(12) United States Patent
`US 6,253,375 B1
`(10) Patent N0.:
`
`Gordon et al.
`(45) Date of Patent:
`Jun. 26, 2001
`
`US006253375B1
`
`(54) SYSTEM FOR INTERACTIVELY
`DISTRIBUTING INFORMATION SERVICES
`
`(75)
`
`Inventors: Donald Gordon, Pacific Grove;
`-
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`Yama (
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`Cranbury; Danny Chm, Prlnceton
`Junctlon, both of NJ (US)
`
`(73) Assignee: DIVA Systems Corporation, Redwood
`City, CA (US)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U'S'C' 154(b) by 0 days'
`
`(21) Appl. N0.: 08/984,710
`.
`Flledi
`
`Dec- 3, 1997
`
`(22)
`
`60
`
`)
`
`(
`
`Related US. Application Data
`P H l
`l'
`t'
`N . 60034489 fil d
`13395101121 app lea Ion
`0
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`7
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`on an
`
`’
`
`(51)
`Int. Cl.
`..................................................... H04N 7/173
`
`(52)
`725/88; 725/95
`(58) Field of Search ..................................... 345/326, 327,
`348/6’ 7’ 10’ 12’ 13; 395/209‘47’ 20049;
`455/3'1’ 4’1’ 4’2’ 5'1’ 6'1’ 62’ H04N 7/10’
`7/14’ 7/16’ 7/173
`
`(56)
`
`27:38:33;
`4’573’072
`4,602,279
`4,623,920
`4,763,317
`4,769,833
`
`.
`References Clted
`U.S. PATENT DOCUMENTS
`.
`i/13:: glmple etlal' """"""""""""" £332
`
`2%986 Fifi: a ‘
`358/86
`
`7/1986 Freeman """""" 358/86
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`
`8/1988 Lehman et al.
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`9/1988 Farleigh et al.
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`
`4,792,849
`12/1988 McCalley et al.
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`5,014,125
`.. 358/86
`5/1991 Pocock et al.
`
`5,070,400
`.. 358/84
`12/1991 Lieberman
`
`5917:9213 Egg: Ifiapglet at Ml
`~~ 328%?)
`..
`,
`,
`ra ey e a.
`.. 358/86
`5,181,106
`1/1993 Sutherland
`
`1/1993 Takano ................................... 358/86
`5,182,640
`5,235,619
`8/1993 Beyers, 11 et al.
`.................... 375/38
`
`...... 358/85
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`4/1994 Withers et al.
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`
`10/1994 Banker et al. ................ 348/7
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`10/1994 Wasilewski et al.
`.................. 370/73
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`5,400,402
`3/1995 Garfinkle ............................... 380/20
`5,414,455 *
`5/1995 Hooper et al.
`348/7
`
`~~ 348/13
`59481542 *
`1/1996 LOgStOH 6t a1~
`
`31332 goafritykl ~~~~~~~~~~
`gagggagz
`333;;
`,
`,
`ar n e
`
`5,550,576
`8/1996 Klosterman
`348/6
`12/1996 Florin et al. .............. 348/7
`5,583,560
`
`5,586,264 * 12/1996 Belknap et al.
`..
`395/200.08
`........ 370/233
`5,671,217
`9/1997 Adams et al.
`
`6/1998 Metz etal. ...................... 395/20079
`5,768,539
`
`* cited by examiner
`Primary Examiner—Chris Grant
`(74) Attorney, Agent, or Firm—Thomason, Moser &
`Patterson, LLP
`
`ABSTRACT
`(57)
`An interactive information distribution system includes ser-
`vice provider equipment
`for generating an information
`stream that is coupled to an information channel and trans-
`mitted to subscriber equipment. The service provider also
`generates a command signal that is coupled to a command
`channel and transmitted to the subscriber equipment. The
`service provider also receives information manipulation
`requests from the subscriber via a back channel. A commu-
`nication network supporting the information channel, com-
`mand channel and back channel is coupled between the
`serVice I’rOVi‘ler equipment and the subscriber equipment
`
`7 Claims, 5 Drawing Sheets
`
`CABLE TELEVISION
`125
`
`SIGNALSOEZgE
`H110
`H1241
`9
`
`102
`
`104
`
`INFgERmTFLON
`
`
`
`103
`
`106
`VIDEO
`CABLE
`SESSION
`MANAGER — TRANSPORT
`SUBSYSTEM
`109
`
`NETWORK
`MANAGER
`
`“4
`
`100
`
`051
`
`
`SETTOP \
`TERMINAL 118
`122
`C]
`
`120
`
`
`
`1°52 SUBSCRIBER EQU PMENT
`
`SUBSCRIBER'J1242
`EQUIPMENT
`
`
`
`BACK OFFICE
`SUBSYSTEMS f1 1 6
`
`
`1053
`
`SUBSCRIBER'41243
`EQUIPMENT
`
`SUBSCRIBER
`EQUIPMENT
`
`105n
`
`124n
`
`BBiTV EX2171
`
`DISH v. BBiTV
`
`IPR2020-01267
`
`BBiTV EX2171
`DISH v. BBiTV
`IPR2020-01267
`
`

`

`US. Patent
`
`Jun.26,2001
`
`SheetlrofS
`
`US 6,253,375 B1
`
`59
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`

`

`US. Patent
`
`Jun. 26, 2001
`
`Sheet 2 0f 5
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`US 6,253,375 B1
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`

`US. Patent
`
`Jun. 26, 2001
`
`Sheet 3 0f5
`
`US 6,253,375 B1
`
`SESSION
`SECURITY
`
`ROURNE
`w
`
`302
`
`START
`
`04
`
`SELECT
`A FIRST (ACTIVE)
`DVM
`
`
`
`
`
`
`
`
`
`
`
`INSTRUCTING
`THE AFFECTED SET TOP TERMINAL
`
`
`TO DECODE FROM THE SECOND DVM
`
`306
`
`MATCH
`
`FIRST DVM OUTPUT
`WITH SECOND (STANDBY)
`DVM OUTPUT
`
`
`
`

`

`US. Patent
`
`Jun. 26, 2001
`
`Sheet 4 0f5
`
`US 6,253,375 B1
`
`BACKPLANE
`
`408
`
`400
`
`TO/FROM
`NETWORK
`
`SUPPORT
`CIRCUITS
`
`
`g)
`
`
`410
`
`
`
`
`
`
`4 16
`
`
`
`l-hI
`
`
`
`APPLICATION PROGRAM(S)
`
`CONFIGURATION DATABASE
`
`SUBTENDING
`SUBSCRIBER DATABASE
`
`NAVIGATOR MENU TREE
`
`SESSION STRUCTURES
`
`OPERATING SYSTEM
`
`412
`
`414
`
`418
`
`20
`
`FIG. 4
`
`

`

`US. Patent
`
`Jun. 26, 2001
`
`Sheet 5 0f5
`
`US 6,253,375 B1
`
`L
`
`TO/FROM
`CABLE TRANSPORT NETWORK
`
`DIPLEXER
`
`
`
`MODULATOR
`
`COMMAND
`DEMODULATOR
`
`ANALOG
`CABLE TELEVISION
`SIGNAL DEMODULATOR
`
`INFORMATION
`DEMODULATOR
`
`516
`
`SUPPORT
`CIRCUITS
`
`FROM
`INPUT DEVICE
`
`FIG. 5
`
`

`

`US 6,253,375 B1
`
`1
`SYSTEM FOR INTERACTIVELY
`DISTRIBUTING INFORMATION SERVICES
`
`This application claims benefit of US. provisional patent
`application 60/034,489, filed Jan. 13, 1997, the disclosure of
`which is herein incorporated by reference.
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The present invention relates to a system for delivering
`interactive information services, such as video, audio,
`library,
`interactive games, and the like to one or more
`subscribers. More particularly,
`the invention relates to a
`system for establishing a multi-channel communicative con-
`nection between a subscriber’s set top terminal and a service
`provider and then managing the communications necessary
`to deliver interactive information services to the subscriber
`
`(s).
`2. Description of the Background Art
`Recent advances in digital signal processing techniques
`and,
`in particular, advancements in digital compression
`techniques, have led to a plethora of proposals for providing
`new digital services to a subscriber’s home via existing
`telephone and coaxial cable networks. For example, it has
`been proposed to provide hundreds of cable television
`channels to subscribers by compressing digital video, trans-
`mitting the compressed digital video over conventional
`coaxial cable television cables, and then decompressing the
`video at the subscriber’s set top terminal. Another proposed
`application of this technology is a movie-on-demand video
`system in which a subscriber communicates directly with a
`video service provider via telephone lines to request a
`particular video program from a video library and the
`requested video program is routed to the subscriber’s home
`via telephone lines or via the coaxial television cables for
`immediate viewing.
`However, these present movie-on-demand video systems
`are not truly interactive systems wherein a subscriber can
`selectively access a large audio, video or data library and
`control the presentation of the selected information on a
`real-time basis, as when a video program is played using a
`video cassette recorder (VCR). Most of the presently avail-
`able systems have a simple control interface that permits
`subscribers to merely order information without any further
`control of the presentation of the information. Other, more
`sophisticated systems, have a control interface that contains
`more complex commands such as start, stop, pause, fast-
`forward and rewind to permit rudimentary control of the
`presentation of the information. However, these systems use
`conventional signaling and information routing networks
`that are relatively slow to react to the commands, e.g., the
`latency between the instant an interactive function is
`requested and when that function takes effect is extremely
`long. Furthermore,
`the set
`top terminals used by these
`systems contain complex and costly electronics to facilitate
`processing of the complex commands. Additionally, these
`systems use a conventional cable television network
`architecture, where a central data server transmits data to a
`plurality of head end subsystems which in turn propagate
`various subsets of the data to an individual or a multiplicity
`of set top terminals. The servers in such systems perform
`much of the control functions and, as such,
`the latency
`arising from sending control commands through the head
`end to the server is substantial.
`
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`real-time interaction (with relatively short latency) between
`the subscriber and the service provider at any time during the
`presentation of requested information.
`
`SUMMARY OF THE INVENTION
`
`The disadvantages heretofore associated with the prior art
`are overcome by the present invention. The present inven-
`tion is a system for interactively distributing information
`services. The system contains an information server, a video
`session manager, a bi-directional cable transport network,
`and subscriber equipment (e.g., a set top terminal, an input
`device, and a display device).
`The system uses three independent communications chan-
`nels to facilitate distribution and interactive control of the
`
`information distribution process. Specifically, an informa-
`tion channel propagates program information and a com-
`mand channel propagates control information from the ser-
`vice provide to the subscriber equipment, and a back channel
`propagates command and control
`information from the
`subscriber equipment to the service provider. The informa-
`tion channel may also be utilized to transport control infor-
`mation to the subscriber equipment. Consequently, the ser-
`vice provider sends through the command and/or
`information channels selection menus to the subscriber
`
`equipment such that a subscriber can select a particular
`program. The program selection request
`is propagated
`through the back channel to the service provider. The service
`provider then sends the program through the information
`channel for display on the subscriber equipment. The sub-
`scriber can manipulate (e.g., fast-forward, pause, rewind,
`perform context based branching and the like) the presen-
`tation via commands sent from the subscriber equipment to
`the service provider.
`More specifically, the server provides a video session
`manager with a plurality of program streams that generally
`comply with the MPEG-2 transport protocol. The program
`streams are generated using a common, high accuracy clock
`signal (synchronization clock) such that
`the data in the
`plurality of streams is synchronous. The video session
`manager interacts with the server to request particular infor-
`mation program streams in response to subscriber demands.
`Once a subscriber requests use of the service provider
`navigator to facilitate selection of viewable programming,
`the video session manager opens a “session” for a given
`subscriber and sends requested program streams through the
`cable transport network to the subscriber’s set top terminal
`via the information channel.
`
`To provide real-time interactive control of the information
`presentation to the subscriber, the subscriber, through their
`input device (remote control), may order, start, stop, fast-
`forward, rewind, pause and branch from or to any informa-
`tion stream that is resident on the server subsystem. As such,
`the system of the present invention provides the customer
`with all of the interactive commands that are generally
`available on a conventional video cassette recorder.
`
`Additionally, the user can open multiple sessions such that
`multiple information streams may be started and stopped
`and interactively controlled at any time. Such interaction is
`facilitated by the system because the system is synchronized
`from end-to-end. That is, the server provides the synchro-
`nization clock to which all subsystems of the invention are
`synchronized. The system synchronization extends to the
`cable transport network and the subscriber’s set top termi-
`nal.
`
`Therefore, there is a need in the art for a cost effective,
`interactive information distribution system that provides
`
`the synchronization clock is used by the
`In particular,
`video session manager to modulate all of the data streams
`
`

`

`US 6,253,375 B1
`
`3
`such that each transmitted stream is synchronized with other
`streams. Furthermore, the set top terminals recover timing
`from the synchronized data bits within the received stream;
`thus,
`the set top terminals are also synchronized to the
`synchronization clock. As such, when a subscriber changes
`from one program to another, there is no resynchronization
`delay before the different program is available for display.
`Consequently,
`the latency between when a command is
`entered and when it is implemented is relatively short. Thus,
`a subscriber can have multiple sessions open and switch
`from one to another without substantial delay after each
`session change.
`To reduce the cost associated with transmission and
`
`the system of the
`presentation of each program stream,
`present invention avoids encrypting all of the information
`that is sent to the set top terminals. System security, without
`encryption, is provided by randomly assigned and altered
`program identification numbers (PID). Specifically, when a
`session is started by a subscriber request, the set top terminal
`is assigned a unique session number. Additionally, the set
`top terminal has an assigned identification number (TID).
`This TID is compared to a TID stored in the system such that
`the user identification is confirmed. Periodically, the TID
`numbers are automatically updated on a random basis to
`insure system security.
`The requested information is multiplexed onto an infor-
`mation channel, e.g., ten streams of 2.6 Mbit/sec data are
`carried by a single information channel to a plurality of set
`top terminals (a neighborhood). A neighborhood may be
`serviced by more than one channel to further increase the
`transmission flexibility. For instance,
`the terminals are
`dynamically allocated to the channels such that 10 terminals
`can simultaneously share one channel or three terminals can
`receive 5.2 Mbit/sec data, and so on. Consequently, any
`combination of data rates is permissible and the data rate for
`a particular subscriber depends upon the requested informa-
`tion. Some programs, such as basketball games, may require
`a large transmission bandwidth to avoid compression
`anomalies. The present invention provides dynamic data rate
`flexibility to provide subscribers with the best signal quality
`possible.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The teachings of the present invention can be readily
`understood by considering the following detailed descrip-
`tion in conjunction with the accompanying drawings, in
`which:
`
`FIG. 1 depicts a high-level block diagram of an interactive
`information distribution system in accordance with the
`present invention;
`FIG. 2 depicts block diagram of a video session manager;
`FIG. 3 depicts a flow diagram of a session security
`routine;
`FIG. 4 depicts a block diagram of the video session
`manager computer; and
`FIG. 5 depicts a detailed block diagram of a set top
`terminal.
`
`To facilitate understanding, identical reference numerals
`have been used, where possible,
`to designate identical
`elements that are common to the figures.
`DETAILED DESCRIPTION
`
`The invention is a cost effective, interactive information
`distribution system that provides an individual or a plurality
`of subscribers with information such as multimedia
`
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`programming, audio, video, graphics, and the like. This
`information is available in an “on demand” basis.
`
`Furthermore, the system enables subscribers to control, in
`real-time, the presentation of the information, e. g., requested
`stream can be started, stopped, paused, reversed, fast for-
`warded and branched without substantial latency. The infor-
`mation can be supplied to the subscribers through broadcast,
`where all subscribers receive the same information;
`pointcast, where each subscriber receives specific informa-
`tion that
`is only addressed to a specific subscriber; or
`narrowcast, where a subset of all the subscribers received
`particular information.
`The system as a whole is discussed below in summary
`fashion. Thereafter, each inventive component subsystem of
`the inventive system is individually discussed in detail.
`A. System Overview
`FIG. 1 is high-level block diagram of the interactive
`information distribution system 100 of the present invention.
`The system contains an information server 102, at least one
`video session manager 106, a network manager 114, back
`office subsystems 116, a cable transport network 110, and a
`plurality of subscriber equipment 124. The subscriber equip-
`ment 124 includes a set top terminal 118, an input device
`(e.g., a remote control 120) and a display device 122.
`The information server 102 provides a plurality of pack-
`etized data streams, via path 104, and a synchronization
`clock signal, via path 103,
`to one or more video session
`managers 106 (only one of which is shown). Alternatively,
`the plurality of data streams is multiplexed onto an optical
`fiber (a trunk) and each video session manager is connected
`to the trunk by a “drop line.” The number of video session
`managers is proportional to the number of subscribers being
`serviced by the system, e. g., each video session manager can
`generally service up to 2000 subscribers. The server 102
`provides information (data streams) in response to specific
`information requests from the video session manager that
`are communicated to the server through a communications
`network. The video session manager performs various sys-
`tem command and control functions as well as communi-
`cates the data streams to the cable network. As such, the
`system uses three directional communication channels to
`perform control and communication operations. The video
`session manager may address the streams to be propagated
`to the subscribers in broadcast, narrowcast, or pointcast
`modes.
`
`Specifically, the video session manager modulates each of
`the baseband data streams onto a carrier signal and upcon-
`verts the signal to a transmission frequency that complies
`with conventional cable television (CATV) frequency spec-
`trum. Illustratively, the downstream data modulation is, for
`example, 64-ary quadrature amplitude modulation (QAM)
`and the transmission frequency is in the range 50 to 750
`MHz. Other modulation types and frequency bands maybe
`used. This information is coupled to the cable network via
`path 108 and is carried through the cable network on what
`is referred to as the information channel.
`
`The video session manager 106 also transmits control
`information through a downstream command channel (path
`107) contained within the cable transport network 110 to the
`subscriber equipment 124. This command and control infor-
`mation is transmitted on a carrier in the range 50 to 750 MHz
`using a 1 MHz bandwidth, e.g., the command information is
`frequency multiplexed with the information channel and
`transmitted through the network 110. Furthermore, the sub-
`scriber equipment 124 communicates via a reverse (or back)
`channel to the video session manager 106 through the cable
`
`

`

`US 6,253,375 B1
`
`5
`transport network 110 and the reverse channel path 109.
`There are typically 16 such reverse channels supported by
`each video session manager. Each reverse channel carries,
`for example, a BPSK modulated signal on a carrier in the
`range 5—42 MHZ, where the channel capacity is approxi-
`mately 64 kbps. Other frequency ranges, modulation types
`or channel capacities may be used.
`In addition to the information that can be interactively
`manipulated,
`the system provides for communication of
`conventional cable television signals (analog signals) to the
`subscriber equipment. Specifically, a conventional cable
`signal source 126 (e.g., a conventional cable head end) is
`coupled to one input of a signal summer 128. The other input
`of summer 128 is coupled to path 108 from the video session
`manager 106. As such, the conventional cable signals propa-
`gate to the subscriber equipment to supplement the interac-
`tive information provided by the service provider.
`The cable transport network 110 is typically, but not
`exclusively, a conventional bidirectional hybrid fiber-coax
`cable network. Depending upon the fiber node size, the
`invention requires between two and five available conven-
`tional cable channels (e.g., 6 MHZ bandwidth channels) to
`effectively provide service to approximately 2000 subscrib-
`ers. In addition to the downstream information channels, the
`network must also support the downstream command chan-
`nel and the upstream “back” channel.
`The subscriber equipment 124 is coupled to the cable
`transport network 110 by path 105 (e.g., coaxial cable) and
`contains a set top terminal 118, an input device 120, and a
`display device 122. The set top terminals 118 receive and
`demodulate the downstream signals including those propa-
`gated through both the command channel and the informa-
`tion channel. The set top terminals also optionally demodu-
`late standard cable television signals received from the
`network. Thus, a single set top terminal can be used to
`receive all the cable services provided by the network. The
`set
`top terminals also provide interactive control of the
`information presentation. The presentation is controlled via
`the input device 120, e.g., an infrared (IR), radio frequency
`(RF), or some other remote control unit. The information,
`e.g., audio, video, still photographs, graphics, multimedia
`programs and the like are portrayed on the display device
`122 such as a television, video monitor, stereo system and
`the like.
`
`The network manager 114 manages the system assets,
`provides security measures, and ensures synchronization of
`all system components. The network manager communi-
`cates with all the system components via a communication
`bus architecture 112. This bus may be implemented using a
`conventional ETHERNET or a standard communications or,
`standard networking architecture. The network manager 114
`also communicates with the back office subsystems 116 that
`maintain the subscriber account management software. This
`software performs billing and accounting functions to cor-
`relate the subscriber identification numbers with information
`
`resources that are requested and the price of that information
`resource. Such back office systems do not form any part of
`the present invention; therefore, this system component will
`not be discussed any further, but is mentioned here for
`completeness.
`In operation, each set top terminal is assigned a unique
`identification code and each subscriber has a defined per-
`sonal identification number (PIN). The PINs may be allo-
`cated by family or by family member, e.g., children can have
`different PINs than parents. PIN allocation and management
`is disclosed in commonly assigned US. patent application
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`Ser. No. 08/738,343 filed Oct. 25, 1996 and incorporated
`herein by reference.
`To the subscriber, the default system signal exists from the
`set top terminal for processing by an output device such as
`a television or other equipment depending on the nature of
`the output signal. On the subscriber’s television it may
`appear as predetermined one channel in the plurality of cable
`channels available to the customer. The default signal may
`be presented as a “barker channel” which invites a viewer to
`subscribe to or access the service or, at least, browse through
`a number of available information offerings. The default
`system signal, if in the form of a barker channel or other
`cable channel is continuously broadcast to all subscribers
`and potential subscribers. The barker channel maybe analog,
`digital, or both as set to the set top terminal.
`If interested, the viewer selects entry into the system by
`manipulating the buttons (or joystick) of the remote control
`120. During the selection process, the viewer (now a poten-
`tial subscriber) is presented with an on-screen browser (a
`graphical interface generally known as a navigator) that aids
`the viewer
`in finding information,
`the prices of the
`selections, search aides, and the like. The commands used to
`navigate throughout the various menus are transmitted from
`the set top terminal to the video session manager via the
`back channel. The video session manager responds to cus-
`tomer commands via the downstream command and infor-
`mation channels. When the subscriber executes the
`navigator, the video session manager opens a session for that
`particular subscriber.
`Once a program, for example, a movie, is selected for
`viewing,
`the video session manager 106 associates the
`selected program with the open session for that particular
`subscriber. The subscriber PIN is requested and checked
`against a PIN database managed by the network manager
`114. Also, the set top terminal ID (TID) is checked against
`a database of terminal IDs to ensure that the request is being
`made from an authorized terminal. Each program that is
`available has a set of unique identification numbers or PIDs.
`Thus, when a program is requested,
`the video session
`manager 106 sends the PID to the server 102 along path 103.
`As such, the server recalls the program from memory and
`provides the requested information to the video session
`manager as a packetized data stream. The data stream
`packets are addressed to the appropriate TID and carry the
`PID for the requested program. The video session manager
`processes the data streams for transmission onto the cable
`network and the set top terminal retrieves all the packets
`addressed to its TID. The set top terminal decodes and
`decompresses the data for presentation to the subscriber.
`At any time during the presentation of the requested
`information, the subscriber may request special functions be
`performed. For example, the subscriber can begin another
`session,
`temporarily stopping the previous session.
`Additionally, the customer may stop, pause, rewind, or fast
`forward the information. The subscriber may leave the
`system and return later to watch the program from the
`location where the subscriber interrupted the program. Each
`of these functions is accomplished by manipulating the
`remote control. The set
`top terminal sends the control
`information via the back channel
`to the video session
`
`manager. The video session manager informs the server of
`the control command for implementation as well as informs
`the network manager of the command so that billing can be
`appropriately altered. In this manner, a subscriber is pro-
`vided a real-time, fully functional information-on-demand
`system.
`One important feature of the invention that allows for
`such system flexibility is end-to-end system synchroniza-
`
`

`

`US 6,253,375 B1
`
`7
`the server
`tion. To facilitate end-to-end synchronization,
`uses a high accuracy (level 1) clock signal as a reference
`signal for all server timing. As such, all the data streams are
`synchronized to the reference signal (synchronization clock
`signal). Additionally, the reference signal is supplied (path
`103) along with the data streams to the video session
`manager. The video session manager uses a single oscillator
`source that is phase-locked to the reference signal to modu-
`late all
`the data streams such that
`the streams remain
`
`synchronized. The streams carry timing data via synchro-
`nized data transitions to the set top terminals such that each
`set top terminal is synchronized to a stream then being
`received. Since all streams are synchronized with one
`another, the set-top terminals can seamlessly switch from
`one stream to another without incurring a timing error, i.e.,
`resynchronization is not necessary.
`The following discusses each of the component sub-
`system blocks of the system in detail.
`B. The Server 102
`
`The server 102 is typically a parallel processing computer
`system capable of accepting information requests from the
`video session manager 106, recalling that information from
`memory and generating a plurality of program streams
`containing the information. One such server is the SAR-
`NOFF SERVER computer system manufactured by Sarnoff
`Real Time Corporation of Princeton, N.J. SARNOFF
`SERVER is a trademark of Sarnoff Real Time Corporation.
`The SARNOFF SERVER computer system has an input
`bandwidth of 5.4 Gbps and, at maximum capacity, can serve
`up to 10.8 Gbps of program material. The program infor-
`mation may be stored within the computer system’s disk
`drive array, an off-line storage system such as an optical disk
`library, and/or is available from a real-time program feed
`(digital or analog).
`The server 102 provides a plurality of time division
`multiplexed data streams, e.g., thirty-two, containing the
`information requested by the video session managers to
`service requests for a plurality of subscribers. These signals
`may comply with the MPEG-2 standard for so-called,
`“elementary streams”, “system streams” and “transport
`streams.” These data streams are generally formatted into
`transport packets which comply with the MPEG-2 transport
`protocol or a similar transport protocol. The packetization
`and multiplexing process maybe accomplished within the
`video session manager; however, the packetizing may be
`more efficiently handled by an output subsystem of the
`server or the data can be pre-packetized and stored in the
`data storage devices associated with the server. As such, the
`server provides requested information in a plurality of
`transport streams having the information requested by many
`subscribers packetized and multiplexed into thirty-two inde-
`pendent streams. Each packet carries a TID of a requesting
`set
`top terminal and is presented to the video session
`manager on a particular output port, e.g., one of the 32 ports.
`Additionally, the server provides the high accuracy clock
`signal (reference signal) on path 103.
`Alternatively,
`the plurality of data streams are multi-
`plexed onto an optical cable and a “multidrop” technique is
`used to distribute the streams to the various video session
`
`managers. Specifically, a plurality of “drop lines” connect
`the video session managers to the optical cable (a trunk) and
`the streams are addressed to the appropriate video session
`manager.
`
`To facilitate timing synchronization, the packets used to
`propagate the program information to the set-top terminals
`have a fixed length (i.e., a fixed duration). In essence, the
`
`8
`packetizing process converts the time division multiple
`access (TDMA) streams into packet division multiple access
`(PDMA) streams. Consequently, the packet duration defines
`a fundamental unit of time for the system. As such, the start
`or end of each packet provides an accurate timing signal that
`can be utilized by the set-top terminals for synchronization.
`C. The Video Session Manager 106
`FIG. 2 depicts a block diagram of the video session
`manager 106. As mentioned above, the system generally
`uses multiple video session managers. Each manager pro-
`vides information to up to 16 conventional cable transport
`network nodes (“neighborhood nodes”) having up to 2000
`subscribers each. Each video session manager distributes up
`to 320 different program streams to the nodes.
`The video session manager 106 contains stream distribu-
`tor 200, a digital video modulator (DVM) module 202 (also
`known as a DVM shelf) that contains a plurality of DVMs
`203, a command and control module 216, and an output
`module (coax cross connect 214). The video session man-
`ager 106 also includes a spare DVM module 204 that
`contains a DVM 205 that can be substituted for any one of
`the DVMs 203 using a 1 for n sparing scheme. The stream
`distributor 200 routes the plurality of data streams from the
`server to all DVMs 203. Each DVM has two output ports
`that service one or two neighborhoods. Furthermore, each of
`the output ports may carry either one or two information
`channels. In this manner, the DVM module generates four
`digitally modulated channels that are independently fre-
`quency agile. The output combiner 207 combines the 4
`channels into two pairs of two channels.
`As mentioned with respect to the server description, the
`circuit cards of the video session manager 106 may contain
`a packetizer 206 (shown in phantom) such that the server
`provides time division multiple access system streams and
`the DVM packetizes the information into transport packets
`complying with MPEG-2 or some other transport protocol,
`i.e., a packet division multiple access data stream. However,
`to efficiently process the information streams,
`the server
`generally prov