  802  calls DoQueue  812 , which writes the CPacket to WriteQueue  810 . WriteTask  814  is activated to process the CPacket, which calls DoWrite  808  to generate the output routine of a CPacketStream  80  to the communication channel, or other appropriate media output. 
       FIG. 10  illustrates the use of lookup tables to generate destination addresses from connection information between two given callers. By way of example, assume that CPacketStream A,  904  is a video stream connected to frame grabber  902  and image decompressor  912  at machine  1 . A machine  2 , CPacketStream D,  910  is also a video stream connected to a frame grabber  920  and image decompressor  918  at machine  2 . Then, CPacketStream B,  906  is a connection stream coupled to a communication channel interface  914 , such as for example a transmission source for an AppleTalk Data Streaming Protocol (ADSP) device. CPacketStream C,  908  is a connection stream coupled to a communication channel interface  916 , shown as the receiving side of an AppleTalk Data Streaming Protocol device. Machine  1  uses table  922  to lookup the destination stream address  2 ,D for packets generated using data from video grabber  902 . Similarly, machine  2  uses lookup table  925  to lookup the destination stream address  1 ,A for packets generated using data from video grabber  920 . 
     Packet Acknowledgement 
     A block diagram illustrating the use of an optional acknowledgement packet is shown in  FIG. 11 . A media stream  928 , responsive to a video packet  936 , calls the Write function, which through the appropriate lookup table, calls the DoQueue and DoWrite functions of connection stream  930 , an ethernet connection stream. The video packet is transmitted on the ethernet communication channel  938  and received by the ReadTask and Write functions of connection stream  932 . Thereafter, the DoQueue and DoWrite functions of media stream  934  are called through the appropriate lookup table which displays the data on video display  940 . 
     The communication channel LAN protocol typically supports lower level acknowledgment functions. For example, it is known by the transmitting caller that the packet was received over the clear communication channel  938 . Otherwise, the LAN protocol (at the ADSP level for example) would have returned an error indication. In addition to the acknowledge at the LAN protocol level, an acknowledge packet is generated when the received data is played (i.e., when the video data is displayed) in order to provide end to end synchronization information. The WriteDone function of connection stream  932  generates such acknowledge packet for return transmission across communication channel  938 . Back at the originating transmitting caller, the ReadTask function of connection stream  930 , calls WriteDone routine of media stream  928  to process the acknowledge packet. The receipt of an acknowledge packet also provides an indication of system delay for the media type of media stream  928 , in this example, a video packet. The acknowledge packet contains a recorded time indicating when the video packet was actually used. Comparison of the recorded transmission time with the received recorded display time, provides a measure of the end to end system delay. 
     Prioritized Data Packet Processing 
     A system block diagram is illustrated in  FIGS. 12 and 13 .  FIG. 12  shows the transmission elements in solid lines and the receive elements in dotted lines.  FIG. 13  shows the receive elements in solid lines and the transmit elements in doted lines. 
     In  FIG. 12 , and audio data source  110  and video data source  112  are coupled through audio/video stream  114  and connection stream  116  to data communication channel  118 . In  FIG. 13 , data communication channel  118  is coupled to connection stream  216 , and then to audio/video stream  214 . Audio is played by sound manager  220 , which includes a FIFO delay buffer  228 . Video is played back by video decompressor  224  coupled to video display device  226 . 
     For the return direction,  FIG. 13  also shows audio data source  210  and video data source  212 , coupled to the communication channel  218  through audio/video stream  214  and connection stream  216 . At the transmission side in  FIG. 12 , audio is played by sound manager  120 , which includes a FIFO delay buffer  128 . Video is played back by video decompressor  124  coupled to video display device  126 . 
     In operation in  FIG. 12 , data generated by audio source  110  and video data source  112  are placed into packets in audio/video stream  114 , and forwarded to connection stream  116 . The connection stream arranges the available packets in priority order before transmission on the network communication channel  118 . Once transmission of a packet has begun, however, it is typically not interruptable. For example, if a video packet represents a video frame update, and the video packet transmission has started, no audio packet can be sent until the current packet is completed. If it is desired to improve audio transfer, the video frame update may be divided into smaller sub-frame packets. Then, an audio packet will be inserted during transmission of a complete video frame update, i.e., by insertion between sub-frame packets forming the video frame update. 
     In  FIG. 13 , data packets received by connection stream  216  are distributed to the audio/video stream  214 . Audio data packets, having a higher priority represent a higher priority task. Thus, the sound manager  222  is given priority over the video decompressor  224 . As indicated above, delay buffer  228  is set equal to the predicted average packet transmission delay of the communication system. Alternatively, the delay provided by delay buffer  228  is dynamically adjustable according to system delay as measured by time reported by return message packets or acknowledge packets. Audio playback is slowed or accelerated in order to shrink or grow the difference in time between the sender and receiver. 
     Additional media types, such as file text or screen documents may be added to the block diagrams of  FIGS. 12 and 13  as additional inputs to the Write function of stream  114  in  FIG. 12  and additional outputs of stream  214  in  FIG. 13 . In sharing collaborative documents, one member of the conference may be running the application such as a word processor or spreadsheet, and the others viewing a screen only. Alternatively, one member of the conference may be running the application, but the keystrokes of the others are transmitted back to the one member as text data. In such manner, conference members may each have direct input into the collaborative application. 
     As indicated, the preferred embodiment of the present invention is in software running on a Macintosh computer. A software embodiment has the advantage of being hardware independent, capable of working with any available media source, and across any available communication system. In addition, CPacketStream tasks and methods are shared by various connection streams and media streams. It is noteworthy that the present system achieves multimedia conferencing in a uniprocessor architecture. 
     Alternative embodiments of the present multimedia communication system include multi-processor architectures where the multi-tasking of received multimedia data packets may be replaced by parallel processing, or in special purpose hardware. In dedicated hardware, each CPacketStream could be a special purpose microprogrammed integrated circuit, where one chip would be required for each media type, and for each connection. 
       FIGS. 14 through 18  illustrate the various capabilities of the present system of multiple media digital communication.  FIG. 14  illustrates a standard video call of the type shown in  FIG. 2  over an ethernet network of the type illustrated.  FIG. 15  illustrates a video call with collaborative data over an ethernet network of the type illustrated on the screen in  FIG. 3 . This configuration is contemplated as the most common type of multimedia call. 
       FIG. 16  illustrates a one way video/audio call with collaborative data over an ethernet network. The data is one way because first party did not answer, but that party was configured to accept messages. The received data is recorded in memory or on disk and played back later, thus creating a multimedia message answering machine. In the message record mode, system delays are not limiting because the message does not have to be recorded in real time; the only requirement is to play it back in real time. The message is recorded on one machine, and sent as a complete message file to the other machine, and there stored on the drive. 
     A three way videoconference call is illustrated in  FIG. 17 . Caller  1 , caller  2  and caller  3  are connected over an ethernet communication system. Each caller broadcasts multimedia digital packets to the other two callers. The connection may be expanded to more than three callers. Each caller will see a video image of all the other conferences on their screen in separate windows, as well as hear the conversation and view collaborative data. 
     An alternate embodiment for a three way videoconference call is illustrated in  FIG. 19 . Two callers ( 1  and  3 ) are on ethernet. Another caller,  2  is connected by modem. Caller  3  links caller  1  to caller  2 . To link callers  1  and  2 , caller  3  rebroadcasts received data packets from caller  1  over ethernet, to caller  3  over modem, and vice versa.