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United States Patent4710917
Tompkins , ; et al.December 1, 1987
Title
Video conferencing network
Abstract
A video conferencing network includes remote video terminals (10) interconnected to a switching network (66) through coaxial cables (16). The switching network (66) is operable to provide an audio and video data path between two or more video terminals (10). The switching network (66) operates as both an audio/video crosspoint switch and also as a network controller. In the network control mode, the switching network (66) operates in both a master mode for maintaining data communication with all of the video terminals (10) and also in a slave mode for maintaining status of devices attached to the switching network (66). In the master mode, the switching network (66) receives requests from each of the video terminals (10) and services these requests to determine available data paths for interconnection with other video terminals. In the slave mode, the switch (66) is in data communication with all of the video terminals (10) to determine the status thereof which is stored in a slave status table. This information in the status table is transferred to a separate network table that is maintained in the master mode for network purposes.
Inventors:Tompkins; E. Neal (San Antonio, TX), Arends; Thomas C.  (San Antonio, TX), Barry; Michael W.  (San Antonio, TX)
Assignee:Datapoint Corporation (San Antonio, TX)
Appl. No.:721281
Filed:April 8, 1985
Current U.S. Class:709/204 709/208 710/316 348/14.08 348/14.11 370/260 370/271 379/202.01 
Field of Search:370/62,110.1,58,71,73,124,76 179/18BC,2TV,2TS 358/85 379/202,204,206
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Primary Examiner: Olms; Douglas W.
Assistant Examiner: Chin; Wellington
Attorney, Agent or Firm:Mills; Jerry W. Howison; Gregory M.
Claims

What is claimed is:
1. A video conferencing network, comprising:
a plurality of video terminals each having a unique address for transmitting and receiving audio, video and data;
switching means for receiving audio and video information at one of a plurality of audio/video ports and selectively transmitting said received audio and video information to one or more of the remaining of said audio/video ports;
data manager means for receiving data at one of a plurality of data ports, determining which of the remaining of said data ports the received data is to be transmitted to in accordance with predetermined routing information and transmitting the received data to the determined one of said data ports;
communication link means disposed between each of said video terminals and a select one of said audio/video ports on said switching means and a select on of said data ports on said data manager means;
slave means for controlling the configuration of said switching means in response to receiving a reconfiguration signal from said data manager means, said slave means in data communication with a select one of said data ports on said data manager means;
network master means for cotnrolling the network, said network master means receiving data from said data manager means and transmitting data thereto, said network master means communicating with said video terminals and said slave means, said network master means generating said reconfiguration signal for transmission to said slave means through said data manager means to reconfigure said switching means; and
data link means for interfacing between said network master means and one of said data ports on said data manager means.

2. The network of claim 1 wherein said switching means comprises:
audio multiplexer means for receiving audio from all of said audio/video ports and summing audio from select ones of said ports in accordance with said reconfiguration signal for transmission to one or more of the remaining of said audio/video ports; and
video multiplexing means for receiving video from each of said audio/video ports and selectively connecting the received video from one of said ports to one or more of said audio/video ports such that only one of the received video signals is transmitted to any one of said video terminals.

3. The network of claim 1 wherein said communication link means comprises:
a transmission medium associated with one of said video terminals, one of said audio/video ports on said switching means and one of said data ports on said data manager means;
first encoding means associated with each of said video terminals for receiving audio, video and data from the associated one of said video terminals and encoding it in a predetermined manner for transmission along a first path in said transmission medium, said first encoder means receiving encoded audio, video and data from a second path in said transmission medium and outputting decoder audio, video and data to the associated one of said video terminals; and
second encoding means for receiving encoded audio, video and data from said first path in said transmission medium and outputting decoded audio and video to said switching means and decoded data to said data manager means, said second encoding means receiving audio and video from said switching means and data from said data manager means and encoding said received audio, video and data in said predetermined manner and transmitting it on said second path in said transmission medium.

4. The network of claim 3 wherein said transmission medium includes a third bidirectional path for carrying information not associated with the network, information carried on said third path isolated from information carried on said first and second paths that is associated with the network.

5. The network of claim 3 wherein said transmission medium comprises a coaxial cable and said predetermined encoding pattern comprises frequency division multiplexing.

6. The network of claim 5 wherein said first and second encoding means comprise:
means for demodulating the encoded transmission to separate the transmitted audio, video and data information; and
means for receiving audio, video and data information and modulating a carrier frequency for transmission through said coax.

7. A video conferencing network, comprising:
a plurality of remotely disposed video terminals for transitting and receiving audio, video and data and each attached to one of a plurality of network ports, each of said network ports for receiving and transmitting audio, video and data;
switch means for receiving audio and video from each of said network ports and interconnecting the received audio and video for transmission to select ones of said network ports in accordance with a predetermined interconnect pattern;
data manager means for receiving data from each of said network ports, identifying the destination of the received data, and routing the received data to the one of said network ports corresponding to the identified destination;
slave means attached to one of said network ports for reconfiguring said switch means in accordance with said predetermined interconnect pattern, said slave means controlled by data received from said data manager means;
network master means attached to one of said network ports for controlling the operation of the network, said network master means operable to transmit data to and receive data from said data manager means to establish communication with said video terminals and said slave means, said network master means generating said predetermined interconnect pattern for transmission to said slave means through said data manager means; and
communication link means for interfacing said switch means and said data manager means with said network ports.

8. The video conferencing network of claim 7 wherein each of said remote terminals comprises:
camera means for converting an image to a video signal;
display means for receiving a video signal and converting it to an image;
microphone means for receiving audio information from a transmission medium associated with each of said remote terminals and converting it to an audio signal;
speaker means for receiving an audio signal and converting it to sound information for transmission through said associated transmission medium;
audio/video multiplex means for receiving the locally generated audio and video signals and the audio and video signals from the associated one of said network ports and routing the received signals to either said display means, said speaker means or the associated one of the said network ports; and
control means for controlling said video terminal and the operation thereof and for data interface with said network master means through said data manager means.

9. The network of claim 8 wherein said audio/video multiplex means comprises:
an audio multiplexer for receiving the audio signals from said microphone means and from the associated one of said network ports and for selectively transmitting received audio to either said speaker means or to the associated one of said network ports; and
a video multiplexer for receiving a video signal from said camera means and from the associated one of said network ports and for selectively interconnecting the received video with said display means or with the associated one of said network ports.

10. The network of claim 8 and further comprising preview display means for receiving of video signals from said audio/video multiplexing means and converting the received video to video images, said preview display means having a surface area less than that of said display means.

11. The network of claim 8 wherein said control means is operable to control said video terminal to receive video from the associated one of said network ports and inhibit transmission of Video thereto.

12. The network of claim 8, and further comprising interface means for interfacing with an external local processor for utilizing said external local processor to increase the processing capacity of said video terminals, said interface means operable to receive video signals from said external local processor for input to said audio/video multiplexing means.

13. The network of claim 7 wherein said video terminals operate asynchronously with respect to data communication on the network, said video terminals communicating with said network master means to gain access to other of said video terminals on the network or to allow access from other of said video terminals on the network.

14. The network of claim 7 wherein said predetermined interconnect pattern contains information for said switch means to interconnect select ones of said video terminals in a conference with said switch means receiving video from each of said video terminals in the corresponding conference and transmitting only one of the received video signals to any one of said video terminals in the corresponding conference in accordance with a predetermined priority pattern generated by said network master means, said switch means receiving audio from each of said video terminals in the corresponding conference and summing the received audio for each of said video terminals in the corresponding conference for transmission thereto with the exception of the video generated by the receiving one of said video terminals such that each of said video terminals in the corresponding conference receives only summed audio from the others of said video terminals in the corresponding conference.

15. The network of claim 14 wherein said priority pattern generated by said network master means designates one of said video terminals in the associated conference as a primary video terminal with the video from said primary video terminal received by the remaining of said video terminals in the associated conference and one of said video terminals in the associated conference as a secondary video terminal with the video from said secondary video terminal received by said primary video terminal, the remaining of said video terminals in the associated conference designated as m-ary video terminals, said priority pattern generated only when three or more of said video terminals are in a conference, each of said video terminals operable to transmit a request to said network master means to become said primary video terminal such that said network master means updates the priority status of the requesting one of said video terminals to primary and degrades the status of the prior said primary video terminal to said secondary video terminal and the prior said secondary video terminal to one of said m-ary video terminals.

16. The network of claim 15 wherein each of said video terminals generates the request for primary status in response to receiving voice information from the user of said workstation, said voice being present for a predetermined amount of time.

17. The network of claim 15 wherein each of said video terminals further comprises means for generating a conference lock signal for transmission to said network master means, said network master means inhibiting alteration of said priority pattern upon receipt of said conference lock signal by one of said video terminals such that one of said video terminals generating said conference lock signal has the status thereof updated to said primary video terminal, said status maintained until a signal is received from said primary video terminal to unlock the conference.

18. The network of claim 7 wherein said switch means comprises:
cross point switch means for receiving video and audio information from each of said network ports having one of said video terminals associated therewith and operable to provide access of each of the audio and video signals to each of the remaining of the associated network ports;
video multiplex means associated with each of said network ports associated with said switch means and operable to receive all of the video output signals from said interconnect means for selective output of only one of the received video signals; and
audio multiplex means associated with each of the network ports associated with said switch means and operable to receive all the audio signals output by said interconnect means for summation thereof and output to the associated one of said network ports, said audio multiplex means inhibiting reception and summation of the audio received from the associated one of said network ports;
said audio multiplex means, video multiplex means and said interconnect means controlled by said slave means.

19. The network of claim 7 wherein said data manager means comprises:
first buffer means for receiving data from each of said network ports and storing the received data in one of a plurality of buffers, each associated with one of said network ports for storage of received data;
second buffer means having a plurality of buffers, each associated with one of said network ports for storage of data for transmission to the associated one of said network ports;
said first and second buffer means effecting data communications with the associated one of said network ports for reception of data from or transmission of data to either said video terminals, said network master means or said slave means, said network master means, said slave means and said video terminals operating asynchronously with respect to each other and said data manager means;
memory means for storing a status table having stored therein the status of all of said network ports, the status determining which of said video terminals, said network master means or said slave means is attached thereto; and
central processing means for strobing the buffers in said first buffer means and retriving received data therefrom, the destination of the received data determined by said central processing means and routed to the one of said buffers in said second buffer means for transmission of data therefrom.

20. The network of claim 19 wherein all data received by said data manager means has destination information encoded therein indicitive of the one of said network ports that it is directed towards.

21. The network of claim 19 wherein all of said video terminals, said network master means and said slave means have a predetermined unique identifying code associated therewith and all of the data received by said data manager means has the unique identifier encoded therein, said central processing means associating the unique identifier with information in said status tables such that the received data can be routed to the one of said network ports that the one of said video terminals, said network master means or said slave means having the corresponding unique identifier is associated therewith.

22. The network of claim 19 wherein said slave means is operable to communicate with each of said network ports associated with said data manager means to determine the status thereof and update said status table in said memory means associated with said data manager means.

23. The network of claim 22 wherein said network master means further comprises network master memory means for storage of network status tables indicitive of the status of all of said video terminals associated with said network ports, said network master means updating said network master table with information stored in said data manager status tables to data communication with said slave means, said slave means effecting a transfer of data from said data manager status tables to said network master means for storage in said network master memory.

24. The network of claim 7 and further comprising data manager memory means for storing status tables having information stored therein regarding the status of all of said network ports, said data manager means operable to access said data manager memory means after identifying the destination to which received data is to be routed such that received data can be routed to the correct one of said network ports.

25. The network of claim 24 wherein each of said video terminals has a unique identifier associated therewith and said network master means has a unique identifier associated therewith, said unique identifiers for said video terminals and said network master means stored in said data manager memory means and associated with the one of said network ports that they are attached to.

26. The network of claim 24 wherein said slave means is operable to communicate with each of the devices on said network ports to determine the status thereof, said slave means updating said data manager memory means with status information obtained thereby.

27. The network of claim 26 and further comprising network master memory means for storing said predetermined interconnect pattern and network status information, said network master means communicating with said slave means through said data manager means to retrieve status information from said data manager memory means to update said network master memory means, said slave means accessing said data manager memory means in response to commands from said network master means to transfer status information to said network master means for storage in said network master memory means.

28. The network of claim 7 wherein each of said video terminals further comprises means for initiating a conference with another of said video terminals in the network, said accessing means operable to generate a message directed to said network master means requesting a conference with a predetermined one of the remaining of said video terminals in the network, said network master means effecting a conference in response to a request from one of said video terminals.

29. The network of claim 28 wherein said network master means further comprises means for generating a message directed toward the one of said video terminals to be placed in conference with the accessing one of said video terminals, said video terminals further comprising means for responding to a request from said network master means to be placed in a conference with the accessing one of said video terminals such that the said network master means is a apprised of the status of the requested one of said video terminals, said network master means communicating with said slave means after receiving said response from the requested one of said video terminals to reconfigure said switch means to provide an audio and video path from the requesting one of said video terminals to the requested one of said video terminals.

30. The network of claim 29 wherein each of said video terminals comprises means for selectively inputting or outputting audio and video information to the data link effected by said network master means.

31. The network of claim 29 wherein each of said video terminals further comprises means for outputting an audible signal on the audio path effected by said network master means when said video terminal is the requested one of said video terminals such that the requesting one of said video terminals can receive an audio feedback indicitive of a completed audio path.

32. The network of claim 31 and further comprising means for outputting an audible signal to the user at the requested one of said video terminals to indicate that an audio and video path has been provided to a requesting one of said video terminals in the network such that the user of the requested one of said video terminals is apprised of the request.

33. The network of claim 29 wherein each of said video terminals further comprises means for accessing the video transmitted from the requesting one of said video terminals prior to transmitting video therefrom such that the user is allowed to preview the video from the requesting one of said video terminals prior to transmitting video thereto.

34. The network of claim 7 wherein said network master means further comprises means for controlling each of said video terminals to enter a hold mode, said video terminals in the hold mode looping back the transmitted video therefrom for reception thereof such that the user of said video terminal in the hold mold receives there transmitted vided.

35. The network of claim 34 wherein the loop back video is looped back internal to said video terminal in the hold mold such that it is not transmitted to the said switch means for processing thereby.

36. The network of claim 7 wherein said communication link means comprises:
a transmission medium associated with each of said network ports for carrying audio, video and data between said switch means, said data manager means and said network port;
first interface means disposed at said network ports for interfacing between the devices attached to said network ports between said transmission medium; and
second interface means disposed at the other end of said transmission medium for interfacing between said transmission medium and said data manager means and said slave means;
said first interface means receiving audio, video and data from the device associated with said network port and encoding it for transmission along a first path in said transmission medium, said first interface means receiving and decoding from a second path in said transmission medium encoded audio, video and data for transmission to the associated one of said network ports; and
said second interface means receiving and decoding encoded data from said first path in said transmission medium for transmission of said decoded audio and video to said switch means and said decoded data to said data manager means, said second interface means receiving data from said data manager means and audio and video from said switch means and encoding the received audio, video and data for encoding thereof and transmission on said second path in said transmission medium;
said first and second paths in said transmission medium isolated to allow full duplex communication.

37. The network of claim 36 wherein said transmission medium comprises a coaxial cable and said first and second interface means encode audio, video and data through frequency division multiplexing techniques.

38. The network of claim 36, wherein said transmission medium further comprises:
a third path isolated from said first and second path for carrying information therealong;
said first interface means interfacing with said third path and with a peripheral network device, said peripheral device operating independent of the video conferencing network; and
said second interface means interfacing with said third path and with a peripheral network, said peripheral network operating independent of the video conferencing network such that said peripheral network device and said peripheral network utilize said transmission medium and operate in parallel with the video conferencing network and independent therefrom.

39. The network of claim 36 wherein transmission of data along said first and second paths in said transmission medium is asynchronous such that said data manager means and the device attached to said network ports communicate asynchronously.

40. The network of claim 7 wherein said communication link means comprises:
a first transmission medium disposed between said network port and said switch means and having a first path and a second path, said first path for carrying audio and video from said network port to said switch means and said second path for carrying audio and video from said switch means to said network port;
first audio/video interface means for encoding audio and video from said network port for transmission along said first path and receiving encoded audio and video from said second path for decoding thereof at said network port;
second audio/video interface means for receiving encoded audio and video from said first path for decoding and routing to said switch means and for receiving audio and video from said switch means for encoding thereof and transmission along said second path;
a second transmission medium disposed between said data manager means and said network port for data transmission;
first data interface means for interfacing data communications between said network port and said second transmission medium; and
second data interface means for interfacing between said second transmission medium and said data manager means.

41. The network of claim 40 wherein said second transmission medium provides a first and second path for data transmission, said first path transmitting data from said network port to said data manager means and said second path transmitting data from said data manager means to said network port such that a full duplex data path is provided.

42. The network of claim 40 wherein said second transmission medium comprises a local area network.

43. The network of claim 40 wherein said first transmission medium is comprised of a broadband multichannel communication link for transmission of encoded audio and video and said first and second audio/video interface means comprise audio/video modems for modulating and demodulating audio and video onto a particular one of the channels in said broadband link, each of said audio and video modems selecting one channel for transmission of encoded audio and video and one channel for reception of audio and video.

44. The network of claim 43 wherein said audio/video modems are operable to transmit or receive audio and video from any of the channels in said broadband link, said audio/video modems controlled by said network master means to determine the channel over which audio and video is to be transmitted or received from.

45. The network of claim 7 wherein said communication link means associated with said network master means carries data only and is comprised of:
a transmission medium for transmitting data;
first data interface means disposed between said transmission medium and said data manager means for interfacing data communications therebetween; and
second data interface means connected between said network master means and said transmission medium for interfacing data communications therebetween.

46. The network of claim 45 wherein said transmission medium comprises a local area network.

47. The network of claim 7 and further comprising:
data manager memory means for storing status information for all of said network ports, said data manager means accessing said data manager memory means to determine which of said ports correspond to the identification information in the received data, the received data routed to the corresponding one of said network ports;
said slave means communicating with said network ports to determine status thereof from response information received from said video terminals or said network master means attached to said network ports, said slave means operable to update the status of said data manager memory means; and
network manager memory means for storage of network status information, said network master means communicating with said slave means through said data manager means to control said slave means to access said data manager memory means to transfer data therefrom for storage in said network master memory means to update the status contained therein.

48. The network of claim 47 wherein:
said data manager means comprises a plurality of secondary data manager means, each of said secondary data manager means associated with a predetermined number of said network ports for receiving data therefrom and transmitting data thereto, each of said data manager means interfaced with the one of said network ports associated with said network manager means; and
said data manager memory means comprise a plurality of secondary memory means each associated with one of said secondary data memory means for storing status information for only the ones of said network ports as interfaced with the associated one of said secondary data manager means.

49. The network of claim 48 wherein said slave means is comprised of a plurality of secondary slave means each associated with one of said secondary data manager means and the associated one of said secondary memory means; and
said switch means comprises a plurality of secondary switch means each associated with one of said secondary data manager means and for receiving audio and video from each of said network ports interfaced with the associated one of said secondary data manager means and interconnecting the received audio and video for transmission to select ones of said network ports in accordance with said predetermined interconnect pattern, each of said secondary switch means interfaced with each of the remaining ones thereof for transfer of audio and video information therebetween;
said secondary slave means controlling the configuration of the associated ones of said secondary switch means.

50. The network of claim 48 wherein said network master means comprises a plurality of secondary network master means, each associated with one of the associated network ports of said secondary data manager means;
said secondary network master means having a predetermined priority such that only one of said secondary network master means is operable at any given time; and
means for activating the next sequential one of said secondary network master means in the priority scheme when the highest priority one of said secondary network master means is removed from the network.

51. A method for effecting a video conference between remote network ports, comprising:
disposing a video terminal at each of the remote points, each of the video terminals generating output audio and video and receiving input audio and video information, each of the video terminals transmitting receiving data;
interconnecting the audio and video inputs and outputs of select ones of the video terminals in accordance with a predetermined interconnect pattern;
receiving data from the network ports at a central routing device, identifying destination of the data and routing the data to the corresponding destination;
controlling the interconnection of video terminals from one of the ports by establishing data communication therewith, data generated at the controlling point routed through the central routing device to the destination port and data received from the routing device having the controlling port as its destination, the predetermined interconnect pattern generated at the controlling device; and
controlling the interconnection of the audio and video inputs and outputs of the select ones of the video terminals at a slave port by receiving the interconnect pattern at this slave port from the controlling port through the routing device.

52. The method of claim 51 wherein the step of generating the output audio and video signal comprises sensing an image and converting the image to a video signal and receiving audio information from a transmission medium associated with each of the terminals and converting it to an audio signal in the step of receiving audio and video information comprises receiving the video signal and converting it to an image for display and receiving the audio signal and converting it to sound information for transmission through the associated transmission medium.

53. The method of claim 51 and further comprising selectively inhibiting transmission of video from a select one of the video terminals while receiving video from another of the video terminals that is selectively interconnected therewith.

54. The method of claim 51 wherein data communication between the controlling port and video terminals and the slave port is asynchronous.

55. The method of claim 51 wherein the interconnection of video terminals is controlled to place select ones of the video terminals in a conference with all of the video of each of the video terminals received at a central switching point and only one video transmitted from the central switching point to each of the video terminals in accordance with a predetermined priority pattern generated at the controlling port and receiving audio from each of the video terminals at the central switching point that are in the conference and summing the received audio for each of the video terminals in the conference for transmission thereto with the exception of the video generated by the receiving one of the video terminals such that each of the video terminals in the conference receives only summed audio from the other video terminals in the conference.

56. The method of claim 55 wherein the priority pattern generated at the controlling designates one of the video terminals in the conference as a primary video terminal with the video from the primary video terminal received by the remaining of the video terminals in the conference and one of the video terminals in the conference as a secondary video terminal with the video from the secondary video terminal received by the primary video terminal, the remaining of the video terminals in the conference designated as m-ary video terminals, the priority pattern generated only when three or more of the video terminals are in a conference, each of the video terminals operable to transmit a request to the controlling port to become the primary video terminal such that the controlling port updates the priority status of the requesting one of the video terminals to primary and degrades the status of the prior primary video terminal to the secondary video terminal and the prior secondary video terminal to one of the m-ary video terminals.

57. The method of claim 56 and further comprising generating a request for primary status at each of the video terminals in response to receiving voice information that exceeds a predetermined threshold from the user of the video terminal, the voice signal exceeding the predetermined threshold for a predetermined amount of time.

58. The method of claim 56 and further comprising generating a conference lock signal at one of the video terminals for transmission through the central routing device to the controlling port, the controlling port inhibiting alteration of the priority pattern upon receipt of the conference lock signal such that the video terminal generating the conference lock signal has the status thereof updated to the primary video terminal, the status maintained until the signal is received from the primary video terminal to unlock the conference.

59. The method of claim 51 the step of receiving and routing the data at the central routing device comprises:
receiving the data from each of the network ports and storing it in one of the plurality of buffers, each buffer associated with one of the network ports for storage of received data;
identifying the port to which the data stored in the received buffers is to be routed;
routing the identified data to one of a plurality of output buffers, each buffer associated with one of the network ports for storage of output data for transmission thereto;
step of receiving data for storage in the receiving buffers and the step of transmitting data from the output buffers effected by asynchronous communication between the network ports;
storing a status table having stored therein the status of all of the network ports, the status determining whether the network port associated with the video terminal, a controlling port or a slave port;
the step of determining the destination from the received data determined in accordance with the information stored in the status table.

60. The method of claim 59 wherein the data received and stored in the received buffer has destination information encoded therein indicitave of one of the network ports that it is directed towards.

61. The method of claim 59 wherein all the video terminals, the controlling port and the slave port have a predetermined unique identifying code associated therewith and all the data received at the central routing point has a unique identifier encoded therein, the unique identifier decoded from the data and associated with information in the status table such that the received data can be routed to the appropriate one of the network ports having the unique identifier associated therewith.

62. The network of claim 59 and further comprising storing network status tables at the controlling port indicitive of the status of all of the video terminals associated with network ports, the controlling port updating the network status tables with information stored in the data routing status tables without a controlling port to control the network from information stored in network status tables.

63. The network of claim 51 and further comprising:
initiating a conference at each of the video terminals by generating requests data for the controlling port and transmitting the request data thereto, the controlling port operable to generate a request message and direct it to the destination port to request access thereto, the video terminal at the network port receiving the request data generating response data and transmitting it to the control port to indicate status thereof, the control input operable to interconnect the access requesting video terminal and the requested video terminal if the response of the requested video terminal is appropriate in accordance with a predetermined protocol.

64. The method of claim 63 and further comprising generating an audible ring back signal at the requested video terminal prior to receiving audio or video from the interconnection effected by the controlling port such that the requesting video terminal is provided audio feed back.

65. The method of claim 64 and further comprising generating an audible signal at the requested one of the video terminals in response to the controlling port effecting an audio and video communication path to the requesting one of the video terminals such that the user is apprised of the interconnection, audio and video transmission from the requested video terminal inhibited from being transmitted over the audio and video interconnection.
Description
TECHNICAL FIELD OF THE INVENTION

The present invention pertains in general to communication networks and, more particularly, to communication networks for interfacing between remote video terminals to provide video, audio and data paths therebetween.

CROSS REFERENCE TO RELATED APPLICATION

This application is related to patent application Ser. No. 720,507 filed Apr. 5, 1985, and U.S. patent application Ser. No. 721,083 filed Apr. 18, 1985.

BACKGROUND OF THE INVENTION

Video communication has evolved over the years from a simple video telephone concept to a sophisticated network for allowing multiple parties to enter into a video conference. A number of factors have prevented total success of such prior video systems, including public acceptance, excessive cost, system complexity and inadequate video quality. Although these factors can be manipulated somewhat to provide an improved system for video communications, inherent constraints such as standardized video formats and presently existing communications systems minimize the design flexibility which may be utilized in achieving a feasible system.

Video communications can be utilized for a number of applications. In some applications, only transmission of a hard copy is required, such as a picture or graphics representation. Such hard copy transmission is normally accomplished by such techniques as facsimile transmission to enable transmission of such things as x-rays, flow charts, and the like. However, for a full video conferencing system wherein individuals desire both an audible communication path and a real time visual communication path, it is necessary to provide full motion color video. The transmission of full motion color video normally requires a much greater bandwidth than the transmission of facsimile data. This is due to the fact that the video is transmitted in "real time" to allow an interactive conference.

Non real time video systems have been previously developed for teleconferencing which operate on lower bandwidth communication links. One type of non real time system is often referred to as the slow scan video system which is programmed to send new pictures at regular intervals, whether the image is changed or not. In this type of system, movement is prohibited in order to provide a relatively clear picture. An alternate to the slow scan system is the freeze-frame system which records a clear picture of the speaker and transmits this clear picture to the remote terminals in the conference at regular intervals. However, the slow scan and freeze-frame systems are not real time and the parties viewing the conference are only provided a sequence of stepped poses for the speaker.

Full motion video, heretofore the most preferred for video conferencing, is accomplished by a number of techniques. The most effective full motion video conferencing systems transmit over 1.544-megabits/s T1 telephone lines. Although the picture quality on these high bandwidth systems is high, so are the operational costs per hour for nationwide point-to-point connections.

To decrease the cost, data compressed video conferencing systems have been developed which operate on a 56-kb/s packet-switched network. Data compression is required to operate on these 56-kb/s systems, since direct digitization of standard NTSC broadcast video color signals requires approximately 80 megabits per second, far beyond the capacity of most transmission lines. To transmit full-motion color at lower bandwidths, the digital signal must be compressed by the removal of redundant information.

Two main data compression approaches have been heretofore developed, namely interframe coding and intraframe coding. In interframe coding, successive video frames are compared, pixel by pixel, and only changed values are transmitted. In intraframe coding, values for entire blocks of pixels within a frame are transmitted as mathematical transforms. These techniques are useful for transmitting at 1.544-Mb/s over T1 lines. However, transmission at 56-kb/s requires further data compression. This is accomplished by squeezing out data on luminescence, hue, resolution and scan rate. A cosine transform is utilized to compress the data efficiently, with the negative result being breakup of the picture into blocks of pixels when the transform needs time for each recalculation and the system has too many bits to send. Other prior 56-kb/s systems use a binary algorithm that degrades by losing resolution when overwhelmed by too much motion.

The disadvantages to the 56-kb/s systems and similar digital systems are that they first require the availability of a digital network and, secondly, they require a relatively expensive codec to interface between the video terminal and the network. These systems are seldom available or financially feasible for local or intrafacility use.

In prior video conferencing systems, another major disadvantage has been the initial cost of the remote terminals which are, at present, dedicated to video conferences. The longer a video terminal remains idle, the higher the cost-per-hour. Therefore, it would be desirous to integrate the remote video terminal with other functions to lower the effective cost per hour of the video conferencing feature.

In view of the above disadvantages of prior video conferencing systems, there exists a need for a full motion, color video conferencing network that overcomes the deficiencies of the present systems and is more adapted to economical local and intrafacility use.

SUMMARY OF THE INVENTION

The present invention disclosed and claimed herein comprises a video conferencing network for providing video, audio and data communication between remotely disposed video terminals. Each of the video terminals transmits and receives video, audio and data information through the network. The network includes a centrally disposed switching network for receiving audio and video information on one of a plurality of audio/video ports and selectively interconnecting this information to one or more of the remaining audio/video ports. This interconnection provides an audio and video path between two or more of the video terminals. A centralized controller is in data communication with each of the video terminals and the switching network and controls the configuration of the switching network to provide the appropriate audio and video paths in response to data received by the controller from the video terminals. A communication link is provided for interconnecting each of the video terminals with one of the audio/video ports of the switching network for audio and video transmission. The communication link also provides a data link between the video terminals and the controller.

The communication link is comprised of a single coaxial cable disposed between each of the video terminals and the switching and control networks. Audio and video is transmitted to the switching network and data is transmitted to the controller, with the audio, video and data being transmitted by frequency division multiplexing. At the video terminal end of the coaxial cable, a multiplex/demultiplex circuit is provided for distinguishing between transmitted and received audio, video and data by receiving the audio, video and data and multiplexing it onto the cable and receiving the multiplexed data from the cable and demultiplexing it for processing by the associated video terminal. A second multiplex/demultiplex circuit is provided at the other end of the coaxial cable for receiving transmitted data from the coaxial cable and demultiplexing the received audio, video and data for processing by the switching network and the controller and also multiplexing audio, video and data for transmission on the cable.

In yet another embodiment of the present invention, the controller is comprised of a Network Master, a Slave and a Data manager. The Network Master processes the data received from the video terminals and generates configuration data in response to the processing of this data. The configuration data contains information for configuring the switching network. The slave receives the configuration data and configures the switching network in response to receiving the configuration data. The data manager has a plurality of data ports for receiving data from each of the video terminals and the Network Master and routing the received data from the video terminals to the Network Master and the reconfiguration data to the slave.

The slave generates messages for transmission to the video terminals, the messages directed to the data manager for determination of which of the data ports the generated messages are to be transmitted from. After making this determination, the data manager routes the messages from the slave to each of the video terminals and the video terminals generate messages for transmission back to the slave in response to receiving the slave messages. The data manager receives these messages and routes them to the slave, the data manager making a determination that the messages are directed toward the slave. These messages have encoded therein unique IDs that correspond to the devices such as the video terminals or, the slaves or the Network Master.

The communication between the slave and the video terminals provides status information of the devices attached to the data ports. This status information is stored in an internal storage medium associated with the slave and is periodically updated in order to maintain Network status.

The Network Master also communicates with the slave by generating the status messages for transmission to the data manager and routing to the slave. These messages request status information from the slave, which information is encoded into a message and transmitted to the buffer manager for routing to the Network Master. This status information is stored in an internal storage medium associated with the Network Master. Therefore, the Network Master contains a separate status table apart from the status information stored by the slave.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying Drawings in which:

FIG. 1 illustrates a diagrammatic view of the Mate remote video terminal and work station combination;

FIG. 2 illustrates a schematic block diagram of the Mate remote video terminal;

FIG. 3 illustrates a cluster of Mate video terminals connected together in the basis switching network;

FIG. 4a illustrates a schematic block diagram of the Mix switching network;

FIG. 4b illustrates the communication paths for the audio/video/data video conferencing information and parallel baseband information;

FIG. 5 illustrates a diagram of the transmission spectrum for the single cable multiplexing format utilized for communication between the Mix switching network and the Mate video terminals;

FIG. 6 illustrates a schematic block diagram of the single cable multiplexer;

FIG. 7 illustrates a network of Mate video terminal clusters;

FIG. 8 illustrates a video conferencing network utilizing a baseband network for interfacing data to the video terminals with a broadband network for interfacing audio and video therebetween;

FIG. 9 illustrates a broadband network for interfacing video, audio and data thereover with a centralized controller provided for data interface;

FIG. 10 illustrates a satellite link between networks;

FIG. 11 illustrates a block diagram of the interface between the Mate video terminal and the broadband network;

FIG. 12 illustrates a block diagram of the audio video processor portion of the Mate;

FIG. 13 illustrates a diagrammatic view of the audio path with gain switching;

FIG. 14 illustrates a diagrammatic view of the audio patch for a multiway conference with gain switching;

FIGS. 15a and 15b illustrate graphs of the switched gain for the audio paths;

FIG. 16 illustrates a block diagram for the Mix switching network processor;

FIG. 17 illustrates a block diagram of the interface board for the remote video terminal;

FIG. 18 illustrates a schematic of the interface network for interfacing the video terminal with a local processor;

FIG. 19 illustrates a schematic for the audio video processor portion of the Mate;

FIGS. 20a-20b illustrate schematics for the Mix switching network processor;

FIG. 21 illustrates a flowchart for placing and receiving a call at the Mate remote video terminal;

FIG. 22 illustrates a flowchart for adding a party to a video conference at the Mate remote video terminal;

FIG. 23 illustrates a flowchart for locking a conference onto the Mate remote video terminal;

FIG. 24 illustrates a flowchart for generating the voice detect signal;

FIG. 25 illustrates a schematic block diagram of task scheduling in the Mix switching network;

FIG. 26 illustrates a diagrammatic view of the video conferencing network showing a switch plane and a data plane;

FIG. 27 illustrates a side view of the diagram of FIG. 26 with an alternate configuration for the Network Master;

FIG. 28 illustrates a diagrammatic view of the data plane for a three mix network;

FIG. 29 illustrates a flowchart for the master task in the network for placing a call;

FIG. 30 illustrates a flowchart for the master task when adding a party to the conference;

FIG. 31 illustrates a flowchart for determining the priority of parties in a conference in the master task of the network;

FIG. 32 illustrates a flowchart for the keep alive function between the master and slave tasks in the switching networks; and

FIG. 33 illustrates a flowchart for communication between the master and slave tasks in the switching network.

DETAILED DESCRIPTION OF THE INVENTION

Multifunction Work Station

Referring now to FIG. 1, there is illustrated a diagrammatic view of a multifunction work station. The work station includes a video terminal 10 which includes a monitor display screen 12 and a viewfinder or secondary display screen 14 for displaying video. The video terminal 10 is hereinafter referred to as "Multimedia Terminal Equipment" or "Mate". The Mate 10 is utilized for processing audio and video information and also data. The audio/video/data can be output to a video communication network through a single cable 16 to interface with other Mates at remote points. The audio/video/data is multiplexed onto the cable 16 which is hereinafter referred to as the "SCM cable". In this mode, the Mate 10 can comprise a portion of a video communication network which can be connected in a video conferencing mode, as will be described hereinbelow.

The Mate 10 interfaces with the user through a station set interface box (SSIB) 18 through a serial data link 20. The SSIB 18 includes an integral key pad for allowing the user to input data thereto in the form of key strokes. In addition, a standard telephone 22 with its associated key pad can be interfaced to the Mate 10 through an interface box 24. In the preferred embodiment, the interface box 24 may be integrated with the SSIB 18 such that the telephone 22 may plug into the SSIB 18. Hereinafter, the interface box 24 will be considered a part of the SSIB 18.

The Mate 10 includes internal thereto a video camera 32 for generating a local video signal. In addition, an external camera 26 can be interfaced to the Mate 10 as well as other auxiliary audio/video devices such as a video recorder (VCR) 28. As will be described hereinbelow, the video from either the internal video camera or the auxiliary devices 26 and 28 can be utilized to either display video on the monitor 12, the viewfinder 14 or generate a video signal for transmission on the SCM cable
16.

The internal camera 32 shoots color television images using a fixed focus wide angle lens. A microphone 34 is mounted on the front panel of the Mate 10 to allow audible interaction between the user and the Mate 10. The video displayed on the monitor 12 is controlled by a mode switch 36, the operation of which will be described hereinbelow. Indicators 38 are provided to determine when video is being transmitted over the SCM cable 16 when power is applied and also when a privacy mode is selected. The privacy mode is enabled through a privacy switch 40. A mode switch 41 is also provided that enables the user to select various functions of the Mate 10 in a sequential manner, as will be described hereinbelow.

The Mate 10 is operable to interface with a local processor 42 through an interface circuit 44. A keyboard 46 is provided which is interfaced to the local processor 42. In the preferred embodiment, the type of local processor 42 utilized requires the keyboard 46 to interface through a separate monitor. Since the Mate 10 serves as the interface monitor, the interface circuit 44 provides this interface in addition to interfacing the video and data output of the local processor 42 with the Mate 10. When the local processor 42 is utilized, the Mate 10 can operate in the Slave mode and act as the monitor for the local processor 42. In the Slave mode, the local processor 42 controls the majority of the functions of the Mate 10 wherein the Mate 10 operates as a monitor with the additional capability of maintaining contact with the network through the SCM cable 16. The interface circuit 44 is dependent upon the type of local processor 42 utilized and is designed for each specific local processor.

The local processor 42 interfaces its video and data through a line 45 to the interface box 44. The video is normally in the form of three signals constituting the red, green and blue signals that drive the monitor and also the vertical and horizontal sync signals. The data is normally comprised of some form of standardized serial link such as an RS-232 format. This data link can contain both control data and also audio data in the form of synthesized sounds etc.

Local processors or other peripheral equipment which are utilized in conjunction with the Mate 10 to form the overall workstation normally include the capability to interface with a baseband network such as a local area network (LAN). The network of the present invention accommodates transmission of baseband information which is dedicated to operation of the local processor 42 in a separate and distinct network from that for video conferencing by allowing transmission of baseband information over the SCM cable 16. The local processor 42 is interfaced with the interface box 44 through a baseband transmission line 47 which is internally coupled to the SCM cable 16. The audio/video/data that corresponds to the video conferencing network is separate and distinct from the baseband information that is transmitted and received by the local processor 42. In this manner, only a single cable is required to accommodate both a video conferencing network and also maintain the baseband communication link, which is inherent to most localized facilities. In this manner, the video teleconferencing feature can be added to an already existing LAN system with the operation of both systems remaining separate and distinct.

Referring now to FIG. 2, there is illustrated a schematic block diagram of the Mate 10. All of the data processing in the Mate 10 is performed by a Central Processing Unit (CPU) 48. The CPU 48 carries out video and audio switching and controls audio levels in the Mate 10. The processor has three 9600 baud serial ports that direct the actions of the Mate 10 such that the functions thereof can be directly or indirectly controlled by external devices communicating through these ports. Programs utilized by the CPU 48 are stored in a memory 50 which is comprised of both volatile and nonvolatile memory. The SCM cable 16 is connected to the input of a single cable multiplexer (SCM) 51 that both transmits and receives data on the SCM cable 16 and interfaces with a data port, a video port and an audio port. There is a separate port for data input, video input and audio input and a separate port for data output, video output and audio output. As will be described hereinbelow, the audio/video/data is modulated onto a first RF carrier for transmission from the Mate 10 and demodulated from a second RF carrier for received audio/video/data. The baseband information is input to the SCM 51 and trasmitted over the SCM cable 16 at baseband for normal baseband communication.

The video signals from the VCR auxiliary device 28, the SCM 51 and the internal camera 32 are input to a video switch 52 for selective connection to the various outputs of the Mate 10. One switched output is connected to the viewfinder 14, one output is connected to the video input of the SCM and another output is provided for connection to an auxiliary circuit labeled AUX. A fourth output is provided for connection to the input of a decode circuit 56 which has its output connected through a switch 58 to the monitor 12. The decoder 56 is operable to decode the video transmitted through the video switch 52 into a format compatible with the operation of the monitor 12. In the preferred embodiment, the monitor 12 operates in a "RGB" mode requiring only information regarding the red, green and blue color levels with the addition of horizontal and vertical sync, whereas the video switch 52 is operable to process video in a format that complies with RS-170 NTSC levels. However, depending upon the decoder that is used, other types of video can be processed by the video switch 52 as long as the viewfinder 14 is compatible therewith. The switch 58 is operable to switch between the local processor 42 and the decoder 56. Although the local processor 42 could be processed by the video switch 52, the preferred embodiment utilizes the interface circuit 44 in FIG. 1 to reformat the output of the local processor 42 into the RGB format. Therefore, when video is received from the local processor
42, the switch 58 is activated to apply the appropriate video signals to the monitor 12. The video switch 52 is controlled by the CPU 48.

An audio switch 54 is provided for receiving the audio output of the SCM 51, a synthesized sound output from the CPU 48 labeled "Sound Gen", an auxiliary input labeled AUX and the audio output of the SSIB 18. The microphone 34 is also interfaced with one input of an audio switch 54 through a voltage controlled amplifier (VCA) 59. The microphone 34 is controlled by a switch 55 which can selectively disconnect the microphone 34 from the input of the VCA 59. A similar switch 53 is provided for selectively disconnecting the SSIB 18 from the circuit. The microphone 34 and the SSIB 18 are never connected at the same time.

The audio switch 54 can route any of the inputs to either an auxiliary output labeled AUX or to the audio input of the SCM 51. A third output is connected to the input of a VCA 60, the output of which is connected to the audio input of the SSIB
18. The output of the VCA 60 is also connected through a mute switch 62 to the input of a speaker 64. The VCA's 59 and 60 are controlled by the CPU 48 to determine the gain of both the input audio and the output audio. As will be described hereinbelow, there is no cross coupling of audio in the Mate 10 during a video conference. This allows the VCA's 59 and 60 to separately control the outgoing audio level and the incoming audio level, thus providing local control of the round trip audio path, as will be described in more detail hereinbelow. The various connections of the audio switch 54 are controlled by the CPU 48.

Switched Rate Monitor

The monitor 12 is an analog input, 135 volt color RGB monitor that has the capability to accept two horizontal rates. It operates at a first rate for displaying NTSC rate video, thus operating at a horizontal rate of 15.73426 Hz and a vertical rate of 59.94 Hz. This horizontal rate requires a horizontal blanking interval of 10.9 microsec. The vertical blanking interval is 1.27 msec. Although the rate matches standard NTSC, the video supplied to the monitor will be RGB plus composite sync, RS-178 levels.

The monitor 12 operates at a second rate to provide it with a capability of displaying computer generated data which could conceivably originate from a variety of different local processors or computers. These computers typically generate data with a horizontal rate from 15.73426 Hz to 31.5 Hz with a vertical rate ranging from 45 Hz to 60 Hz. However, each different computer generates data at only one horizontal and vertical frequency, thereby only requiring one additional scanning rate in addition to the standard NTSC rate. The video supplied to the monitor is the same format as for the NTSC rate video; that is, RGB at the RS-170A level (1.0 volt peak to peak) but the sync could be separate horizontal and vertical syncs.

NTSC video has a composite sync associated with it which is a composite of horizontal and vertical sync. Computers usually have separate horizontal and vertical outputs. In order to be able to display either type of data on the monitor requires the ability to use either type of sync. A signal is output from the CPU 48 to control the type of sync that the monitor 12 will receive. In one mode, composite syncs will be utilized and in the second mode, separate horizontal and vertical syncs are present on respective inputs.

There are five inputs associated with the video input of the monitor 12. Three of them are the RGB video inputs, one for red, one for green and one for blue, and the other two inputs are horizontal sync and vertical sync. When composite sync is utilized, it will be present on the vertical sync input and the horizontal sync input will be ignored.

NTSC video expects a ten percent horizontal and vertical overscan of the cathode-ray tube (CRT). Computer generated data frequently does not require overscanning of the CRT and, in fact, some data would be lost if overscanning were used. The monitor 12 provides a control line input from the CPU 48 to allow selection of an overscanning mode when necessary. The amount of overscanning is adjustable by an internal control in the monitor 12. Overscan is defined as the raster being larger than the face of the CRT.

When switching from one video source to another in the Mate 10, there will be a finite amount of time before the monitor acquires sync and the picture stabilizes. This time is minimized, but it is not reduced to zero. To make the switch appear less obtrusive to the viewer, the video is ramped down quickly before the switch is made. The video is then ramped back up after a specified amount of time has elapsed. This process usually occurs in less than 0.5 seconds. A monitor which will provide the switchable scanning frequencies is manufactured by Victor Company of Japan, Ltd., part No. SD-H2114DP.

Mate Master/Slave Operations

In operation, the Mate 10 can operate in a Master or Slave mode. It services either the local processor 42, the SSIB 18 or the network. In the Master mode, the Mate 10 is utilized to select data and audio from the SSIB 18 and execute instructions in response thereto. The SSIB 18 is utilized to allow a user to enter keystroke instructions to the Mate 10 to perform such functions as determining whether video should be displayed on a monitor 12 or the viewfinder 14 and deciding where the video is to be received, i.e., the local processor, the auxiliary port, the camera port or the network. Additionally, keystrokes can be input on the SSIB 18 to input unique identifiers (ID's) of other remote terminals or work stations for initiating a video conference therebetween, as will be described hereinbelow.

In the Slave mode, the Mate 10 accepts input only from the local processor and passes through all other communications. It serves as the audio and video input/output and communications terminal for the application program running in the local processor. In this mode, the Mate passes messages received from the SSIB 18 to the local processor and only switches in response to receiving a command from the local processor. By providing for a separate local processor, a more versatile remote terminal is provided. This allows for a given remote terminal to be compatible with already existing equipment in an office.

For example, if one office utilizes a local processing system of a first type and a second office utilizes a local processing system of a second type, both processing types can be interfaced to the Mate 10 merely by selecting a different interface circuit 44. In this manner, both the type and the size of the local processor 42 can vary and still be accommodated by the Mate 10. When utilized with a separate local processor 42, the Mate 10 provides the necessary processing capability to further extend the versatility of the remote terminal, in that the Mate 10 enables the local processor 42 to interact with the network. However, only the Mate can initiate and maintain a communication link with the network. The local processor 42
cannot directly communicate with the network but, rather, it requests the Mate to communicate for it.

First Level Conferencing Network

Referring now to FIG. 3, there is illustrated a diagrammatic view of the simplest form of a video conferencing network which is designated as a First Level Conferencing Network. This network is comprised of a central switching network 66
referred to as a Multimedia Information Exchange (hereinafter referred to as Mix). The Mix 66 has six ports connected to six Mates 10 labeled "01", "02", "03", "04", "05" and "06" through associated SCM cables 16. However, the Mix 66 could be connected to additional Mates 10, depending upon the internal configuration thereof. In the preferred embodiment, the Mix 66 is interfaced with eight Mates 10, but for simplicity purposes, only six Mates 10 are illustrated.

Internally the Mix has a full nXn crosspoint switch for the audio and video paths of each port, n being equal to the number of Mates interfaced with the Mix. Each switch is independently controllable to provide nonblocking operation. A serial data control path is associated with each Mate 10 and these are routed independently to a control processor internal to the Mix 66.

Two Way Conference

In operation of the configuration shown in FIG. 3, the Mix 66 is in communication with each of the Mates 10 on the network through a serial data path in the SCM cables 16. Upon receiving a request from any of the Mates 10 to place a call to another Mate in the network, the Mix 66 determines if that Mate is available and, if so, "places the call." The call is placed by providing a video and an audio path between the two Mates 10 in the conference. The basic procedure for placing a call is to first send a message to the Mix 66 requesting a call. This message contains information regarding both the ID of the originating Mate and also the ID of the destination Mate and is transmitted along the data path. The Mix 66 then acknowledges to the originating Mate that it has received this information and then determines if a path is available to the destination Mate. This is determined from an internal status table which the Mix 66 maintains such that the status of all Mates on the network is known.

If a line is available, the Mix 66 then determines if the destination Mate is "busy". If so, the originating Mate is notified by an appropriate message. If the destination Mate is not busy, a message is sent from the Mix 66 to the destination Mate indicating that there is an incoming call. Prior to sending of the incoming call message, the switch connection is made to provide a video and audio path between the originating and destination Mates. The destination Mate then provides a ringback signal to the originating Mate to indicate that it is locally outputting an audible ring or "chime". When the call is received by inputting an appropriate key stroke at the destination Mate, video and audio is received by the destination Mate and, simultaneously, video and audio is transmitted from the destination Mate. The video and audio path provided by the SCM cable 16 and the Mix 66 is a full duplex two-way path wherein both paths are isolated such that there is no cross-coupling between video or audio. This isolated two-way transmission is provided by a frequency division multiplexer, as will be described hereinbelow.

Multi-Way Conference

To connect more than two Mates in the system shown in FIG. 3 together in a video conference, it is necessary for an originating Mate to first place a call with a destination Mate and then place this destination Mate on hold and contact another Mate. For example, if Mate 01 wishes to set up a video conference with Mates 04 and 05, a call is first placed to destination Mate 04, as described above. A hold signal is then transmitted from the originating Mate 01 to the Mix 66. Upon receipt of this hold signal, a message is sent to destination Mate 04 to place it on hold. Destination Mate 04 then "loops" back the internal video such that the party at the destination Mate 04 receives his own video transmission. A call is then placed to destination Mate 05 and a two-way conference initiated. This two-way conference between originating Mate 01 and destination Mate 05 is maintained and destination Mate 04 maintained on hold until a message is sent from the originating Mate 01 to the Mix
66 to bring all the parties back into the conference. A conference table is maintained internal to the Mix 66 to determine which Mates are a part of the conference.

During a video conference, each Mate receives audio from all of the other Mates in the conference, this audio being summed at the Mix 66. Each Mate's own audio is not summed to prevent feedback. However, only one video transmission can be made from the Mix 66 to any of the Mates. The video that is displayed on any of the monitors 12 of the Mates 10 in the conference is determined by a priority system, which will be described in detail hereinbelow.

Mix Switching Network

Referring now to FIG. 4a, there is illustrated a block diagram of the Mix 66 of FIG. 3. Each of the input ports are connected to one of the SCM cables 16 and are interfaced to a separate SCM module 68 labeled "SCM 01" through "SCM 08", corresponding to Mates with ID numbers 01 through 08. Since, as described above, the preferred number of Mates associated with each Mix is eight, the Mix of FIG. 4 is illustrated as being interfaced with eight SCM's 68. The SCM's 68 are similar to the SCM 51 of FIG. 1 in that they strip off the baseband information and demodulate the received audio/video/data and, for transmission, modulate audio/video/data and sum this with baseband information.

Each of the SCM's 68 provides a data output and a data input, a video output and a video input, an audio output and an audio input and a baseband bidirectional input. The audio inputs and outputs of the SCM's 68 are connected to the inputs of an audio switch/summer 70. The audio switch/summer 70 receives eight inputs and provides eight outputs, all of which can be selectively summed with each other. The video outputs and inputs of the SCM 68 are interfaced with a video switch 72 which is controlled to selectively switch video between the SCM's 68. However, the video switch 72 does not sum the videos such that only one of the video inputs to the video switch 72 can be connected to any one of the video outputs at any given time. However, one video input can be connected to all eight outputs. As a practical consideration, video would only be output to a maximum of seven outputs since the originator of the video would not require its video to be fed back.

The Mix 66 has a bidirectional serial data port and an auxiliary serial receiver/transmitter circuit 74 (AUX) for receiving and transmitting the serial data. This is utilized to interface with a serial format such as RS-232 in processing data. In addition, a local area network (LAN) data interface circuit 76 is provided for receiving baseband data from and transmitting data to a LAN network. The received baseband data is processed by the LAN circuit 76 and placed in a format for internal use by the Mix 66 whereas data transmitted from the LAN data interface 76 is converted to baseband data. Although the LAN data interface 76 is illustrated as being connected to a baseband LAN, it should be understood that any type of LAN format can be accommodated. The LAN circuit 76 is utilized only to provide a data interface between a central processing unit and the Mix for control data. Therefore, the LAN circuit 76 forms a ninth port. However, this ninth port is only a data port and does not have video or audio associated therewith. From the standpoint of data communications, the LAN circuit 76 operates similar to the SCM 68 in that it terminates one of the ports of the Mix 66 and allows data communication between two of the devices.

Each of the SCM's 68 have a baseband port connected to a common node 77. This common node 77 interconnects all the baseband ports such that baseband data transmitted on one SCM cable 16 is interfaced with all of the other baseband information on the other SCM cables. As described above, the baseband data transmitted on any of the SCM cables 16 does not carry control data for the Mix or for the video conferencing network. Rather, the baseband link provided through the SCM cable 16 merely facilitates integration of the video conferencing system with an already existing baseband system. However, this is to be distinguished from the baseband interface provided by the LAN circuit 76. This is a dedicated data path for control data generated for the video conferencing system only.

A CPU 78 is provided for controlling the operation of the Mix 66. Both the switching and summing operations in the audio switch/summer 70 and the switching operation of the video switch 72 are controlled by the CPU 78. In addition, the CPU 78
interfaces with data from the auxiliary serial circuit 74 and the LAN interface circuit 76. To provide data for the serial data path to the Mate 10, a serial receiver/transmitter 80 is provided which is connected to the data inputs and outputs of the SCMs 68. Memory 82 is provided for interfacing with the CPU 78 to provide a storage base for the operational software of the Mix 66.

First Level Network Data Flow

In operation of the system shown in FIG. 4a, each of the Mates 10 that are attached to Mix 66 have a direct serial data path with the Mix 66. The Mix 66 provides two functions. First, it operates as a switch to control both the audio switch 70
and the video switch 72 to provide an audio and video path for conferencing between Mate 10 in the system. Secondly, it provides control for the conferencing network to store the status of all of the Mate 10 in the system and also the status of all conferences. To maintain this status, the Mix 66 continually polls the status of all Mates on its various ports. This provides the Mix 66 with information regarding the ID of the Mate and the port to which it is attached and also the status thereof, such as "busy", etc. There is no data path between two Mates in the system but, rather, all data flow must go directly to the Mix and be processed thereby. For example, if the Mate 10 is placing a call, it must request the Mix 66 to check the lines to determine if there is a path available and also to determine if the destination Mate is available. If available, the Mix 66 then sends a message out to the destination Mate to initiate the generation of an audio and video path between the two Mates. Even during a conference, the Mix 66 continually polls the Mates in the conference to determine their status with no data flow occurring between any of the Mates.

Referring now to FIG. 4b, there is illustrated a diagram for the transmission path of both the audio/video/data information for the video conferencing mode and also baseband data for communication between the local processor baseband output and the separate Local Area Network (LAN) through the SCM cable 16, wherein like numerals refer to like parts in the various Figures. The SCM 51 in the Mate 10 is illustrated as having two video information lines 61, one for inputting video into the SCM 51
and one for receiving video from the SCM 51. Two audio input lines 63 are illustrated for inputting audio into the SCM 51 and receiving audio therefrom. Two serial data lines 65 are illustrated for inputting serial data into the SCM 51 and receiving data therefrom. In addition, a baseband input 67 is illustrated that is received from the local processor 42. As described above with reference to FIG. 1, this input is received from the local processor 42 on the line 47 and this would normally constitute a direct interface between the local processor 42 and a separate LAN in the absence of any video conferencing network.

The SCM 51 is connected to the SCM 68 in the Mix 66 through the SCM cable 16. The SCMs 51 and 68 provide three separate and distinct paths for data transmission. A first path 69 is provided for transmission of audio, video and data from the Mate 10 to the Mix 66 for video conferencing purposes. A data transmission path 71 is provided for transmission of audio, video and data from the Mix 66 to the Mate 10, also for video conferencing purposes. A third separate and distinct path 73 is provided for transmission of baseband data that is expressly for the purpose of interfacing with the separate LAN operating at baseband. There is no cross coupling between the data transmitted over the path 73 which is a baseband data path or the audio/video/data information on the paths 69 and 71. In a similar manner, the paths 69 and 71 are also isolated from each other. This isolation between lines 69 and 71 provides the full duplex operation of the video conferencing network of the present invention.

The SCM 68 in the Mix 66 has two lines 75 that are input to the video switch 72, one for outputting video information from the SCM 68 and one for inputting video information thereto. Two lines 79 are provided for interfacing with the audio switch 70, one for receiving audio information from the SCM 68 and one for inputting audio information thereto. Two data lines 81 are provided for interfacing with the serial receiver/transmitter 80, one for receiving data from the SCM 68 and one for transmitting data thereto. The lines 75, 79 and 81 are all internal to the Mix 66 and interface with the various internal components thereof. However, the SCM 68 also filters off the baseband information that was contained on the data path 73 and outputs it on the line 77 to the separate LAN. Therefore, the Mix of FIG. 4a with eight SCMs 68 would have eight lines 77 coming from the Mix 66 to the separate LAN. The SCM cable 16 merely provides a shared data path up to the Mix 66. However, at the Mix 66, the baseband information to the LAN is filtered off and output to a separate cable for connection to the LAN. When interconnecting a number of cables, it is necessary to provide impedance matching and isolation thereto. Therefore, all of the local processors 42 interfaced with the various Mates 10 can utilize the SCM cable 16 to transmit baseband information to the LAN and carry on data communications apart from the video conferencing network. It is important to note that the operation of this LAN is separate and distinct from the video conferencing network and the data transmitted over the path 73 is utilized as a data path from the LAN to the local processor and not to the Mix 66. The LAN interface from the LAN to the video conferencing network must occur through the LAN data interface 76, as will be described hereinbelow with reference to control of the Mix 66 by a centrally located processor on a LAN.

Referring now to FIG. 5, there is illustrated a graph of the frequency spectrum allocation for the SCM cable 16. The lower portion of the spectrum is denoted by reference numeral 84 and is allocated to transmission of the baseband data and is primarily dedicated to use by the local area network apart from the video conferencing network. The audio/video/data for the video conferencing network occupies two portions of the spectrum, a portion 86 and a portion 88. The spectrum portions 86 and
88 are wideband FM modulated signals with the portion 86 centered around 70 Hz and the portion 88 centered around 170 Hz. The audio/video/data information contained in the spectral portion 86 is utilized for transmission in only one direction on the SCM cable 16 and the audio/video/data information contained in the spectral section 88 is utilized for transmission in the opposite direction on the SCM cable 16.

In this manner, frequency division multiplexing is utilized to provide two distinct data paths in a single cable which are isolated from each other. Therefore, the audio/video/data passing from the Mate to the associated Mix is isolated from the audio/video/data transmitted from the Mate to the Mix. Additionally, as described above, baseband data can be transmitted on the same cable to allow the network to accommodate a separate LAN. The baseband is separated off at the Mate and output to the local processor or other LAN device. It is not necessary for the LAN device at the Mates location to interface with the Mate other than the baseband interconnect.

Single Cable Multiplexer

Referring now to FIG. 6, there is illustrated a block diagram of the single cable multiplexer circuits 68 in the Mix 66 and the single cable multiplexer circuit 51 in the Mate 10. The SCM cable 16, as described above, is a single coaxial cable which is connected to an input jack 90 on either the Mix 66 or the Mate 10. The jack 90 is connected directly to one port of a broadband low-pass filter 92, the other port of which is interfaced with a LAN device. The broadband low-pass filter 92
isolates the wideband frequency modulated signal from the LAN device. The jack 90 is also input to one port of a high-pass filter 94. The other port of the high-pass filter 94 is interfaced with a modulation circuit 96 and a demodulation circuit 98. The modulation circuit 96 receives video, audio and data on separate ports thereof and modulates either a 70 mHz or a 170 mHz carrier frequency with this data. Depending upon whether the SCM circuit is associated with either the Mate or the Mix, the modulated carrier will vary. For example, if the modulated carrier for transmitted data is 70 mHz in the Mix, the transmitted data on the Mate will be at 170 mHz to maintain isolation between the two paths.

The demodulator 98 receives the output of the high-pass filter 94 and demodulates the audio and video data. The demodulator circuit 98 operates at the opposite frequency from the modulator. Therefore, if the modulation circuit 96 is operating at 70 mHz, demodulator circuit 98 is operating at 170 mHz. The demodulator circuit 98 provides a data output, an audio output and a video output on separate lines.

The modulation circuit 96 receives the data and modulates it with a modulator 100 onto a subcarrier of 9.0 mHz and also receives the audio and modulates it onto a subcarrier of 10.7 mHz with a modulator 102. The modulated subcarriers output by the modulators 100 and 102 and the video are then summed and input to a 70/170 mHz wideband FM modulator 104. The output of the modulator 104 is input to a 70/170 mHz bandpass filter 106 which has a bandwidth sufficient to pass the spectral information that is output by the modulator 104. This information is passed through the high-pass filter 94 to the jack 90 for input to the SCM cable 16.

The demodulation circuit 98 processes the output of a high-pass filter 94 through a bandpass filter 108 to reject the spectral output of the modulation circuit 96. The bandpass filter 108 is centered around either 170 Hz or 70 mHz, the opposite frequency from that of the modulation circuit 96. The output of the bandpass filter 108 is input to a 170/70 mHz wideband FM demodulator 110 which provides demodulated video and the two modulated subcarriers for audio and data. The output of the demodulator 110 is input to a bandpass filter 112 that is centered about the data subcarrier of 9.0 mHz and then demodulated by a demodulation circuit 114 to output data. A bandpass filter 116 is centered about the audio subcarrier of 10.7 mHz and the signal output therefrom is demodulated by a demodulator circuit 118 to provide the audio output.

The modulators 100 and 102 are FM modulators and are fabricated from devices such as the MC1376 manufactured by Motorola Corp. However, any type of modulator can be utilized. The summing circuit for adding the modulated audio, modulated data and video can be an operational amplifier of the type HA-5195 manufactured by Harris Semiconductors, Inc. The demodulation circuit 110 utilizes phase lock loop technology for wideband FM demodulation. The demodulator 114 for demodulating data is merely a quadrature detector whereas the demodulator 118 for demodulating the audio is of the type MC3356 manufactured by Motorola Corp. Although not shown, an auto symmetry correction circuit is provided for restoring the baseline for the data. A similar type circuit is illustrated in U.S. Pat. No. 4,309,763, issued to Passmore, et. al. on Jan. 5, 1982.

Second Level Video Conferencing Network

Referring now to FIG. 7, there is illustrated a video conferencing network having a plurality of Mix networks contained therein. The network is comprised of a Mix 120 labeled "01", a Mix 122 labeled "02", a Mix 124 labeled "03" and a Mix 126
labeled "04". The labels "01" through "04" are defined as the ID's of the Mixes in the network. It is necessary for each Mix to have an ID to determine priority of network control, as will be described hereinbelow. In the single Mix network described above with reference to FIG. 3 and the First Level Video Conferencing Network, the single Mix controls all network functions, audio/video interconnects, etc. By comparison, the Second Level Network distributes the control in a predetermined manner.

The Mixes 120-126 for simplicity purposes are illustrated as having six ports. The Mix 120 interfaces with the Mix 126 through an SCM cable 128, with the Mix 124 through an SCM cable 130 and with the Mix 122 through an SCM cable 132. The Mix
126 interfaces with the Mix 122 through an SCM cable 134 and with the Mix 124 through an SCM cable 136. The Mix 124 interfaces with the Mix 122 through an SCM cable 138. It is necessary for each Mix to directly interface with every other Mix in the network without having to pass through another Mix. Therefore, depending upon the number of ports in a given Mix, the number of Mixes in a given network is limited since each additional Mix occupies an additional port on every other Mix in the network, thereby reducing the number of remote terminals that can be interfaced with each Mix.

The Mix 120 has a Mate 140 interfaced thereto through an SCM cable 142, a Mate 144 interfaced therewith through an SCM cable 146 and a Mate 148 interfaced therewith through an SCM cable 150. The Mix 122 has a Mate 152 interfaced therewith through an SCM cable 154, a Mate 156 interfaced therewith through an SCM cable 158 and a Mate 160 interfaced therewith through an SCM cable 162. The Mix 126 has a Mate 164 interfaced therewith through an SCM cable 166, a Mate 168 interfaced therewith through an SCM cable 170 and a Mate 172 interfaced therewith through an SCM cable 174. The Mix 124 has a Mate 176 interfaced therewith through an SCM cable 178, a Mate 180 interfaced therewith through an SCM cable 182 and a Mate 184 interfaced therewith through an SCM cable 186.

In operation, each of the Mixes 120-126 has a Master mode and a Slave mode for transferring data through the network. In the Slave mode, the Mix services its own ports to determine the status of all of the devices on each of the ports. This information is maintained in internal tables and defines the status of each of the Mates interfaced therewith and also the status of each of the Mixes interfaced therewith. For example, Mix 122 knows that there are three Mates 152, 156 and 160 attached to specific ports and the ID's of each. In addition, it knows that Mixes 120, 124 and 126 are attached to specific ports and the ID's of each. Mix 122 constantly polls the devices attached to its ports to determine type of device, ID and status.

In the Slave mode, one Mix in the network does not directly interface with a Mate on another Mix in the network. In the Master mode, which operates in conjunction with the Slave mode, the Mix controls the switching operation of all the Mixes in the network, services all of the network requests from the Mate and the other Mixes and also controls multiple Mate video conferences. However, only one Mix in the network can operate in the Master mode. Of the Mixes 120-126 in the network of FIG. 7, only the Mix 120 with the ID "01" is allowed to operate in the Master mode. This is a predefined priority wherein the Mix with the lowest ID in the network operates in the Master mode. If the Mix 120 were turned off and removed from the network, the Mix 122 with the ID "02" would then be reconfigured in the Master mode. In this situation, the network would have to "reconfigure" to update the internal tables in the Master Mode of the Mix 122. The Mix that is operating in the Master mode is termed the "Network Master".

To process a simple call in the network, one of the Mates, for example Mate 140, places a request to call on the 9600 baud serial data path to the Network Master which, in this configuration, resides in Mix 120. The Network Master then looks up in its table to determine both if there is a path available and the shortest path to the destination Mate. It then determines if the destination Mate is busy and, if not, it sends an incoming call message to the destination Mate to place the call. Once the call is placed, the Network Master then reconfigures its internal tables to reflect the new communication path. Additionally, the Network Master can also determine if a previous path has been abandoned and possibly reconnect an ongoing call to this abandoned path if it is a shorter path. Since the transmissions through the network are analog, it is necessary to minimize the signal to noise ratio, thereby requiring the shortest path for communication.

The Mixes 120-126, when operated in the Slave mode, periodically check on the status of all of the ports with "keep alive" messages. In this manner, the status of all the devices can be maintained in an internal table. If the status changes by either adding a call or deleting a call, the Mix in the Slave mode denotes this and sends out a Reconfigure message to the Network Master. The Network Master then acknowledges and the reconfiguration information is then passed from the Slave to the Network Master to maintain an updated table in the Master. Each Mix in the network knows which port the Network Master is connected to since the lowest ID constitutes the Network Master. When the Network Master is removed from the network, it is then necessary for a new Network Master to take over and update its table. This would be the next lowest ID of the Mixes 120-126 remaining in the network.

Second Level Network Data Flow

Referring further to FIG. 7, messages are transmitted on the serial data path from the Mate to either its associated Mix in the Slave mode or to the Network Master, from a Slave Mix to either the Network Master or one of its associated Mates or from the Network Master to any of the Slave Mixes or to any of the Mates. A Mate cannot send data to another Mate or Slave Mix other than its associated Slave Mix nor can a Slave Mix send data to a Mate attached to another Slave Mix. However, a Slave Mix can send a message to the other Slave Mixes for status information. When placing a message onto the serial data path, the originating device encodes this message with information regarding the ID of the originating Mate and also the ID of the destination Mate. For example, if Mate 152 sends a System message out to the Network Master, it encodes its unique ID as the originating device and the ID of the Network Master as the destination device. The Network Master has an ID that is defined as "00". This message is transmitted to the Mix 122 which is operating in the Slave mode. The Mix 122 recognizes the signal as being directed toward the Network Master, which in this example is Mix 120. This message is not processed by the Mix 120 in the Slave mode but, rather, routed through the SCM cable 132 to the mix 120. Mix 120 recognizes the signal as being directed toward the Network Master and also recognizes that the Network Master resides internal thereto. The message is then processed by Mix 120 in the Master mode.

After receiving the message from Mix 152, Mix 120 in the Master mode transmits a response back to Mix 152. This message is also encoded with the ID "00" as the originating device and the ID of the Mate 152 as the destination device. Mix 120
first recognizes that the destination Mate is not attached to any of the ports but recognizes that it is directed toward a Mate on one of the ports of Mix 122. The data is then transmitted back along the SCM cable 132 to the Mix 122. The Mix 122
recognizes this message as being directed toward the Mate 152 rather than to itself and routes the data thereto. Therefore, the Mixes in the Slave mode do not process data from the Network Master prior to routing it to the destination Mate but, rather, access the data, examine the data and then reroute the data.

In another example, the Mix 122 can directly communicate with the Network Master residing in the Mix 120. In this example, the Mix 122 generates a message having its ID as the originating device and the Network Master ID as the destination device. The message is then transmitted from the Mix 122 to the Mix 120, recognized by the Mix 120 as being for the Network Master and allowing the internal network master to process the data. As will be described hereinbelow, the Network Master comprises a virtual tenth port internal to the Mix in which it is residing. Therefore, the data is accessed by the associated Mix and then routed to this virtual tenth port.

Third Level Video Conferencing Network-LAN Based Central

Referring now to FIG. 8, there is illustrated an alternate interconnection between single Mix networks using a broadband interconnect system. The network is fabricated from a plurality of Mix networks of which three are illustrated. A Mix 188
is labeled with the ID "01", a Mix 190 is labeled with the ID "02" and a Mix 192 is labeled with the ID "XX". The Mix 188 has four Mates 194 associated therewith, the Mix 190 has four Mates 196 associated therewith and the Mix 192 has four Mates 198
associated therewith. There can be a plurality of Mix networks with associated Mates in the illustrated network, each having a specific ID.

The Mix 188 is interfaced with a local area network (LAN) 200 through a LAN interface circuit 202 to allow data transfer therebetween. In a similar manner, the Mix networks 190 and 192 are interfaced with the LAN 200 through LAN interfaces 204
and 206, respectively. The LAN interfaces 202-206 are, in the preferred embodiment, integrated into the Mix, as described above with reference to the LAN interface 76 of FIG. 4. They allow the onboard CPU in the Mix to communicate with the LAN. Interfaced with the LAN 200 is a central processing unit 208, hereinafter referred to as the "Central". Whenever the Central 208 is operable, each Mix in the network recognizes the Central 208 as the Network Master regardless of the ID's of the Mixes. Therefore, each of the Mixes in the video conferencing network of FIG. 8 is provided with a direct data interface to the network Master. However, if the Central 208 is removed, each of the Mixes operates independent of the remaining Mixes in the broadband configuration of FIG. 8. It is important to note that the LAN 200 is operable to carry control data at baseband between Mixes in the Network since it is interfacing directly to the internal CPU of each Mix through the interface circuits
202-206. This is to be distinguished from the baseband data transmitted on the SCM cables between Mates and the associated Mix. For example, baseband data transmitted directly from the location of one of the Mates 194 does not get transmitted to the LAN 200. The LAN 200 is only for network data in the configuration of FIG. 8.

The Mix 188 is interfaced with a broadband cable network 210 through an audio and video modulator/demodulator (modem) 212 which is interconnected with one of the ports thereof. In a similar manner, Mix 190 and Mix 192 are also interfaced with the broadband network 210 through audio/video modems 214 and 216, respectively. The broadband network is a network such as a CATV system which provides a plurality of discrete channels which are selectable by the audio/video modems 212-216. Selective switching of channels with the modems 212-216 enables a data link to be formed between any two of the Mixes 188-192. Once a channel in the broadband cable network 210 is selected by the modems associated with Mixes in a video conference network, the data link appears no different than the SCM cable link in the network configuration of FIG. 3. There is still a direct audio/video/data path between interconnected Mixes for a two way conference. However, the use of the LAN for communication between the Network Master and associated Mixes in the Slave mode eliminates the need for transmitting data over the broadband network 210.

When the system of FIG. 8 is utilized for multiway conferences, the Network Master