United States Patent
`Cloutier et al.
`
`[19]
`
`USOO58 47771
`
`A
`Patent Number:
`Date of Patent:
`
`5,847,771
`Dec. 8, 1998
`
`[54] DIGITAL ENTERTAINMENT TERMINAL
`PROVIDING MULTIPLE DIGITAL PICTURES
`
`[75] Inventors: Leo Cloutier, Bethesda, Md.; Paul
`Brewer, Arlington, Va.
`
`[73] Assignee: Bell Atlantic Network Services, Inc.,
`Arlington, Va.
`
`[21] Appl. No.: 698,281
`[22]
`Filed:
`Aug. 14, 1996
`
`[51] Int. Cl.6 ............................ .. H04N 5/445; H04N 5/45
`[52] US. Cl. ........................ .. 348/564; 348/565; 348/567;
`348/568; 348/588
`[58] Field of Search ................................... .. 348/564, 565,
`348/567, 568, 588, 598; 382/240; H04N 5/445,
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5,481,315
`
`1/1996 Matsunaga ............................ .. 348/565
`
`Attorney, Agent, or Firm—McDermott, Will & Emery
`
`[57]
`
`ABSTRACT
`
`TWo MPEG-encoded digital data streams are simultaneously
`decoded in a digital entertainment terminal to provide
`Picture-in-Picture (PIP) and Picture-on-Picture (POP) capa
`bilities for a conventional television. A primary MPEG
`encoded data stream is decoded using a digital video pro
`cessor optimized for MPEG2 decoding or a dedicated
`MPEG2 decoder system. A secondary MPEG-encoded data
`stream is partially processed by ?ltering the B frames of the
`secondary MPEG-encoded data stream and using the corre
`sponding I and P frames in a partial decoding arrangement
`to obtain decompressed video data providing a limited
`resolution representation of a second program. Partial
`decoding may also be performed using only I frames. The
`partial decoding may be implemented through execution of
`softWare by a general-purpose microprocessor.
`Alternatively, the media processor may perform the partial
`decoding during the idle intervals of the dedicated media
`processor.
`
`Primary Examiner—Sherrie Hsia
`
`48 Claims, 8 Drawing Sheets
`
`28
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`|___________________
`
`ASUS Exhibit 1006 - Page 1
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`

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`U.S. Patent
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`Dec. 8, 1998
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`Sheet 1 0f 8
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`5,847,771
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`Figure 1
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`ASUS Exhibit 1006 - Page 2
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`

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`U.S. Patent
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`Dec. s, 1998
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`Sheet 2 of 8
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`5,847,771
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`ASUS Exhibit 1006 - Page 3
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`

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`U.S. Patent
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`Dec. 8, 1998
`
`Sheet 3 of8
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`5,847,771
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`ASUS Exhibit 1006 - Page 4
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`

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`U.S. Patent
`
`Dec. s, 1998
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`Sheet 4 of 8
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`5,847,771
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`ASUS Exhibit 1006 - Page 5
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`

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`U.S. Patent
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`Dec. s, 1998
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`Sheet 5 of8
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`5,847,771
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`Figure 6A
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`ASUS Exhibit 1006 - Page 6
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`

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`U.S. Patent
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`Dec. s, 1998
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`Sheet 6 of 8
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`5,847,771
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`Figure 7
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`
`ASUS Exhibit 1006 - Page 7
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`

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`U.S. Patent
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`Dec. s, 1998
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`Sheet 7 of 8
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`5,847,771
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`Figure 8 f 86
`
`Application
`
`‘/ 88
`
`MPEG 2 Compressed
`Buffer (Main)
`
`Decompressed Main
`Frames
`
`‘/ 90
`
`‘/ 92
`
`PIP MPEG 2 Compressed ./ 94
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`
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`
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`ASUS Exhibit 1006 - Page 8
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`

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`U.S. Patent
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`Dec. s, 1998
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`Sheet 8 of 8
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`5,847,771
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`Figure 10
`
`P1=(X1, Y1)
`K.
`
`202
`/
`
`P3 = (Xb, Yb)
`
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`
`ASUS Exhibit 1006 - Page 9
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`

`
`1
`DIGITAL ENTERTAINMENT TERMINAL
`PROVIDING MULTIPLE DIGITAL PICTURES
`
`TECHNICAL FIELD
`
`The present invention relates to a programmable digital
`entertainment terminal (DET) for use in digital video pro
`gram distribution netWorks and to systems and methods for
`providing picture-in-picture and picture-on-picture capabili
`ties in digital video systems.
`
`BACKGROUND ART
`Conventional televisions may contain special circuitry to
`perform picture-in-picture (PIP), Where tWo programs are
`vieWed simultaneously. A picture-in-picture feature gener
`ally provides a small image of the picture or video portion
`of a secondary program signal inset Within the display of a
`normal primary video program. Picture-on-picture (POP)
`images use similar techniques to provide images that have a
`secondary program signal positioned beside a main picture
`rather than overlying the main picture.
`Implementation of PIP or POP in a digital video netWork
`feature requires processing of tWo digital image signals, one
`for the primary program selection and a second for the
`picture-in-picture inset. In digital video networks, presenta
`tion of selected video programs via an analog television set
`requires a digital decoder, often referred to as a digital
`set-top box or digital entertainment terminal. The digital
`set-top box includes dedicated digital signal processing
`circuitry for decoding the digital video signals from the
`netWork. For example, a set-top box for reception of MPEG
`encoded digital video signals typically includes a digital
`demultiplexer, an MPEG video decoder, an MPEG audio
`decoder and circuits for converting decompressed digital
`video and audio streams from the decoders into analog
`signals for driving a television receiver. Since implementa
`tion of PIP in digital netWorks requires processing of tWo
`digital signals, tWo set-top boxes each having MPEG decod
`ers may be needed to process the tWo digital signals.
`HoWever, such an approach results in signi?cant cost to the
`consumer.
`US. Pat. No. 5,469,206 to Strubbe et al. discloses a
`system that receives compressed audio/video programming
`from a digital transmission system and having, for example,
`MPEG and MUSICAM formats. FIG. 1 of Strubbe et al.
`discloses a system having a ?rst RF decoder 10 in a VCR
`and a second RF decoder 15 in a television receiver. As
`shoWn in FIG. 2 of Strubbe et al., the RF decoders 10 and
`15 each include a decompressor 8 that decompresses the
`program data to provide audio and video television pro
`gramming. The decoded signals are output from the respec
`tive RF decoders to a picture-in-picture (PIP) circuit 30 that
`outputs the tWo program sources in a PIP format to a display
`25. Hence, tWo decoders are still needed for PIP processing,
`one in the VCR and the second in the television receiver,
`requiring extensive modi?cation or purchases by the con
`sumer of neW VCR’s and televisions.
`US. Pat. No. 5,361,098 to Lucas discloses a system for
`producing a reduced-siZe (mean-only) image Within a full
`siZe image for a picture-in-picture inset from compressed
`digital data. FIG. 2 shoWs a mean-only decode section 20
`including a demultiplexer 22 that separates out Y, U, V mean
`value components from a compressed video stream, and
`decoders 24A, 24B and 24C that reconstruct the Huffman
`encoded luminance and chrominance data from the respec
`tive Y, U, V mean value components. The mean-only decode
`section 20 also includes circuitry 26 that creates a 1/16 size
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`means-only image from the reconstructed data. Thus, Lucas
`still requires the additional circuitry of the mean-only
`decode section 20 to provide PIP capabilities from
`compressed, digital data.
`Hence, implementation of PIP or POP as a digital video
`netWork feature has required modi?cation of existing set-top
`devices to add extra decoders to provide the necessary
`processing of the second digital signal for the picture-in
`picture inset. Alternately, implementation has required
`modi?cations to the televisions or VCRs to simultaneously
`process tWo or more digital video signals.
`
`DISCLOSURE OF THE INVENTION
`
`There is a need for an arrangement (apparatus and
`method) for implementing Picture-in-Picture (PIP) and
`Picture-on-Picture (POP) capabilities for digital video sys
`tems.
`There is also a need for an arrangement for adding PIP and
`POP capabilities to a digital entertainment terminal Without
`any hardWare modi?cations to the digital entertainment
`terminal or to a conventional television.
`There is also a need for an apparatus having an MPEG
`decoder capable of processing tWo digital video data streams
`of MPEG-encoded data for PIP and POP processing.
`According to one aspect of the present invention, an
`apparatus includes a digital video processor decompressing
`a ?rst stream of compressed, digital data representing a ?rst
`video program into decompressed ?rst video data having a
`?rst resolution. An application processor partially decom
`presses a second stream of compressed, digital data repre
`senting a second video program into decompressed second
`video data having a second resolution less than the ?rst
`resolution. The digital video processor also outputs a video
`signal representing a frame of the ?rst video data having a
`portion overlaid by the decompressed second video data.
`In a preferred implementation of this apparatus, the appli
`cation processor is a general purpose processor and is
`capable of executing different softWare or ?rmWare appli
`cations in conjunction With the partial decompressing of the
`second stream. Hence, the apparatus of the present invention
`can be easily implemented Within an existing digital enter
`tainment terminal having a microprocessor Without any
`hardWare modi?cations, for example by merely loading
`softWare having the routine for partially decompressing into
`memory accessible by the microprocessor.
`Another aspect of the present invention provides a method
`of generating a video signal of ?rst and second video
`programs, including the steps of receiving ?rst and second
`MPEG-encoded streams carrying the ?rst and second video
`programs, respectively. The ?rst MPEG-encoded stream is
`decoded in an MPEG decoder and outputting as
`decompressed, ?rst digital data carrying the ?rst video
`program. The method also includes partially decoding the
`second MPEG-encoded stream and generating second digi
`tal data carrying a limited-resolution representation of the
`second video program, combining the ?rst and second
`digital data in a video memory, and outputting from the
`video memory a video signal carrying a frame of the
`combined data. The partial decoding of the second MPEG
`encoded stream enables the ?rst and second video programs
`to be displayed from the single video signal Without the need
`for an additional decoder.
`Still another aspect of the present invention provides a
`digital entertainment terminal comprising an application
`processor receiving multiplexed digital data carrying ?rst
`and second streams of compressed, digital data representing
`
`ASUS Exhibit 1006 - Page 10
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`

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`3
`?rst and second programs, respectively. The ?rst and second
`streams have ?rst and second identi?ers, respectively, and
`the application processor outputs the ?rst stream of com
`pressed digital data and a portion of the second stream of
`compressed, digital data in response to the respective ?rst
`and second identi?ers. The digital entertainment terminal
`also includes a digital video processor decompressing at
`least the ?rst stream into ?rst decompressed video data
`representing the ?rst program. The digital video processor
`combines the ?rst decompressed video data With second
`decompressed video data generated from the portion of the
`second stream and outputs the combined ?rst and second
`video data as a video signal representing a video frame
`simultaneously displaying at least portions of said ?rst and
`second video programs. According to this aspect of the
`present invention, the portion of the second stream is par
`tially decompressed into the second decompressed video
`data by one of the application processor and the digital video
`processor. Hence, the digital video processor may process
`both ?rst and second decompressed video data by partially
`decompressing the portion of the second stream. Alternately,
`the application processor may execute softWare to partially
`decompress the portion of the second stream.
`According to another aspect of the present invention, an
`apparatus comprises an MPEG decoder. This decoder
`decompresses a ?rst stream of compressed, digital data into
`?rst video data having a ?rst resolution. The decoder also
`partially decompresses a second stream of compressed,
`digital data into second video data having a second resolu
`tion less than the ?rst resolution. The ?rst and second video
`data represent ?rst and second video programs, respectively.
`An overlay controller receives the ?rst and second video
`data, and in response outputs a video frame signal simulta
`neously displaying at least portions of the ?rst and second
`video programs. Hence, the apparatus uses a single MPEG
`decoder to obtain ?rst and second video data representing
`?rst and second video programs, respectively, and an over
`lay controller to simultaneously display at least portions of
`the ?rst and second video programs. The MPEG decoder
`performs the partial decompression of the second stream
`during idle intervals betWeen frames from the ?rst stream of
`compressed, digital data.
`Additional objects, advantages and novel features of the
`invention Will be set forth in part in the description Which
`folloWs, and in part Will become apparent to those skilled in
`the art upon examination of the folloWing or may be learned
`by practice of the invention. The objects and advantages of
`the invention may be realiZed and attained by means of the
`instrumentalities and combinations particularly pointed out
`in the appended claims.
`
`BRIEF DESCRIPTION OF DRAWINGS
`Reference is made to the attached draWings, Wherein
`elements having the same reference numeral designations
`represent like elements throughout and Wherein:
`FIG. 1 is a block diagram of a digital video netWork
`supplying multiplexed steams of compressed, digital data to
`a customer premises.
`FIG. 2 is a diagram illustrating the transport layer protocol
`of the compressed, digital data from the digital video net
`Work of FIG. 1.
`FIG. 3 is a block diagram of the customer premises
`equipment in the netWork of FIG. 1 including the digital
`entertainment terminal according to one embodiment of the
`present invention.
`FIG. 4 is a block diagram of the netWork interface module
`of FIG. 3.
`
`15
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`FIG. 5 is a block diagram of the digital entertainment
`terminal according to another embodiment of the present
`invention.
`FIGS. 6A and 6B are diagrams illustrating MPEG decod
`ing and inverse scanning, respectively.
`FIG. 7 is a How diagram illustrating the process of
`?ltering an ATM stream to obtain a partial MPEG-stream for
`limited resolution processing.
`FIG. 8 is a diagram shoWing memory regions in the
`memory elements of FIG. 3.
`FIG. 9 is a time sequence diagram illustrating dual-video
`processing by an MPEG decoder according to an embodi
`ment of the present invention.
`FIG. 10 is a diagram shoWing a display structure of a
`primary image and a secondary (PIP) image overlying the
`primary image.
`
`BEST MODE FOR CARRYING OUT THE
`INVENTION
`
`According to the present invention, the dedicated decoder
`circuitry in the digital entertainment terminal (DET) Will
`fully decompress one video stream for the primary picture,
`in the normal manner. An additional decoder arrangement,
`described beloW, Will decode a portion of the video stream
`data of a selected secondary program, for use as the video
`inset for picture-in-picture. In one embodiment of the
`invention, the general purpose microprocessor controlling
`the digital entertainment terminal Will run a partial or
`reduced-set decoding application to decode the limited por
`tion of the secondary video signal. In another embodiment,
`idle intervals that occur in the dedicated decoder circuitry
`betWeen processing frames of the primary compressed data
`stream are used to partially process the limited portion of the
`secondary video signal. Hence, no additional hardWare is
`necessary to execute the picture-in-picture (PIP) feature in
`existing digital entertainment terminals, and implementation
`of the PIP feature requires only doWnloading of an appro
`priate decoder application into the DET.
`A high-level description Will ?rst be provided of an
`exemplary digital video netWork supplying the primary and
`secondary compressed data streams, folloWed by a detailed
`description of the customer premises equipment including
`the DET performing the PIP processing.
`FIG. 1 is a block diagram of a digital video netWork 10
`supplying multiplexed steams of compressed, digital data
`from a video information provider (VIP) 12 to customer
`premises equipment 14. The netWork 10 provides transport
`for broadband services including broadcast video and IMTV
`type services, such as video on demand. The netWork 10 also
`provides interactive text services and voice telephone ser
`vices. In addition, the netWork doWnloads softWare to the
`DET, including softWare for performing PIP processing by
`partially decompressing a secondary compressed data
`stream. A more detailed description of one implementation
`of the netWork 10 and the doWnloading of softWare to the
`DET is disclosed in commonly-assigned, copending appli
`cation No. 08/498,265, ?led Jul. 3, 1995, US. Pat. No.
`5,666,293, entitled DOWNLOADING OPERATING SYS
`TEM SOFTWARE THROUGH A BROADCAST CHAN
`NEL (attorney docket 680-083D), the disclosure of Which is
`incorporated in its entirety by reference.
`The illustrated netWork 10 comprises an ATM backbone
`netWork 16 and a local loop netWork 18. The ATM backbone
`netWork 16 includes optical ?bers 20 that transport ATM cell
`streams from the VIP 12 to an ATM edge device (not
`
`ASUS Exhibit 1006 - Page 11
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`5,847,771
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`shown). ATM cell streams output from the VIP 12 may carry
`broadcast programming as compressed, digital data such as
`MPEG-encoded data. Alternately, the ATM cell streams may
`carry softWare programming to be doWnloaded to the cus
`tomer premises equipment 14.
`The local loop netWork includes host digital terminals
`(HDT’s) 22, optical netWork units (ONU) 24, tWo-Way
`optical ?ber pairs 26 coupling the HDT’s 22 and optical
`netWork units 24, and coaxial cables 28 and/or tWisted Wire
`pairs connecting the ONU 24 to the subscriber premises
`equipment 14. Broadcast services are controlled by control
`processor elements (not shoWn) Within the HDT’s 22 and a
`video administration module (not shoWn). ATM cell streams
`carrying broadcast programming are distributed throughout
`the ATM netWork 16 to a large number of the host digital
`terminals (HDT’s) 22.
`Signaling communications takes place betWeen the cus
`tomer premises equipment 14 and the serving HDT 22. The
`upstream signaling communications enables a user to order
`a speci?c service from the VIP 12, for example request
`pay-per-vieW or IMTV services.
`The ATM netWork 16 includes at least one ATM sWitch
`(not shoWn) for interactive multimedia television (IMTV)
`services. A subscriber Wishing to initiate an IMTV session
`interacts With a level 1 gateWay 30 Which in turn commu
`nicates With a PVC controller (not shoWn) to obtain the
`requisite bandWidth through the ATM sWitch.
`Although only one VIP 12 is shoWn in FIG. 1, a plurality
`of VIPs and service information providers providing video,
`text, softWare, etc., may be connected to the netWork 10.
`According to the disclosed embodiment, the ONU 24 sup
`plies an ATM cell stream speci?ed by the HDT 22 to the
`customer premises equipment 14 at 51.84 MBits/s according
`to a CAP-16 physical layer protocol. This bit stream con
`tains ATM cell streams (virtual channels) for a number of
`selected programs, e.g., to provide service to several termi
`nals or tWo or more program signals to one terminal for PIP
`processing.
`In normal operation, the broadcast netWork supplies at
`least a selected program channel to the customer premises
`equipment 14 including a netWork interface module (NIM)
`50 and a digital entertainment terminal (DET) 52, shoWn in
`FIG. 3. The NIM 50 and the DET 52 are collectively referred
`to as the set-top box or set-top terminal. The set-top terminal
`processes information from the selected channel to produce
`signals capable of presenting information from that channel
`to a user in humanly perceptible form, eg to drive a
`standard television set 54 to display selected video program
`ming. The NIM provides the actual physical connection to
`the netWork and the transport protocol processing (e.g.
`ATM). The DET 52 performs the actual decoding to produce
`the output signals from the information. The DET 52 also
`includes the primary intelligent control processor for overall
`control of the operation of the DET.
`Since the netWork 10 utiliZes ATM transport, the VIP 12
`operates a system 12 including an encoder system. The
`encoder includes an ATM multiplexer (mux) (not shoWn)
`and a video encoder that supplies MPEG2 encoded packets
`of video program data. The VIP’s system also includes a
`data module that receives a repeating or cyclical sequence of
`one or more data ?les from a data server. The data ?les may
`be con?guration data or softWare executable by the DET, for
`example PIP processing softWare. The data module com
`presses the data ?les using MPEG2 compression, and sup
`plies a repeating sequence of MPEG2 packets to the ATM
`multiplexer. Hence, ATM cell streams transported by the
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`ATM netWork 16 may carry a plurality of video program
`data or executable softWare.
`FIG. 2 is diagram shoWing the protocol structure for the
`data supplied to the customer premises equipment 14
`according to the Open Systems Interconnection (OSI) Ref
`erence Model. The CAP 16 layer is the physical layer
`betWeen the ONU 24 and the customer premises equipment
`14. The CAP 16 layer 32 uses CAP 16 modulation and
`forWard error correction, and occupies bandWidth beloW 30
`MHZ, With approximately 2 MHZ of bandWidth reserved for
`upstream signaling from the customer premises equipment
`14. A transmission convergence protocol 34 using STS-1
`protocol is used as the data link layer above the physical
`layer 32. The next layer in the protocol structure is the ATM
`transport layer 36, including the ATM headers and payloads,
`then the AAL5 layer 38, described beloW.
`The MPEG2 transport layer 40 includes MPEG2 program
`transport streams corresponding to a speci?ed Program
`Identi?er (PID) value and having a Program Clock Refer
`ence (PCR) value. The transport layer 40 may include a
`plurality of MPEG2 streams, including video, audio, text,
`etc. for a speci?ed program. The MPEG2 elementary stream
`speci?es an individual packetiZed elementary stream (PES)
`of MPEG2 compressed data, for example a video frame,
`audio data, or executable softWare data.
`Hence, FIG. 2 illustrates the encoding, compression, and
`encapsulation of data at the VIP headend before transmis
`sion on the netWork 10, and the corresponding assembling
`and decompression at the customer premises equipment 14.
`In ATM, transfer is asynchronous in the sense that the
`recurrence of cells that contain information from any par
`ticular sender is not necessarily periodic. Each device 12, 30
`using an ATM netWork 16 submits a cell for transfer When
`they have a cell to send, not When they have an assigned or
`available transmission time slot. HoWever, the ATM cells
`may ride in synchronous slots on a high-speed time division
`multiplexed media, such as a SONET optical ?ber. ATM
`alloWs any arbitrary information transfer rate up to the
`maximum supported by the ATM netWork, simply by trans
`mitting cells more often as more bandWidth is needed.
`In ATM, information is organiZed into cells having a ?xed
`length and format. Each cell includes a header, primarily for
`identifying cells relating to the same virtual connection, and
`an information ?eld or “payload”. Under presently existing
`ATM standards, a 53 byte ATM cell includes a cell header
`consisting of 5 bytes and a payload consisting of 48 bytes of
`payload data. The ATM cell header information includes a
`virtual path identi?er (VPI) and a virtual circuit identi?er
`(VCI) to identify the particular communication to Which
`each cell relates. The speci?c format of the ATM cell is
`described, for example, in the ATM User Network Interface
`Speci?cation, Version 3.0, published by The ATM Forum,
`Mountain VieW, Cali., also published by Prentice Hall, the
`disclosure of Which is incorporated in its entirety by refer
`ence.
`The typical ATM cell format in layer 36 of FIG. 2 includes
`a header section and a payload section. The ?rst 8-bit byte
`of the header section includes a 4-bit GFC Word Which
`provides access control. The ?rst byte of the header section
`also includes the loWer four bits of an 8-bit virtual-path
`identi?er (VPI). The second byte of the header section
`includes the upper four bits of the VPI and the ?rst four bits
`of a 16-bit virtual circuit identi?er (VCI). The third byte
`includes the next eight bits of the VCI. The fourth byte of the
`header section includes the last four bits of the VCI; a 3-bit
`payload type indicator (PT); and a cell loss priority bit
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`ASUS Exhibit 1006 - Page 12
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`(CLP). The ?fth byte of the header section includes an 8-bit
`header error check (HEC) Word. Bytes 6 to 53 carry infor
`mation and form the ATM cell payload section.
`The ATM multiplexer at the system operated by VIP 12
`performs an ATM adaptation function Which converts the
`MPEG2 transport packets of layer 40 into ATM cells. The
`ATM multiplexer also performs a multiplexing function to
`combine cells streams carrying payload data from a number
`of sources into one higher rate bit stream.
`In ATM based netWorks of the type under consideration
`here, the MPEG2 bit streams are converted into cellular
`payload data, and cell headers are added. A number of
`techniques can be used to adapt the transport packets into
`ATM cells, and certain preferred techniques are described
`beloW by Way of example.
`Each MPEG packet consists of 188 bytes, Whereas each
`ATM cell includes 48 bytes of payload data. The ATM
`multiplexer Which map the MPEG packets into ATM cells
`preferably uses tWo different adaptations to encapsulate
`MPEG2 packets in ATM cells. The ?rst adaptation maps one
`188 byte MPEG packet into ?ve ATM 48-byte cell payloads,
`shoWn as layer 38. The second adaptation maps tWo 188 byte
`MPEG packets into eight ATM 48 byte cells payloads.
`MPEG packets of 188 bytes map ef?ciently into ATM
`cells if pairs of packets are mapped into 8 cells. HoWever, a
`delay is imposed on mapping of a ?rst cell While Waiting for
`the second cell in the pair. To minimiZe jitter at the decoder
`at the customer premises, the packets carrying the PCR
`values need to be encoded and transported quickly. To avoid
`delaying ?rst packets containing a PCR While processing a
`second packet, the present system maps ?rst packets con
`taining a PCR immediately, using the ?ve cell adaptation
`procedure. In a typical video transmission, the PCR is
`present in approximately 10 out of every 4000 MPEG2
`packets. Also, at least some of those 10 packets Will arrive
`as the second packet of a pair. Consequently, only a very
`small number of packets are mapped using the less ef?cient
`5 -cell adaptation. In addition, it is possible for some systems
`to map tWo MPEG2 transport packets into 8 cells in all cases
`regardless of Whether a PCR is contained in the ?rst of the
`tWo packets.
`The MPEG real time encoder in the system operated by
`VIP 12 supplies a stream of MPEG2 packets to the ATM
`multiplexer. The ATM multiplexer checks the ?ags in the
`adaption ?eld (if any) in the ?rst packet to determine if that
`packet includes a program clock reference (PCR) value. The
`ATM multiplexer applies the 5 cell adaptation to ?rst
`packets containing a program clock reference (PCR) value.
`The ATM multiplexer applies the 8 cell adaptation to pairs
`of cells Wherein the ?rst packet does not contain a program
`clock reference (PCR) value. Packets containing private
`data, such as applications and operating system softWare,
`Will not contain a PRC ?ag.
`For each type of adaptation, the ATM multiplexer Will ?rst
`convert the source packet or pair of packets into a single
`ATM adaptation layer 5 (AAL5) packet of layer 38. As part
`of this conversion, the mux Will add an AAl5 trailer, either
`at the end of the single packet or at the end of the pair of
`packets. The actual trailer consists of 8 bytes of data,
`including 4 bytes of cyclic redundancy check (CRC) data,
`user information (eg length), etc.
`For a 5 cell adaptation, the AAL5 packet consists of a
`single MPEG packet of 188 bytes and an 8 byte AAL5
`trailer, for a total of 196 bytes. To map this packet into ATM
`cells, the AAL5 packet is also padded With 44 bytes after the
`trailer, for a total of 240 bytes of payload data. The ATM
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`mux breaks the AAL5 packet (240 bytes) doWn into ?ve
`48-byte payloads (SAR-PDU) and attaches appropriate 5
`byte headers to each payload to thereby form ?ve 53-byte
`ATM cells in layer 36.
`The header of all ?ve of the ATM cells Will contain the
`VPI/VCI value assigned to the particular communication.
`For example, for the broadcast service combined With the
`softWare doWnloading, the assigned VPI and VCI value
`Would correspond to netWork logical channel 0. For the
`video and audio portion of the program guide service, the
`packets Would periodically contain a PCR value and peri
`odically Would go through the 5 cell adaptation in the normal
`manner. The header of the ?rst of the ?ve cells also has a bit
`designated“AAU” Which has a value of“0” to identify that
`cell as the ?rst cell. The header of the ?fth cell Will have an
`AAU bit value of “1” to identify that cell as the last cell.
`For an 8 cell adaptation, the AAL5 packet consists of tWo
`MPEG packets of 188 bytes and an 8 byte AAL5 trailer, for
`a total of 384 bytes. The ATM mux breaks the AAL5 packet
`(384 bytes) doWn into eight 48-byte payloads and attaches
`appropriate 5 byte headers to each payload to thereby form
`eight 53-byte ATM cells.
`The header of all eight of the ATM cells Will contain the
`VPI/VCI value assigned to the particular communication.
`Continuing the above example, if the MPEG data relates to
`the program guide or the operating system doWnloading
`service, the assigned VPI and VCI values Would identify
`logical netWork channel 0 as in the above discussed example
`of the ?ve-cell adaptation. The header of the ?rst of the eight
`cells Will have an AAU bit value of“0” to identify that cell
`as the ?rst cell. The header of the eighth cell Will have an
`AAU bit value of “1” to identify that cell as the last cell.
`As noted above, each cell of a particular stream Will have
`a header Which contains a virtual path identi?er/virtual
`circuit identi?er (VPI/VCI) to identify the virtual circuit that
`the cells pertain to. All MPEG packets for a given program,
`Whether video, audio or data, Will be mapped into ATM cells
`having the same VPI/V CI. Conversely, cells having a given
`VPI/VCI W