Definitions

• This invention relates generally to data-on-demand systems.
• this invention relates to data transmission scheduling.
• Video-on-demand (VOD) systems are one type of data-on-demand (DOD) system.
• VOD systems video data files are provided by a server or a network of servers to one or more clients on a demand basis.
• a server or a network of servers communicates with clients in a standard hierarchical client-server model.
• a client sends a request to a server for a data file (e.g., a video data file).
• the server sends the requested file to the client.
• a client's request for a data file can be fulfilled by one or more servers.
• the client may have the capability to store any received data file locally in non-volatile memory for later use.
• the standard client-server model requires a two- way communications infrastructure.
• two-way communications requires building new infrastructure because existing cables can only provide one-way communications. Examples of two- way communications infrastructure are hybrid fiber optics coaxial cables (HFC) or all fiber infrastructure. Replacing existing cables is very costly and the resulting services may not be affordable to most users.
• HFC hybrid fiber optics coaxial cables
• the standard client-server model has many limitations when a service provider (e.g., a cable company) attempts to provide VOD services to a large number of clients.
• a service provider e.g., a cable company
• the service provider has to implement a mechanism to continuously listen and fulfill every request from each client within the network; thus, the number of clients who can receive service is dependent on the capacity of such a mechanism.
• One mechanism uses massively-parallel computers having large and fast disk arrays as local servers.
• Even the fastest existing local server can only deliver video data streams to about 1000 to 2000 clients at one time.
• the number of local servers must increase.
• Increasing local servers requires more upper level servers to maintain control of the local servers.
• the present invention provides a DOD broadcast system capable of transmitting one or more data files as a reduced bandwidth client generic sequence of data blocks to a large number of clients simultaneously over a narrow bandwidth, without the need for bi-directional communication.
• the present invention further provides an STB capable of beginning to play a data file broadcast via a client generic format within a short time of the data file being ordered by a client. Further provided is a more bandwidth efficient method of downloading data files by delaying client access time to allow intelligent STBs to load portions of the data files before beginning to play the data files.
• one aspect of the present invention is embodied in a data on demand (DOD) broadcast system for transmitting a plurality of data files, wherein each data file is transmitted as a reduced client generic sequence of data blocks, comprising: a DOD broadcast server for broadcasting a plurality of data files; a transmission medium communicatively coupled with the DOD broadcast server; a plurality of receivers communicatively coupled with the DOD broadcast server via the transmission medium; wherein the DOD broadcast server repeatedly transmits a plurality of data files in a reduced client generic format to the plurality of receivers via the transmission medium; wherein the receivers are operative to request authorization information corresponding to a selected data file; wherein the receivers are further operative to receive the authorization information; and wherein the receivers are further operative to display a portion of the selected data file to a user after a predetermined time period, wherein the predetermined time period enables the receivers to store a portion of the data file before beginning to display the data file.
• DOD data on demand
• Another embodiment of the present invention teaches a data-on-demand (DOD) broadcast method for transmitting a sub-optimal sequence of data blocks comprising the acts of: preparing a sub-optimal data transmission sequence of data blocks, wherein no two adjacent data blocks in the sequence are identical; transmitting a data file consisting of the sequence of data blocks in accordance with the sub-optimal transmission sequence to a plurality of clients in a non client specific manner such that a receiving client may begin to access the data file within a predetermined time period. Furthermore, the predetermined time period has a duration, and wherein the duration is responsive to information included in at least one of the sequence of data blocks.
• DOD data-on-demand
• the act of preparing the sub-optimal data transmission sequence includes the acts of: receiving a data file; specifying a time interval; parsing the data file into a plurality of data blocks based on the time interval such that each data block is displayable during the time interval; determining a required number of time slots to send the data file, wherein each of the time slot has a duration substantially equal to the time interval; allocating to each time slot at least one of the plurality of data blocks.
• a data-on-demand system comprises a first set of channel servers, a central controlling server for controlling the first set of channel servers, a first set of up-converters coupled to the first set of channel servers, a combiner/amplifier coupled to the first set of up-converters, and a combiner/amplifier adapted to transmit data via a transmission medium.
• the data-on-demand system further comprises a channel monitoring module for monitoring the system, a switch matrix, a second set of channel servers, and a second set of up- converters. The channel monitoring module is configured to report to the central controlling server when system failure occurs.
• the central controlling server in response to report from the channel monitoring module, instructs the switch matrix to replace a defective channel server in the first set of channel servers with a channel server in the second set of channel servers and a defective up- converter in the first set of up-converters with an up-converter in the second set of up-converters.
• a method for receiving data files transmitted as a sub-optimal data block sequence comprises the acts of: receiving a user input indicating at least one selected data file; storing at least one of a plurality of data blocks of the sub-optimal data block sequence in a memory location during a predetermined time period; displaying at least a first portion of the data file to a user after the predetermined time period has elapsed; receiving at least one additional data block of the plurality of data blocks of the sub-optimal data block sequence; and displaying at least a second portion of the data file to the user by combining at least one of the stored data blocks with the at least one additional data block.
• set-top-box is not intended to be limited to devices which attach to a television, but may include any device which is capable of receiving broadcast transmissions in accordance with the methods of the present invention including advanced television systems and computers.
• FIGURE 1A illustrates an exemplary DOD system in accordance with an embodiment of the invention
• FIGURE 1 B illustrates an exemplary DOD system in accordance with another embodiment of the invention
• FIGURE 2 illustrates an exemplary channel server in accordance with an embodiment of the invention
• FIGURE 3 illustrates an exemplary set-top box in accordance with an embodiment of the invention
• FIGURE 4 illustrates an exemplary process for generating a scheduling matrix in accordance with an embodiment of the invention
• FIGURE 5 illustrates an exemplary process for generating a sub-optimal scheduling matrix in accordance with one embodiment of the present invention.
• FIGURE 6 illustrates an exemplary STB process for displaying a data file transmitted using a sub-optimal scheduling matrix in accordance with one embodiment of the present invention.
• the present invention provides a DOD broadcast system capable of transmitting one or more data files as a sub-optimal sequence of data blocks to a large number of clients simultaneously over a narrow bandwidth, without the need for bi-directional communication.
• the present invention further provides an STB capable of beginning to play a data file within a short time of the data file being ordered by a client. Further provided is a more bandwidth efficient method of downloading data files by delaying client access time to allow an intelligent STB to load portions of the data files before beginning to play the data files.
• Some potential methods of maximizing transmitted DOD data while minimizing transmission bandwidth include utilizing: constant bandwidth delivery matrices; and decreased idle time matrices. These and other methods are taught by Khoi Hoang's above referenced inventions. While these methods provide client generic DOD services in a time optimal manner, there are other possibilities for providing client generic DOD broadcast services that further reduce required transmission bandwidth in exchange for a delay in access time.
• FIG. 1 A illustrates an exemplary DOD system 100 in accordance with an embodiment of the invention.
• the DOD system 100 provides data files, such as video files, on demand.
• the DOD system 100 is not limited to providing video files on demand but is also capable of providing other data files, for example, game files on demand.
• the DOD system 100 includes a central controlling server 102, a central storage 103, a plurality of channel servers 104a-104n, a plurality of up-converters 106a-106n, and a combiner/amplifier 108.
• the central controlling server 102 controls the channel servers 104.
• the central storage 103 stores data files in digital format.
• data files stored in the central storage 103 are accessible via a standard network interface (e.g., ethernet connection) by any authorized computer, such as the central controller server 102, connected to the network.
• Each channel server 104 is assigned to a channel and is coupled to an up-converter 106.
• the channel servers 104 provide data files that are retrieved from the central storage 103 in accordance with instructions from the central controlling server 102.
• the output of each channel server 104 is a quadrature amplitude modulation (QAM) modulated intermediate frequency (IF) signal having a suitable frequency for the corresponding up-converter 106.
• QAM-modulated IF signals are dependent upon adopted standards.
• the current adopted standard in the United States is the data-over-cable-systems- interface-specification (DOCSIS) standard, which requires an approximately 43.75MHz IF frequency.
• the up-converters 106 convert IF signals received from the channel servers 104 to radio frequency signals (RF signals).
• RF signals which include frequency and bandwidth, are dependent on a desired channel and adopted standards. For example, under the current standard in the United States for a cable television channel 80, the RF signal has a frequency of approximately 559.25MHz and a bandwidth of approximately 6MHz.
• the outputs of the up-converters 106 are applied to the combiner/amplifier 108.
• the combiner/amplifier 108 amplifies, conditions, and combines the received RF signals then outputs the signals out to a transmission medium 110.
• the central controlling server 102 includes a graphics user interface (not shown) to enable a service provider to schedule data delivery by a drag-and-drop operation. Further, the central controlling server 102 authenticates and controls the channel servers 104 to start or stop according to delivery matrices. In an exemplary embodiment, the central controlling server 102 automatically selects a channel and calculates delivery matrices for transmitting data files in the selected channel. The central controlling server 102 provides offline addition, deletion, and update of data file information (e.g., duration, category, rating, and/or brief description). Further, the central controlling server 102 controls the central storage 103 by updating data files and databases stored therein.
• data file information e.g., duration, category, rating, and/or brief description
• an existing cable television system 120 may continue to feed signals into the combiner/amplifier 108 to provide non-DOD services to clients.
• the DOD system 100 in accordance with the invention does not disrupt present cable television services.
• Figure IB illustrates another exemplary embodiment of the DOD system 100 in accordance with the invention.
• the DOD system 100 includes a switch matrix 112, a channel monitoring module 1 14, a set of back-up channel servers 1 16a- 116b, and a set of back-up up-converters 118a- 118b.
• the switch matrix 1 12 is physically located between the up-converters 106 and the combiner/amplifier 108.
• the switch matrix 112 is controlled by the central controlling server 102.
• the channel monitoring module 1 14 comprises a plurality of configured set-top boxes, which simulate potential clients, for monitoring the health of the DOD system 100. Monitoring results are communicated by the channel monitoring module 114 to the central controlling server 102.
• the central controlling server 102 through the switch matrix 112 disengages the malfunctioning component and engages a healthy backup component 116 and/or 1 18 to resume service.
• data files being broadcasted from the DOD system 100 are contained in motion pictures expert group (MPEG) files.
• MPEG motion pictures expert group
• Each MPEG file is dynamically divided into data blocks and sub-blocks mapping to a particular portion of a data file along a time axis. These data blocks and sub-blocks are sent during a pre-determined time in accordance with three- dimensional delivery matrices provided by the central controlling server 102.
• a feedback channel is not necessary for the DOD system 100 to provide DOD services. However, if a feedback channel is available, the feedback channel can be used for other purposes, such as billing or providing Internet services.
• Figure 2 illustrates an exemplary channel server 104 in accordance with an embodiment of the invention.
• the channel server 104 comprises a server controller 202, a CPU 204, a QAM modulator 206, a local memory 208, and a network interface 210.
• the server controller 202 controls the overall operation of the channel server 104 by instructing the CPU 204 to divide data files into blocks (further into sub-blocks and data packets), select data blocks for transmission in accordance with a delivery matrix provided by the central controlling server 102, encode selected data, compress encoded data, then deliver compressed data to the QAM modulator 206.
• the QAM modulator 206 receives data to be transmitted via a bus (i.e., PCI, CPU local bus) or Ethernet connections.
• the QAM modulator 206 may include a downstream QAM modulator, an upstream quadrature amplitude modulation/quadrature phase shift keying (QAM/QPSK) burst demodulator with forward error correction decoder, and/or an upstream tuner.
• the output of the QAM modulator 206 is an IF signals that can be applied directly to an up- converter 106.
• the network interface 210 connects the channel server 104 to other channel servers 104 and to the central controlling server 102 to execute the scheduling and controlling instructions from the central controlling server 102, reporting status back to the central controlling server 102, and receiving data files from the central storage 103. Any data file retrieved from the central storage 103 can be stored in the local memory 208 of the channel server 104 before the data file is processed in accordance with instructions from the server controller 202.
• the channel server 104 may send one or more DOD data streams depending on the bandwidth of a cable channel (e.g., 6, 6.5, or 8MHz), QAM modulation (e.g., QAM 64 or QAM 256, and a compression standard/bit rate of the DOD data stream (i.e., MPEG-1 or MPEG-2).
• a cable channel e.g., 6, 6.5, or 8MHz
• QAM modulation e.g., QAM 64 or QAM 256
• a compression standard/bit rate of the DOD data stream i.e., MPEG-1 or MPEG-2
• FIG. 3 illustrates an exemplary set-top box (STB) 300 in accordance with an embodiment of the invention.
• the STB 300 comprises a QAM demodulator 302, a CPU 304, a conditional access module 306 (e.g., a smart card system), a local memory 308, a buffer memory 309, a STB controller 310, a decoder 312, and a graphics overlay module 314.
• a conditional access module 306 e.g., a smart card system
• a local memory 308 e.g., a smart card system
• a buffer memory 309 e.g., a buffer memory
• decoder 312 e.g., a graphics overlay module
• the STB controller 310 controls the overall operation of the STB 300 by controlling the CPU 302 and the QAM demodulator 302 to select data in response to a client's request, decode selected data, decompress decoded data, reassemble decoded data, store decoded data in the local memory 308 or the buffer memory 309, and deliver stored data to the decoder 312.
• the STB controller 310 controls the overall operation of the STB 300 based on data packet headers in the data packets received from the transmission medium 110.
• the local memory 308 comprises non-volatile memory (e.g., a hard drive) and the buffer memory 309 comprises volatile memory.
• the QAM demodulator 302 comprises transmitter and receiver modules and one or more of the following: privacy encryption/decryption module, forward error correction decoder/encoder, tuner control, downstream and upstream processors, CPU and memory interface circuits.
• the QAM demodulator 302 receives modulated IF signals, samples and demodulates the signals to restore data.
• the conditional access module 306 permits a decoding process when access is granted after authentication and/or when appropriate fees have been charged. Access condition is determined by the service provider.
• Methods of authentication include inserting subscription levels and warning levels directly into the headers of transmitted DOD data.
• the STB 300 reads these subscription levels and compares them to subscription levels stored within the STB 300. If a stored subscription level matches the subscription level transmitted with a DOD service, the client is authorized to receive the service.
• an STB 300 reads a warning level transmitted within a DOD service and displays a message corresponding to the warning level.
• the decoder 312 when access is granted, decodes at least one data block to transform the data block into images displayable on an output screen.
• the decoder 312 supports commands from a subscribing client, such as play, stop, pause, step, rewind, forward, etc.
• the graphics overlay module 314 enhances displayed graphics quality by, for example, providing alpha blending or picture-in-picture capabilities.
• the graphics overlay module 314 can be used for graphics acceleration during game playing mode, for example, when the service provider provides games-on-demand services using the system in accordance with the invention.
• data files are broadcasted to all cable television subscribers, only the DOD subscriber who has a compatible STB 300 will be able to decode and enjoy data-on-demand services.
• permission to obtain data files on demand can be obtained via a smart card system in the conditional access control module 306.
• a smart card may be rechargeable at a local store or vending machine set up by a service provider.
• a flat fee system provides a subscriber unlimited access to all available data files.
• data-on-demand interactive features permit a client to select at any time an available data file.
• the amount of time between when a client presses a select button and the time the selected data file begins playing is referred to as a response time.
• a response time can be determined based on an evaluation of resource allocation and desired quality of service.
• a selected response time determines the duration of a time slot.
• the duration of a time slot (TS) is the time interval for playing a data block at normal speed by a client.
• a data file such as a video file, is divided into a number of data blocks such that each data block can support the playing of the data file for the duration of a time slot.
• the number of data blocks (NUM_OF_BLKS) for each data file can be calculated as follows:
• Estimated_BLK_Size (DataFile Size * TS) / DataFile_Length (1)
• BLK SIZE (Estimated BLK Size + CLUSTER SIZE - lByte) / CLUSTER _SIZE (2)
• BLK_SIZE_BYTES BLK_SIZE * CLUSTER_SIZE (3)
• NUM_OF_BLKS (DataFile_Size + BLK_SIZE_B YTES - 1 Byte)/BLK_SIZE_B YTES (4)
• the Estimated_BLK_Size is an estimated block size (in Bytes); the DataFile_Size is the data file size (in Bytes); TS represents the duration of a time slot (in seconds); DataFileJLength is the duration of the data file (in seconds); BLK SIZE is the number of clusters needed for each data block; CLUSTER _SIZE is the size of a cluster in the local memory 208 for each channel server 104 (e.g., 64KBytes); BLK_SIZE_B TES is a block size in Bytes.
• the number of blocks (NUM_OF_BLKS) is equal to the data file size (in Bytes) plus a data block size in Bytes minus 1, Byte and divided by a data block size in Bytes.
• Equations (1) to (4) illustrate one specific embodiment. A person of skill in the art would recognize that other methods are available to calculate a number of data blocks for a data file. For example, dividing a data file into a number of data blocks is primarily a function of an estimated block size and the cluster size of the local memory 208 of a channel server 104. Thus, the invention should not be limited to the specific embodiment presented above.
• Figure 4 illustrates an exemplary process for generating a scheduling matrix for sending a data file in accordance with an embodiment of the invention.
• this invention uses time division multiplexing (TDM) and frequency division multiplexing (FDM) technology to compress and schedule data delivery at the server side.
• TDM time division multiplexing
• FDM frequency division multiplexing
• a scheduling matrix is generated for each data file.
• each data file is divided into a number of data blocks and the scheduling matrix is generated based on the number of data blocks.
• a scheduling matrix provides a send order for sending data blocks of a data file from a server to clients, such that the data blocks are accessible in sequential order by any client who wishes to access the data file at a random time.
• a number of data blocks (x) for a data file is received.
• a first variable, j is set to zero (step 404).
• a reference array is cleared (step 406). The reference array keeps track of data blocks for internal management purposes.
• j is compared to x (step 408). If j is less than x, a second variable, i, is set to zero (step 412).
• i is compared to x (step 414). If i is less than x, data blocks stored in the column [(i+j) modulo (x)] of a scheduling matrix are written into the reference array (step 418). If the reference array already has such data block(s), do not write a duplicate copy.
• the scheduling matrix and the reference arrays are as follows:
• a look-ahead process can be used to calculate a look-ahead scheduling matrix to send a predetermined number of data blocks of a data file prior to a predicted access time. For example, if a predetermined look-ahead time is the duration of one time slot, for any time slot greater than or equal to time slot number four, data block 4 (blk4) of a data file should be received by a STB 300 at a subscribing client at or before TS3, but blk4 would not be played until TS4.
• the process steps for generating a look-ahead scheduling matrix is substantially similar to the process steps described above for Figure 4 except that the look-ahead scheduling matrix in this embodiment schedules an earlier sending sequence based on a look-ahead time. Assuming a data file is divided into six data blocks, an exemplary sending sequence based on a look-ahead scheduling matrix, having a look-ahead time of the duration of two time slots, can be represented as follows:
• a three-dimensional delivery matrix for sending a set of data files is generated based on the scheduling matrices for each data file of the set of data files.
• a third dimension containing IDs for each data file in the set of data files is generated.
• the three-dimensional delivery matrix is calculated to efficiently utilize available bandwidth in each channel to deliver multiple data streams.
• a convolution method which is well known in the art, is used to generate a three-dimensional delivery matrix to schedule an efficient delivery of a set of data files.
• a convolution method may include the following policies: (1) the total number of data blocks sent in the duration of any time slot (TS) should be kept at a smallest possible number; and (2) if multiple partial solutions are available with respect to policy (1), the preferred solution is the one which has a smallest sum of data blocks by adding the data blocks to be sent during the duration of any reference time slot, data blocks to be sent during the duration of a previous time slot (with respect to the reference time slot), and data blocks to be sent during the duration of a next time slot (with respect to the reference time slot)
• the sending sequence based on a scheduling matrix is as follows
• Option 1 Send video file N at shift 0 TS Total Data Blocks
• Option 2 Send video file N at shift 1 TS Total Data Blocks
• TS5 M0, Ml, M2, M5, NO, Nl, N3
• Option 4 Send video file N at shift 3 TS Total Data Blocks
• TS2 MO, M2, NO, N1 , N2, N5
• TS5 MO, Ml, M2, M5, NO, Nl, N2
• Option 5 Send video file N at shift 4 TS Total Data Blocks
• TS5 M0, Ml, M2, MS, NO, Nl, N3, N4
• options 2, 4, and 6 have the smallest maximum number of data blocks (i.e., 6 data blocks) sent during any time slot.
• the optimal delivery matrix in this exemplary embodiment is option 4 because option 4 has the smallest sum of data blocks of any reference time slot plus data blocks of neighboring time slots (i.e., 16 data blocks).
• the sending sequence of the data file N should be shifted by three time slots.
• a three-dimensional delivery matrix is generated for each channel server 104.
• the DOD system 100 sends data blocks for data files M and N in accordance with the optimal delivery matrix (i.e., shift delivery sequence of data file N by three time slots) in the following manner:
• the STB 300 at client B receives, stores, plays, and rejects data blocks as follows
• the STB 300 of the client C receives, stores, plays, and rejects data blocks as follows
• a client D also selects movie N, the STB 300 at the client D receives, stores, plays, and rejects data blocks as follows
• any combination of clients can at a random time independently select and begin playing any data file provided by the service provider If insufficient bandwidth is available to transmit a given number of data files with the above embodiment, it would be possible to transmit a greater quantity of data with a slight time delay using a sub-optimal transmission schedule as discussed below While the above methods provide client generic DOD services in a time optimal manner, the following processes teach methods for providing client generic DOD broadcast services that further reduce required transmission bandwidth in exchange for a delay in access time
• FIG 5 illustrates an exemplary method at 500 for creating a sub-optimal scheduling matrix
• this invention uses time division multiplexing (TDM) and frequency division multiplexing (FDM) technology to compress and schedule data delivery at the server side
• a sub-optimal scheduling matrix is generated for each data file
• each data file is divided into a number of data blocks and a sub- optimal scheduling matrix is generated based on the number of data blocks
• the sub-optimal scheduling matrix provides a send order for sending data blocks of a data file from a server to clients, such that the data blocks are accessible in sequential order by any client who wishes to access the data file within one time slot of a random starting time
• a first variable, j is set to zero (step 504)
• a reference array is cleared (step 506) The reference array keeps track of data blocks for internal management purposes
• j is compared to x (step 508) If j is less than x, a second variable
• the sub- optimal scheduling matrix and the reference arrays are as follows:
• this exemplary "sub-optimal" scheduling sequence transmits 3 fewer data blocks. This results in a transmission utilizing the exemplary sub-optimal schedule requiring 18.75% less bandwidth.
• This sub-optimal schedule requires a receiving STB to delay displaying a selected data file to a user for a duration of one time slot.
• the sub-optimal schedule of the above embodiment is only one of an infinite number of possible specific scheduling schemes as would be apparent to those skilled in the art. Greater reduction in the bandwidth required to transmit data files may be achieved by using greater delays in STB access time. Examples would include transmissions requiring a delay of 2 or more time slots before a receiving STB could display a selected data file.
• FIG. 6 illustrates an exemplary STB method for receiving "sub-optimal" DOD data transmissions in accordance with one embodiment of the present invention.
• the process 600 starts at a step 602 at which the STB 300 (FIG. 3) receives an electronic guide program (EPG) from the DOD broadcast system 100 (FIG. 1A).
• the EPG program lists all files available from the DOD system 100.
• a user selects a data file listed on the EPG by pressing a purchase button associated with the desired data file.
• the STB 300 (FIG. 3) begins storing data blocks of the selected data file.
• the STB waits a predetermined time period to allow enough data blocks of the selected data file to be stored such that the STB may play the data file without interruption.
• the CPU 304 (FIG 3) is capable of determining how much delay is necessary to assure smooth play of a selected data file. This could be accomplished with various algorithms or by simply including required delay information in a packet header location within the data transmitted from the DOD system 100. In such an embodiment the DOD system varies sub- optimal delivery matrices such that the number of time slots of delay required is dependent on available transmission bandwidth.
• the STB automatically begins playing the selected data file.
• the STB prompts a user to begin display of a selected data file once the delay period is complete.
• a service provider can schedule to send a number of data files (e.g., video files) to channel servers 104 prior to broadcasting.
• the central controlling server 102 calculates and sends to the channel servers 104 three-dimensional delivery matrices (ID, time slot, and data block send order).
• channel servers 104 consult the three-dimensional delivery matrices to send appropriate data blocks in an appropriate order.
• Each data file is divided into data blocks so that a large number of subscribing clients can separately begin viewing a data file continuously and sequentially at a random time.
• a data block size is adjusted to a next higher multiple of a memory cluster size in the local memory 208 of a channel server 104. For example, if a calculated data block length is 720Kbytes according to equation (1) above, then the resulting data block length should be 768Kbytes if the cluster size of the local memory 208 is 64Kbytes.
• data blocks should be further divided into multiples of sub-blocks each having the same size as the cluster size. In this example, the data block has twelve sub-blocks of 64KBytes.
• a sub-block can be further broken down into data packets.
• Each data packet contains a packet header and packet data.
• the packet data length depends on the maximum transfer unit (MTU) of a physical layer where each channel server's CPU sends data to.
• MTU maximum transfer unit
• the total size of the packet header and packet data should be less than the MTU. However, for maximum efficiency, the packet data length should be as long as possible.
• data in a packet header contains information that permits the subscriber client's STB 300 to decode any received data and determine if the data packet belongs to a selected data file (e.g., protocol signature, version, ID, or packet type information).
• the packet header may also contain other information, such as required "sub-optimal" delay period, block/sub- block/packet number, packet length, cyclic redundancy check (CRC) and offset in a sub-block, and/or encoding information.
• CRC cyclic redundancy check
• data packets are sent to the QAM modulator 206 where another header is added to the data packet to generate a QAMmodulated IF output signal.
• the QAM-modulated IF signals are sent to the up-converters 106 to be converted to RF signals suitable for a specific channel (e.g., for CATV channel 80, 559.250MHz and 6MHz bandwidth). For example, if a cable network has high bandwidth (or bit rate), each channel can be used to provide more than one data stream, with each data stream occupying a virtual sub-channel. For example, three MPEG1 data streams can fit into a 6MHz channel using QAM modulation.
• the output of the up-converters 106 is applied to the combiner/amplifier 108, which sends the combined signal to the transmission medium 110.
• BW N x bw
• bw the required bandwidth per data stream.
• three MPEG-1 data streams can be transmitted at the same time by a DOCSIS cable channel having a system bandwidth of 30.3 Mbits/sec. because each MPEG-1 data stream occupies 9 Mbits/sec of the system bandwidth.
• the STB 300 once turned on, continuously receives and updates a program guide stored in the local memory 308 of a STB 300.
• the STB 300 displays data file information including the latest program guide on a TV screen.
• Data file information such as video file information, may include movielD, movie title, description (in multiple languages), category (e.g., action, children), rating (e.g., R, PG13), cable company policy (e.g., price, length of free preview), subscription period, movie poster, and movie preview.
• data file information is sent via a reserved physical channel, such as a channel reserved for firmware update, commercials, and/or emergency information.
• information is sent in a physical channel shared by other data streams.
• a subscribing client can view a list of available data files arranged by categories displayed on a television screen.
• the STB 300 controls its hardware to tune into a corresponding physical channel and/or a virtual sub-channel to start receiving data packets for that data file.
• the STB 300 examines every data packet header, decodes data in the data packets, and determines if a received data packet should be retained. If the STB 300 determines that a data packet should not be retained, the data packet is discarded. Otherwise, the packet data is saved in the local memory 308 for later retrieval or is temporarily stored, in the buffer memory 309 until it is sent to the decoder 312.
• the STB 300 uses a "sliding window" anticipation technique to lock anticipated data blocks in the memory buffer 309 whenever possible. Data blocks are transferred to the decoder 312 directly out of the memory buffer 309 if a hit in an anticipation window occurs. If an anticipation miss occurs, data blocks are read from the local memory 308 into the memory buffer 309 before the data blocks are transferred to the decoder 312 from the memory buffer 309.
• the STB 300 responds to subscribing client's commands via infrared (IR) remote control unit buttons, an IR keyboard, or front panel pushbuttons, including buttons to pause, play in slow motion, rewind, zoom and single step.
• IR infrared
• a subscribing client does not input any action for a predetermined period of time (e.g., scrolling program menu, or selecting a category or movie)
• a scheduled commercial is played automatically.
• the scheduled commercial is automatically stopped when the subscribing client provides an action (e.g., press a button in a remote control unit).
• the STB 300 can automatically insert commercials while a video is being played.
• the service provider e.g., a cable company
• the service provider can set up a pricing policy that dictates how frequently commercials should interrupt the video being played. If an emergency information bit is found in a data packet header, the STB 300 pauses any data receiving operation and controls its hardware to tune into the channel reserved for receiving data file information to obtain and decode any emergency information to be displayed on an output screen. In an exemplary embodiment, when the STB 300 is idled, it is tuned to the channel reserved for receiving data file information and is always ready to receive and display any emergency information without delay.

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