HlllllllllllllllIllll||||lIllll|||l|IlllilllllIllllllilllllllllillllllllll
`U3005561670A
`
`United States Patent
`
`[19]
`
`[11] Patent Number:
`
`5,561,670
`
`Hoffert et al.
`[45] Date of Patent: Oct. 1, 1996
`
`
`
`[54]
`
`[75]
`
`[73]
`
`METHOD AND APPARATUS FOR
`OPERATING A MULTICAST SYSTEM ON AN
`UNRELIABLE NETWORK
`
`Inventors: Eric M. Hofl’ert, San Francisco; Mark
`A. Green, Albany, both of Calif.
`
`Assignee: Apple Computer, Inc., Cupertino,
`Calif.
`
`[21]
`
`Appl. No.: 242,138
`
`[22]
`
`Filed:
`
`May 13, 1994
`
`[51]
`
`[52]
`
`[58]
`
`[56]
`
`Int. Cl.6 .............................. H04J 3/12; H04L 12/56;
`H04N 7/08
`
`US. Cl. .......................... 370/94.1; 370/1101; 348/6;
`348/467; 348/474
`Field of Search 1-......................... 370/60, 60.1, 94.1,
`370/942, 94.3, 110.1, 119; 348/6, 10, 429,
`460, 461, 462, 473, 474, 522, 555, 467;
`380/10, 20; 340/8253
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4,866,770
`4,890,321
`4,905,282
`4,953,210
`5,150,113
`5,200,952
`5,289,276
`
`...................... 380/20
`348/6 X
`
`9/1989 Seth-Smith et a1.
`12/1989 Seth-Smith et al.
`...... 380/48
`......
`2/1990 McGlynn et al.
`...... 380/48
`..
`8/1990 McGlynn et al.
`
`9/1992 Bliithgen .............
`. 340/8253
`
`...... 370/79
`4/1993 Bernstein et al.
`..
`........................ 348/467
`2/1994 Siracusa et al.
`
`FOREIGN PATENT DOCUMENTS
`
`.
`0405954 12/1990 European Pat. Off.
`0579075
`1/1994 European Pat. OE. .
`OTHER PUBLICATIONS
`
`Hayden, Peter C., “LAN Addressing for Digital Video
`Data”, Digital Technical Journal, vol. 5, No. 2, Spring 1993,
`pp. 77—83.
`Jiang and Hopper, “Architectural Support for Multipoint
`Digital Video Communications”, IEEE, Feb. 1993, pp.
`1358—1362.
`Strigini, Fratta and Albanese, “Multicast Services on High-
`—Speed’1nterconnected LAN”, IFIP, 1987, pp. 173—177.
`LaPorta and Schwartz, “The Multistream Protocol: A Highly
`Flexible High—Speed Transport Protocol”, IEEE, vol. 11,
`No. 4, May 1993, pp. 519—530.
`Primary Examiner—Hassan Kizou
`Attorney, Agent, or Firm—Carr, DeFilippo & Ferrell
`[57]
`ABSTRACT
`
`A multicast network system comprises a data network which
`provides a medium for data transfer. A media source having
`a control packet and media packets coupled to the data
`network broadcasts the control packet and the media packets
`to the data network and rebroadcasts the control packet in
`conjunction with the media packets to the data network. A
`media receiver is coupled to the network and receives the
`control packet and the media packets from the data network
`to process the control packet and the media packets to
`produce a media output.
`
`15 Claims, 6 Drawing Sheets
`
`20
`
`34
`
`20
`
`34
`
`20
`
`-
`
`.
`
`- @AVDATA @AVDATA
`
`.
`
`-
`
`'30
`
`‘___________________f
`T T TIME T
`1
`
`.32
`
`".32
`
`Apple Exhibit 4421
`
`Apple v. SightSound Technologies
`CBM2013-00023
`
`Page 00001
`
`Apple Exhibit 4421
`Apple v. SightSound Technologies
`CBM2013-00023
`Page 00001
`
`

`

`US. Patent
`
`Oct. 1, 1996
`
`Sheet 1 of 6
`
`5,561,670
`
`FI.1
`
`Page 00002
`
`Page 00002
`
`

`

`US. Patent
`
`Oct. 1, 1996
`
`Sheet 2 of 6
`
`5,561,670
`
`270
`
`
`
`NUMBER
`
`I
`TYPE
`_______l__..__._.____
`l
`_______l_____._...._
`l
`
`§I€5_W_’Q_l ________
`________l.._______
`l
`
`
`
`
`
`
`220
`
`2.30
`
`240
`
`,
`
`250
`
`
`
`
`
`
`
`
`5TR54M TYPE
`
`STREAM ID
`
`TIME SCALE
`
`PRIOR/TY
`
`UNIQUE
`STREAM INF0
`
`&0
`
`FIG. 28
`
`Page.00003
`
`Page 00003
`
`

`

`US. Patent
`
`Oct. 1, 1996
`
`Sheet 3 of 6
`
`5,561,670
`
`20
`
`34
`
`‘20
`
`34
`
`20
`
`T/ME T
`
`M
`
`52
`
`M
`
`\
`
`J2
`
`FVCi
`
`:3
`
`4.9
`47
`r—’ “fir—A—‘fi
`
`420
`
`420
`
`420
`
`420
`
`420
`
`fWM3.-4/4
`
`TIME STAMP
`
`PRIOR/W
`
`SEQUENCE NUMBER
`
`SIZE
`
`fWM3.-4£3
`
`
`
`
`
`
`450
`
` 440
`
`
`
`460
`
`470
`
`ng
`
`55
`
`58
`
`56
`
`54
`
`52
`
`54
`
`52
`
`E_____________4_0
`
`K——wr-J
`
`WME
`
`“2
`53
`
`”x
`
`0
`FVEi
`
`57
`:5
`
`”2
`53
`
`Page 00004 *
`
`Page 00004
`
`

`

`US. Patent
`
`Oct. 1, 1996
`
`Sheet 4 of 6
`
`5,561,670
`
`
`
`670
`
`INITIAL/2E MESSAGE ARRAY
`
`AND INDEX r0 ZERO
`
`
`
`6.30
` INITIAL OR
`NEW SE7: OF
`
`FORMAT
`
`
`INFORMATION
`
`650
`
`
`
`SET TIME = CURRENT TIME
`SET INDEX = 0. FLUSH ARRAY
`
`CREATE NEW MESSAGE ARRAY'
`
`
` COMPARE
`TIME T WITH
`
`
`IF > M BROADCAST
`
`
`CONTROL
`
`TIME C
`
`PACKET
`
`6‘80
`
`CONNECT/ON
`
`T0 NETWORK
`
`”0-
`
`685
`
`
`
`
`
`
`
`TRANSM/T OPEN CHANNEL
`MESSAGE AND N OPEN
`
`690
`
`STREAM MESSAGES.
`SEr TIME T = G
`
`
`FIG. 6'
`
`Page 00005
`
`Page 00005
`
`

`

`US. Patent
`
`Oct. 1, 1996
`
`Sheet 5 of 6
`
`5,561,670
`
`
`INITIALIZE MESSAGE ARRAY
`
`AND INDEX TO ZERO
`
`
`
`
`
`
`CONNECT/ON
`T0 NETWORK
`
`
`
` EXAM/NE ,
`
`PACKET HEADER
`FOR CONTROL
`
`PACKET
`
`
`
`
`
`COMPARE
`
`INCOMING
`
`
`MESSAGE WITH
`
`MESSAGES IN
`
`MESSAGE
`
`ARRAY
`
`
`
`
`SET MESSAGE INDEX = 0
`FLUSH MESSAGE ARRAY
`
`COPY MESSAGE TO ARRAY
`
`INCREMENT INDEX
`
`
`
`
`
`
`
`
`'
`IF N
`COMPARE
`OPEN STREAM
`
`
`
`STREAM IDS
`MESSAGES
`N0
`
`WITH MESSAGE
`
`ARRAY
`
`760
`
`
`COPY OPEN
`
`STREAM MESSAGE
`PROCESS
`
`
`IN ARRAY
`MED/A DA TA FIG. 7
`
`
`
`Page 00006
`
`Page 00006
`
`

`

`US. Patent
`
`Oct. 1, 1996
`
`Sheet 6 of 6
`
`5,561,670
`
`00
`09
`
`FIG.8
`
`Page 00007
`
`Page 00007
`
`

`

`5,561,670
`
`1
`METHOD AND APPARATUS FOR
`OPERATING A MULTICAST SYSTEM ON AN
`UNRELIABLE NETWORK
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`This invention relates to data transfers between devices on
`
`a high speed digital network, and more particularly to a
`system and method for receiving an audio/visual multicast
`source on a high speed local or wide area packet network.
`2. Description of the Background Art
`In recent years, digital video data transmission over a
`local area network (LAN) has become more common.
`Before analog video data is transferred onto the LAN,
`analog video is converted to digital format. Available acces-
`sory hardware and software receive broadcast video pro-
`gramming and convert the analog video into digital format.
`Other hardware and software compress the digital format to
`digital video data that can be efficiently transferred to a
`personal computer or data network. Analog video data
`includes video programming material that is broadcast live,
`current programming broadcast on a television network, or
`pre-recorded programming. Often times, many devices
`monitor the transmission of the video programming that is
`broadcast onto the LAN.
`
`In order to transmit digital video data over a data network,
`an efiective transfer scheme for sending and retrieving the
`video data is required for the data network. Most data
`networks support three basic transfer schemes: a unicast
`addressing scheme where data is sent to one unique device
`on the data network, a broadcast addressing scheme where
`data is sent to all devices on the data network, and a
`multicast addressing scheme where data is sent to a group of
`devices on the data network. Each type of addressing
`scheme has characteristics that are both desirable and unde-
`sirable.
`
`The unicast addressing scheme works well in a network
`system where only one output device receives the digital
`data from the data network. If there is a requirement that
`multiple output devices receive the digital data, then the
`source device has to retransmit the digital data for each
`additional output device. As the number of additional output
`devices increases, the data network quickly becomes over-
`loaded and congested.
`The broadcast addressing scheme permits multiple output
`devices to receive the digital data without requiring the
`source device to transmit multiple sets of digital data.
`However, the broadcast digital data is also transmitted to
`devices that are not interested in the digital data These
`devices have to receive the digital data and reject it. Thus,
`the broadcast of digital data onto the data network affects
`other devices on the data network. The problem is com—
`pounded when routers or network bridges are required to
`broadcast the digital data needlessly to neighboring data
`networks.
`
`The multicast addressing scheme enables the transmission
`of digital data to be received by a select group of output
`devices on the data network system. Digital data is only
`received by the output devices that are interested in receiv—
`ing the digital data. Available network adapters provide high
`speed filtering of multicast addresses for high performance
`rejection/selection of multicast addresses. Thus, a multicast
`addressing scheme is suitable for the selective transmission
`of digital data. However, the multicast addressing scheme
`
`10
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`15
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`2
`
`has drawbacks when the scheme is used to transmit digital
`video programming.
`Audio and video digital data converted for transfer on the
`data network include descriptive control information that
`has to be received by the receiving output device before the
`digital video data can be processed for output. In a unicast
`addressing scheme,
`the receiving output device
`can
`acknowledge the receipt of the descriptive control inforrna—
`tion before the source device proceeds to transmit the digital
`video data. In a multicast addressing scheme on an unreli-
`able or lossy network, the source device does not receive
`acknowledgment signals from receiving output devices. The
`source device transmits digital video data onto the data
`network without regard to whether receiving output devices
`can receive and process the digital video data. Therefore, it
`is desirable to design a data network for receiving digital
`video data from a multicast addressing scheme that provides
`efiicient transfer of digital video data which improves and
`overcomes the disadvantages of the prior art. The improved
`multicast addressing scheme should permit
`receiving
`devices to tap into and receive the multicast digital video
`data on the data network.
`
`SUMMARY OF THE INVENTION
`
`In accordance with the present invention, a multicast
`network system comprises a data network which provides a
`medium for data transfer. A media source having a control
`packet and media packets coupled to the data network,
`broadcasts the control packet and the media packets to the
`data network and rebroadcasts the control packet in con—
`junction with the media packets to the data network. A media
`receiver is coupled to the network and receives the control
`packet and the media packets from the data network to
`process the control packet and the media packets to produce
`a media output. The media receiver filters rebroadcasts of
`the control packet after successful processing of the control
`packet. The control packet
`includes format
`information
`pertaining to the media packets so that the media packets can
`be processed by the media receiver to produce the media
`output. The media packets include audio information and
`video information which are processed by the media
`receiver to produce the media output. The control packet is
`rebroadcast at a fixed time interval from a previous broad-
`cast of the control packet.
`A media receiver can tap onto the data network and begin
`receiving the media information. By rebroadcasting the
`control packet onto the data network, a media receiver can
`retrieve the control packet and obtain the format informa—
`tion. Once the format information is received, the media
`receiver can begin processing the media packets. The media
`packets can be stored for later output or be used to provide
`the media output. The control packets are typically on the
`order of 500 to 2000 bytes/sec while the media packets are
`typically on the order of 100 to 200 Kbytes/sec. The ratio of
`control packets to media data is approximately 100 to 1.
`Thus, rebroadcasting the control packet onto the data net-
`work does not impact the throughput rate of the media
`packets. Additional media receivers can tap into the network
`and be assured of promptly receiving the important format
`information.
`
`According to another aspect of the invention, the media
`source broadcasts a second control packet which changes
`format information pertaining to the media packets broad-
`cast by the media source. The media receiver completes
`processing of the second control packet before processing
`
`Page 00008
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`Page 00008
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`

`

`5,561,670
`
`3
`the media packets from the data network. As the format
`information of the media packets changes, the second con-
`trol packet corresponding to the new format information is
`broadcast onto the data network.
`
`A second media receiver in another aspect of the inven—
`tion is coupled to the data network which processes the
`control packet and the media packets broadcast by the media
`source to produce a second media output. The second media
`receiver completes processing of the control packet before
`processing the media packets from the data network.
`Rebroadcasting of the control packets permits additional
`media receivers to tap onto or “tune in” to the data network
`and retrieve the format information from the control packets.
`Once the format information is retrieved, any additional
`media receiver can begin processing the media packets.
`The present invention can also be characterized as a
`method of operating a multicast network comprising the
`steps of generating a control packet which includes format
`information,
`transferring media packets which include
`media information, broadcasting the control packet and the
`media packets to the multicast network, and rebroadcasting
`the control packet in conjunction with the media packets.
`The method further comprises the step of broadcasting the
`control packet and the media packets on an unreliable
`network. The method further comprises the step of receiving
`the control packet and the media packets, and processing the
`control packet and the media packets to produce a media
`output.
`The format information pertains to the media packets and
`the method further comprises the step of processing the
`format information before processing the media packets.
`The method further comprises the step of ignoring the media
`packets until
`the format
`information is processed. The
`format information includes open channel information and
`open stream information and the method further comprises
`the step of generating an array of the open channel infor-
`mation and the open stream information.
`
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`packets on the network. The receiver completes processing
`the control packet to obtain the description data pertaining to
`the media packets so that the data processor can process the
`media packets to produce the media output. The receiver
`receives rebroadcasts of a second control packet having
`second data format
`information for storage to the data
`format memory. The receiver ignores processing of the
`media packets until the second data format information is
`stored in the data format memory.
`Other aspects and advantages of the present invention can
`be seen upon review of the Figures, the Detailed Description
`and the Claims which follow.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 depicts a multicast network system of the present
`invention;
`FIG. 2a depicts an exemplary block diagram of a control
`packet of the present invention having format information;
`FIG. 2b depicts an exemplary block diagram of a message
`array for storing control packet information;
`FIG. 3 is a time line depicting media information trans-
`ferred on the multicast network system;
`FIG. 4a is an exemplary block diagram of a section of AV
`data that is transferred on the multicast network system;
`FIG. 4b is an exemplary block diagram of the format
`information that is included in a datagram;
`FIG. 5 is a time line depicting media information corre»
`sponding to a new control packet transferred on the multi-
`cast network system;
`FIG. 6 is a flow diagram of a media source providing a
`control packet to the multicast network system;
`FIG. 7 is a flow diagram of a receiving device receiving
`format information from a control packet on the multicast
`network system; and
`FIG. 8 depicts an embodiment of the present invention in
`an expanded multicast network system.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`
`FIG. 1 is an embodiment of the present invention depict-
`ing a multicast network system 10. A multicast network
`system 10 provides continuous broadcasts of media infor-
`mation on network 5. Network 5 can be a conventional
`
`AppleTalk, TCP/IP, ATM, IPX, or other similar network. A
`media source 2 is coupled to the network 5 and provides the
`continuous broadcasts of media information. The media
`information includes multimedia information from a cam-
`corder, laser disc player, or other audio/video device. The
`media source 2 provides simultaneous or recorded broad-
`casts of media information onto network 5. Receiving audio
`device 4 is coupled to the network 5 and taps audio infor-
`mation from the network 5. Receiving audio device 4 can be
`a conventional desktop computer or portable computer that
`is configured to receive audio information. Receiving audio
`device 4 processes the audio information to provide an audio
`output at audio device 4. The receiving audio device 4 can
`store the audio information for playback at a later time.
`Receiving video device 6 is coupled to the network 5 and
`taps video information from the network 5. Receiving video
`device 6 can be another conventional desktop computer or
`portable computer that is configured to receive video infor—
`mation. Receiving video device 6 processes the video infor-
`mation to provide a video output at video device 6. The
`receiving video device 6 can store the video information for
`
`Page 00009
`
`According to another aspect of the invention, the step of p
`processing the format
`information includes the step of
`receiving the open channel information and the open stream
`information from the multicast network, and building the
`array of the open channel information and the open stream
`information. The method further comprises the step of
`generating a second control packet which includes second
`format information, transferring media packets which con-
`form to the second format information, broadcasting the
`second control packet and the media packets to the multicast
`network, and rebroadcasting the second control packet in
`conjunction with the media packets. The method further
`comprises the step of receiving the second control packet
`and the media packets, and processing the second control
`packet and the media packets to produce a second media
`output.
`The present invention can further be characterized as a
`media device coupled to a network comprising a receiver
`having a data format memory which receives rebroadcasts of
`a control packet having data format information for storage
`to the data format memory. A data processor coupled to the
`receiver receives the data format information so that media
`packets having media information can be processed by the
`data processor. An output coupled to the data processor
`receives the media information from the data processor to
`provide a media output. The media device further comprises
`a storage device which stores the media information from
`the data processor for media output at a later time.
`According to another aspect of the invention, the control
`packet includes description data pertaining to the media
`
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`

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`5
`
`6
`
`5,561,670
`
`playback at a later time. Receiving audio/video device 8 is
`also coupled to the network 5 and taps audio and video
`information from the network 5. Receiving audio/video
`device 8 can be a multimedia computer or portable multi-
`media computer (also referred to as a “data processor”) that
`is configured to receive audio and video information.
`Receiving audio/video device 8 processes the audio and
`video information to provide an audio and video output at
`audio/video device 8. The receiving audio/video device 8
`can store the audio and video information for playback at a
`later time. Receiving devices 4, 6 and 8 are referred to
`collectively as receivers.
`In order to maintain high speed transmissions, network 5
`is an unreliable network. A receiving device coupled to the
`network 5 does not send an acknowledgment of receipt
`when the receiving device successfully receives transmitted
`data. Media source 2 broadcasts media information onto
`network 5 without receiving an acknowledgment of receipt
`from a receiving device. If a receiving device requires access
`to the media information, the receiving device can tap into
`or “tune in” to network 5 during the transmission of media
`source 2. For example, receiving audio/video device 8 can
`tap into network 5 and begin receiving media information
`from the network 5. The receiving audio/video device 8
`receives the media information and processes the media
`information for output. Other receiving audio devices 4,
`video devices 6 or audio/video devices 8 can tap into the
`network 5 and begin receiving and processing the media
`information for output or storage.
`Segments of digital data transferred using an unreliable
`network are often lost during transmission. When transfer-
`ring media information, certain segments of the media
`information are imperative to the transmission and cannot be
`lost. The media information that is transferred on the net-
`work 5 includes audio/video data. The audio data is trans-
`
`ferred in packets of audio samples and the video data is
`transferred in packets of video frames. Media source 2
`transfers the packets of video frames and audio samples onto
`the network 5 in data streams. Before the data streams of
`video frames and audio samples can be received, a control
`packet having format information pertaining to the video
`frames and the audio samples has to be received. If the data
`includes audio frames, the format information comprises
`compression, sampling rate, bits per sample, stereo/mono,
`and other data pertaining to the audio frames. If the data
`includes video frames, the format information comprises
`compression, spatial resolution, pixel depth, quality level
`and other data pertaining to the video frames. To ensure that
`the control packet is received by a receiving audio device 4,
`video device 6, or audio/video device 8, the control packet
`is rebroadcast onto the network at certain predetermined
`time intervals. Rebroadcasting also ensures that receiving
`devices 4, 6, and 8 can tap into or “tune in” to the network
`5 and begin processing the media information when the
`transmission of the media information is in progress. The
`media source 2 is also referred to as “means for transmitting
`media and control packet digital signals.” Receiving devices
`4, 6 and 8 each comprise memory, including data format
`memory for storing format information contained in control
`packets and media packet digital signal storage devices for
`storing received media information.
`Referring now to FIG. 2a, a block diagram of a control
`packet 20 having format information is shown. The control
`packet 20 includes an open channel section 210 and an open
`stream section 260. The open channel section 210 includes
`message information about the format of the data streams
`that are currently being broadcast on the network 5. Number
`
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`block 220 of open channel section 210 provides information
`on how many different data streams are to be received from
`the network 5. Type block 230 is an array that provides
`information about the type of each stream. For example, the
`type of the stream may be video or audio. Stream ID block
`240 is an array that provides a stream identifier for each
`stream. The stream identifier is a unique number for iden-
`tifying a particular stream.
`The open stream section 260 provides information about
`a particular stream in the data stream. Stream type block 262
`of the open stream section 260 provides information about
`the type of the particular stream. The type of the stream may
`be video or audio. Stream ID block 264 provides the unique
`number identifying the particular stream. Time scale block
`266 provides information about the rate at which the stream
`is being transferred. The time scale block 266 provides the
`number of units per second for the particular stream. Priority
`block 268 provides information about the importance of the
`particular stream as compared to other streams which cor-
`respond to the particular open channel section 210.
`The open stream section 260 of control packet 20 further
`provides a block having unique stream information 269.
`Depending on the particular type of the stream, certain
`unique stream information 269 pertaining to the particular
`stream is provided. If the particular open stream section 260
`describes a video stream message, the unique stream infor-
`mation 269 includes data pertaining to data compression,
`spatial resolution, pixel depth,
`temporal compression or
`quality level of the particular video stream. Receiving
`devices use the unique stream information 269 to process the
`particular stream for output or storage. The unique stream
`information 269 includes additional open stream informa-
`tion that is unique to the particular type of the stream. The
`additional open stream information 269 varies depending on
`the particular type of the stream. For instance, if instead the
`particular open stream describes an audio stream, the unique
`stream information 269 includes data pertaining to data
`compression, sample rate, bits per sample, stereo or mono of
`the particular audio stream. The unique stream information
`269 for the video stream is different compared to the unique
`stream information 269 for the audio stream.
`
`Referring now to FIG. 2b, a message array 200 is gener-
`ated to organize the format information from'the control
`packet 20 of FIG. 2a. Media source 2 generates the message
`array 200. Whenever media source 2 rebroadcasts the con—
`trol packet 20,
`the message array 200 is accessed and
`transferred onto the network 5. Entry 220 in message array
`200 corresponds to number block 220 of the open channel
`section 210. Similarly, entries 230, 240, 262, 264, 266, 268,
`and 269 correspond to type 230, stream ID 240, stream type
`262, stream ID 264, time scale 266, priority 268, and unique
`stream information 269 of the control packet 20 of FIG. 2a.
`The receiving audio device 4, video device 6, and audio/
`video device 8 generate similar message arrays 200 for
`receiving the format information for the control packet 20.
`FIG. 3 is a section of a time line 30 illustrating the
`temporal transmission of media information on the network
`5. Control packet 20 is rebroadcast at each time interval M
`32. Between time intervals M 32, AV data 34 is transferred
`on the network 5. Media source 2 transfers AV data 34 onto
`
`the network 5 for receipt by receiving devices 4, 6, and 8.
`Before a receiving device 4, 6, or 8 receives and processes
`the AV data 34, the receiving device 4, 6, or 8 receives
`format information included in control packet 20. Similarly,
`if a receiving device 4, 6, or 8 taps onto the network 5, the
`receiving device 4, 6, or 8 receives format information
`included in control packet 20 before the receiving device 4,
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`6, or 8 receives and processes the AV data 34. Rebroadcast—
`ing the control packet 20 at time intervals M 32 assures a
`receiving device 4, 6, or 8 receives the control packet 20.
`Once the format information included in the control packet
`20 is received, the receiving device 4, 6, or 8 receives and
`processes the AV data 34 for output or stores the AV data 34
`for later output. The control packets 20 are typically on the
`order of 500 to 2000 bytes/sec while the packets of AV data
`34 are typically on the order of 100 to 200 Kbytes/sec. The
`ratio of control packets 20 to packets of AV data 34 is
`approximately 100 to 1. Thus, rebroadcasting the control
`packet onto the data network does not impact the throughput
`rate of the packets of AV data 34 on network 5.
`FIG. 4a is a block diagram of a section of AV data 34. The
`AV data 34 includes the packets of media information, which
`may be video frames 42 and 44 or audio samples 45, 46, and
`48. Video frame 42 and audio samples 46 and 48 comprise
`a media component 49. Similarly, video frame 44 and audio
`sample 45 comprise a media component 47. Other media
`components 47 and 49 are formed using combinations of
`video frames 42 and 44 and audio samples 45, 46, and 48.
`The audio/video device 8 provides an audio/video output
`when a complete media component 47 or 49 is received and
`processed. Incomplete media components 47 and 49 that are
`received by audio/video device 8 are not processed for
`output or storage. To determine whether a complete media
`component 47 or 49 is received, each video frame 42 and 44
`and audio sample 45, 46, and 48 is preceded by a datagram
`420. Datagrams 420 include format information pertaining
`to the media component 47 or 49 that is transmitted on the
`network 5. Some video frames 42 and 44 have multiple
`datagrams 420. Similarly, audio samples 45, 46, and 48 can
`have multiple datagrarns 420. The number of datagrams 420
`is proportional to the size of the media component 47 or 49.
`Using the datagrams 420, the original media component 47
`or 49 sent by media source 2 can be reconstructed by the
`receiving device 4, 6, or 8.
`FIG. 4b is an exemplary block diagram of the format
`information that is included in a datagram 420. A time stamp
`section 440 provides information pertaining to when the
`corresponding section of a media component 47 or 49 was
`placed on the network 5. When media components 47 and 49
`are stored for later playback, the time stamp section 440
`facilitates synchronized playback of the stored media com-
`ponents 47 and 49. Priority section 450 provides information
`pertaining to the importance of the corresponding section of
`the media component 47 or 49. Depending on the priority of
`a particular media component 47 or 49, some devices
`coupled to the network 5 may not process the particular
`media component 47 or 49. Sequence number 460 provides
`information pertaining to the relative position of a datagram
`420 within a video frame 42 or 44, or audio sample 45, 46,
`or 48. Size section 470 provides information pertaining to
`the size of the corresponding section of the media compo-
`nent 47 or 49. A receiving device 4, 6, or 8 receives
`datagrams 420 from the network 5 and determines whether
`a complete media component 47 or 49 is received. Many
`factors can cause the loss of a section of media component
`47 or 49 by the receiving device 4, 6, or 8. For instance, the
`network 5 may be congested, or the receiving device 4, 6, or
`8 can not process the incoming high bandwidth media
`information from the network 5. When a section of the
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`media component 47 or 49 is lost, the receiving device 4, 6,
`or 8 can determine that the received media component 47 or
`49 is not complete from another received datagram 420. If
`the received media component 47 or 49 is not complete,
`receiving device 4, 6, or 8 does not process the received
`media component 47 or 49 for output or storage.
`
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`FIG. 5 is a section of a time line 50 showing media
`information on the network 5 as format information supplied
`by control packet 52 is changed to new format information
`of control packet 56. Control packet 52 is rebroadcast at the
`end of each time interval M 53. During time intervals M 53,
`AV data 54 is transferred on the network 5. Media source 2
`transfers AV data 54 conforming to format information of
`control packet 52 onto the network 5 for receipt by receiving
`devices 4, 6, and 8. During interval N 57, control packet 52
`is changed to control packet 56. Whenever media source 2
`receives a new control packet 56, the new control packet 56
`is transferred onto the network 5 without delay. The new
`control packet 56 changes the format of the AV data 54 on
`the network 5. In FIG. 5, the new control packet 56 is
`received during time interval N 57 and is transferred onto the
`network 5 after time interval N 57. Following the transfer of
`the new control packet 56, new AV data 58 that is transferred
`onto the network 5 conforms to the format information of
`
`new control packet 56. Subsequent rebroadcasts of new
`control packet 56 revert to the prescribed time intervals M
`53. Over the duration of the transfer of AV data 54 on
`network 5, many new control packets 56 can occur changing
`the format information of the AV data 54 transferred on the
`network 5.
`
`Referring now to FIG. 6, a simplified exemplary flow
`diagram of media source 2 providing a control packet having
`format information onto the network is illustrated. The flow
`
`diagram begins at start step 610. Media source 2 initializes
`the index of the control packet message array 200 to zero,
`and the control packet message array 200 is cleared to
`contain no entries. The control packet message array 200
`includes format information pertaining to the media infor-
`mation that is transferred onto the network 5.
`
`In step 630, if media source 2 receives an initial or new
`set of format information for transfer onto the network 5, the
`control packet message array 200 is initialized or replaced
`with the initial or new set of format information. If an initial
`or new set of format information is not received, the flow
`diagram skips to step 670. Skipping to step 670 occurs when
`the format
`information of control packet 52 re