WO2001086955A1 - Systeme et procede permettant d'utiliser efficacement la largeur de bande pour la diffusion de donnees chronologiques - Google Patents

Systeme et procede permettant d'utiliser efficacement la largeur de bande pour la diffusion de donnees chronologiques Download PDF

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Publication number
WO2001086955A1
WO2001086955A1 PCT/US2001/013876 US0113876W WO0186955A1 WO 2001086955 A1 WO2001086955 A1 WO 2001086955A1 US 0113876 W US0113876 W US 0113876W WO 0186955 A1 WO0186955 A1 WO 0186955A1
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WIPO (PCT)
Prior art keywords
data
fragments
request
transmitted
stream
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PCT/US2001/013876
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English (en)
Inventor
J. Thomas Ngo
Steven E. Saunders
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Interval Research Corporation
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Application filed by Interval Research Corporation filed Critical Interval Research Corporation
Priority to AU2001257432A priority Critical patent/AU2001257432A1/en
Publication of WO2001086955A1 publication Critical patent/WO2001086955A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
    • H04N21/20—Servers specifically adapted for the distribution of content, e.g. VOD servers; Operations thereof
    • H04N21/25—Management operations performed by the server for facilitating the content distribution or administrating data related to end-users or client devices, e.g. end-user or client device authentication, learning user preferences for recommending movies
    • H04N21/266—Channel or content management, e.g. generation and management of keys and entitlement messages in a conditional access system, merging a VOD unicast channel into a multicast channel
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
    • H04N21/20—Servers specifically adapted for the distribution of content, e.g. VOD servers; Operations thereof
    • H04N21/23—Processing of content or additional data; Elementary server operations; Server middleware
    • H04N21/239—Interfacing the upstream path of the transmission network, e.g. prioritizing client content requests
    • H04N21/2393—Interfacing the upstream path of the transmission network, e.g. prioritizing client content requests involving handling client requests
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
    • H04N21/20—Servers specifically adapted for the distribution of content, e.g. VOD servers; Operations thereof
    • H04N21/25—Management operations performed by the server for facilitating the content distribution or administrating data related to end-users or client devices, e.g. end-user or client device authentication, learning user preferences for recommending movies
    • H04N21/266—Channel or content management, e.g. generation and management of keys and entitlement messages in a conditional access system, merging a VOD unicast channel into a multicast channel
    • H04N21/26616—Channel or content management, e.g. generation and management of keys and entitlement messages in a conditional access system, merging a VOD unicast channel into a multicast channel for merging a unicast channel into a multicast channel, e.g. in a VOD application, when a client served by unicast channel catches up a multicast channel to save bandwidth
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
    • H04N21/40—Client devices specifically adapted for the reception of or interaction with content, e.g. set-top-box [STB]; Operations thereof
    • H04N21/47—End-user applications
    • H04N21/472—End-user interface for requesting content, additional data or services; End-user interface for interacting with content, e.g. for content reservation or setting reminders, for requesting event notification, for manipulating displayed content
    • H04N21/47202—End-user interface for requesting content, additional data or services; End-user interface for interacting with content, e.g. for content reservation or setting reminders, for requesting event notification, for manipulating displayed content for requesting content on demand, e.g. video on demand
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
    • H04N21/80—Generation or processing of content or additional data by content creator independently of the distribution process; Content per se
    • H04N21/83—Generation or processing of protective or descriptive data associated with content; Content structuring
    • H04N21/845—Structuring of content, e.g. decomposing content into time segments
    • H04N21/8456—Structuring of content, e.g. decomposing content into time segments by decomposing the content in the time domain, e.g. in time segments
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/16—Analogue secrecy systems; Analogue subscription systems
    • H04N7/173—Analogue secrecy systems; Analogue subscription systems with two-way working, e.g. subscriber sending a programme selection signal
    • H04N7/17309—Transmission or handling of upstream communications
    • H04N7/17336—Handling of requests in head-ends

Definitions

  • the present invention is directed to systems for broadcasting time-ordered data with ininimal commencement delays, such as "on-demand” video services, and more particularly to the efficient utilization of broadcast media bandwidth in such systems.
  • the fragments are transmitted at different respective repetition rates, so that those fragments which occur near the beginning of the original data stream are transmitted more frequently than those which occur later in the data stream.
  • a user enters a command to utilize the data for instance pressing a button on a remote control to view a movie
  • the individual fragments are stored upon receipt at the user's premises, and reassembled into a contiguous stream for viewing.
  • the ordering of the fragments is such that the wait time required to utilize the data is limited to a predetermined maximum, and at least one copy of every fragment becomes available by the time it is needed.
  • the previously cited application describes this technique in the context of a one-way broadcast environment, in which all transmissions are unidirectional, e.g. from a cable system head end or a satellite feed to the end user, as is typical of conventional television broadcast systems.
  • the data for a given presentation is encoded in a periodic manner, and repetitively transmitted.
  • the fragments are grouped into segments of different lengths, and each segment is repetitively transmitted in a corresponding respective substream within the bandwidth allocated to the presentation data.
  • the total amount of the allocated bandwidth is continually dedicated to that data, i.e. other types of data cannot also be transmitted within the allocated bandwidth.
  • the present invention is directed to the broadcast dissemination of time- ordered data in a system which permits users to transmit their requests for data upstream to one or more points along the transmission path between the broadcast system source and the ultimate user.
  • Upstream communications from the user might be accommodated within the broadcast system itself, such as in a two-way cable network, or they might take place by a separate communication system, such as a telephone network.
  • segments of data which are encoded for transmission within respective substreams are selectively transmitted to users in response to specific requests.
  • the first request is serviced by means of data that is transmitted in a conventional, sequential format.
  • Subsequent requests are serviced by transmitting encoded data which is filtered so that those portions of the presentation which have not yet been transmitted in response to earlier requests are not duplicated.
  • a portion of the allocated bandwidth is available to be used for the transmission of other data.
  • the filtering of the data to transmit selected portions of the presentation in response to individual requests is carried out at various locations along the path between the source of the presentation and the end user.
  • the filtering takes place at the transmission source of the broadcast system, so that all users receive the same transmissions and the bandwidth requirements are minimized for the system as a whole. In another embodiment, the filtering takes place at a node located at a point along the transmission path between the source and the users, so that different groups of users can receive different sets of data.
  • each presentation is divided into a leader portion and a remainder portion.
  • the leader portion is transmitted in an unencoded manner over a channel which is shared by all of the leader portions.
  • the remainder of the presentation is transmitted in an encoded manner over a different logical channel, so that it can begin to be viewed as soon as the leader portion has ended.
  • Figure 1 is a block diagram of a television broadcast system in which the present invention can be implemented
  • Figure 2 is an illustration of the segmentation of a presentation for transmission over multiple substreams
  • Figure 3 is an illustration of the transmission of the presentation in response to a first set of requests
  • Figure 4 is an illustration of the transmission of the presentation in response to a second, more closely spaced, set of requests
  • Figure 5 is a graph of the bandwidth that is allocated to an individual user
  • Figure 6 is a graph of the mean bandwidth savings provided by the selective transmission of presentations
  • Figure 7 is a graph of the bandwidth usage for conventional video-on-demand, continuous encoded transmissions and selective encoded transmissions;
  • Figure 8 is an illustration of conventional and encoded transmissions in response to multiple requests;
  • Figure 9 is an illustration of the transmission of overlapping conventional data streams together with encoded data streams
  • FIG. 10 is a block diagram of the basic components for broadcasting presentations in accordance with the present invention.
  • Figure 11 is an illustration of one configuration for a broadcast system
  • Figure 12 is an illustration of a second configuration for a broadcast system.
  • Figure 13 illustrates an example of the transmission of leader data in a shared channel.
  • temporally ordered data refers to any collection of data in which some portion of the data must be received prior to the time that another portion of the data can be utilized.
  • temporally ordered data is a video presentation, wherein the frames of a movie can be received in any order, and stored for subsequent presentation. However, the viewer cannot begin to watch the movie until the first frame has been received.
  • temporally ordered data examples include broadcast media objects such as audio, video or animation in the context of a multi-media presentation.
  • broadcast media objects such as audio, video or animation
  • the invention will be described with particular reference to its application in the context of "on-demand" video services delivered via television networks. It will be appreciated, however, that the invention can be equally applied to other types of temporally ordered data, as well as various communication systems for the broadcast dissemination of such data.
  • a video presentation is divided into a sequence of data fragments and encoded for transmission, in a manner described in detail hereinafter.
  • the encoded fragments are transmitted from a presentation source 10, such as a cable head-end transmission station, to the subscribers' premises in response to requests that are transmitted upstream from the subscribers' premises. These requests might be transmitted via a two-way cable system, or a telephone network, or any other suitable communications system. As discussed in detail hereinafter, the requests may be transmitted to the presentation source 10, or to a node (not shown) which is located between the source 10 and the subscribers' premises.
  • the stream of fragments is received in a suitable set-top converter 12 or other equivalent type of equipment for receiving signals from the source.
  • a decoder 14 within the converter reassembles the fragments into a continuous video stream, and stores them in a suitable frame buffer 16, where they are sequentially presented to the television receivers 18 of subscribers who entered requests.
  • the ordering of the fragments in the encoded stream is such that, regardless of the arbitrary point in time at which a subscriber enters a request to view the presentation, the first fragment of the presentation is available within a period of time ⁇ , and at least one copy of any given fragment becomes available by the time it is needed for viewing in the proper order.
  • the value of ⁇ might be on the order of a few seconds.
  • Figure 2 illustrates the manner in which the fragments are encoded for transmission.
  • the original presentation is divided into fragments of equal length.
  • each fragment can comprise 188 bytes of compressed data.
  • the sequential data fragments are grouped into successive segments of the presentation.
  • the first segment comprises the number of fragments that can be transmitted within the nominal wait time ⁇ that is established for the presentation.
  • Each succeeding segment is longer than the preceding segment by a factor of (1 + ⁇ ), where ⁇ is less than 1/2, and preferably lies in the range 0.04-0.3.
  • the last segment may have a length shorter than ⁇ (l + ⁇ ) k .
  • Each of the segments of the original presentation is transmitted within a respective substream of the bandwidth that is allocated for the encoded transmission.
  • Figure 2 illustrates a presentation of length T which has been divided into 4 segments, which are respectively transmitted within 4 substreams of the allocated bandwidth.
  • Each of the individual substreams can be transmitted in parallel with all of the other substreams. More preferably, however, the substreams are transmitted in a time-division multiplexed manner, to form a complete data stream of encoded data.
  • the total bandwidth required to transmit all of the substreams is identified as ⁇ . This value can be expressed as a factor of the amount of bandwidth required to transmit the presentation in a conventional, i.e., unencoded, manner.
  • FIG 3 illustrates the situation in which two requests for the presentation are spaced by a period of time which is greater than the time required to transmit the longest segment of the presentation.
  • a first copy of each segment is transmitted upon receipt of the first request, Rl .
  • the maximum allocated bandwidth ⁇ is utilized by all of the segment substreams for the duration of the first segment, as indicated by the hatched areas 20.
  • the unused portions of the available bandwidth can be employed to transmit other types of data. For instance, information which is not time-critical, such as program-guide data updates for future presentations, can be downloaded during these periods of available bandwidth capacity and stored at the subscriber's sites.
  • One of the advantageous features of the encoding technique employed within the present invention is the fact that the transmission of segments need not begin with the first fragment of each segment. Rather, as long as one copy of each fragment is transmitted within the period of its associated segment, the transmitted segment can begin with any fragment in that segment. Consequently, if a request is received while segments are being transmitted in response to a previous request, the response to the new request can be initiated immediately at the point where the current transmission is taking place, rather than start at the beginning of the presentation. Hence, the second request can be accommodated within the same allocated bandwidth ⁇ .
  • Figure 4 illustrates an example in which a second request, R2, is received while the transmission of the last few segments of a presentation is taking place in response to a prior request Rl.
  • the first few segments are transmitted in their entirety.
  • those segments whose transmission is still taking place in response to the prior request Rl their transmission continues in the normal fashion, as illustrated by the lightly hatched overlapping areas 24.
  • those portions of the segments which had been transmitted prior to the second request R2 are then retransmitted, as indicated by the more heavily hatched areas 26, so that each subscriber receives at least one complete copy of each segment after making their respective requests.
  • the limiting case occurs when requests for a presentation have a very high frequency, such that they are separated in time by no more than ⁇ . In this case, the segments are continuously repeated in their respective substreams, and none of the allocated bandwidth ⁇ is available for other data. However, when the requests occur less frequently, a portion of the allocated bandwidth becomes available for other types of data.
  • the selective transmission of presentation segments in response to individual requests from users, provides a savings in bandwidth, relative to the continuous transmission of the encoded presentation.
  • the time between adjacent requests can be expressed as fT, where T is the length of the presentation and 0 ⁇ f ⁇ 1.
  • the bandwidth versus time that is required by the selective transmission of the presentation, in response to such an infinite train of requests repeats periodically. Each repeat is equal to the bandwidth versus time that is required to serve an individual subscriber with one complete copy of each segment for some fraction of the movie. The profile of this requirement is illustrated in Figure 5.
  • the bandwidth requirements decrease exponentially over time.
  • the mean saved bandwidth can then be expressed as a function of the time between requests, as illustrated in Figure 6.
  • the abscissa represents the time between requests, expressed as a multiple of the nominal wait time ⁇ .
  • FIG. 7 illustrates the bandwidth usage for three different types of broadcast transmission.
  • Dashed line 30 illustrates the bandwidth usage for continuous transmission of an encoded presentation, as described in Application No. 09/414,514. As can be seen, the bandwidth requirement for continuous transmission remains constant.
  • Line 32 represents the bandwidth usage for the selective transmission of the encoded presentation, in response to individual user requests. As can be seen, the selective transmission provides a significant bandwidth savings, even when the number of simultaneous subscribers is more than 100.
  • These two forms of encoded transmissions are contrasted with the bandwidth requirements for conventional video-on-demand transmission, represented by line 34. In this latter situation, each new request requires the allocation of a dedicated channel to service that request, so that the bandwidth utilization is proportional to the number of concurrent viewers.
  • the later requester can take advantage of fragments that have already been allocated to previous requesters but not yet transmitted.
  • the second request R2 utilizes those fragments in the overlapping areas 24 that are being transmitted in response to the earlier request, Rl. Consequently, in anticipation of future requests, the transmission of each fragment should be delayed to the latest possible moment. Practically speaking, this means that the first request can be serviced by a conventional data stream, in which each of the fragments are transmitted in their original sequence, rather than in an encoded fashion.
  • a second transmission 38 of the presentation begins on a newly allocated channel.
  • This second transmission is encoded as depicted in Figure 2, i.e. segments of fragments are transmitted on respective substreams.
  • the second transmission 38 does not include those portions of the presentation which remain to be sent in response to the earlier request, i.e. that portion of the first transmission 36 which is transmitted subsequent to the second request R2.
  • the transmission 38 that occurs in response to the second request R2 is limited to those segments of the presentation which have already been transmitted in response to the prior request Rl. This limited portion that is transmitted in response to the second request is identified as the "prefix".
  • the second requester receives the remaining portion of the presentation 36 that is being transmitted in a conventional format, and the prefix 38 that is transmitted in the encoded format.
  • the prefix has exponentially decreasing bandwidth requirements, as in the profile of Figure 5.
  • the last segment in the prefix 38 can be a partial segment.
  • additional prefixes are transmitted, as appropriate.
  • the amount of data that is transmitted in each prefix is dependent upon the portion of the presentation that has already been transmitted in the conventional manner. If the second request occurs very soon after the first one, the prefix is quite small, e.g. it may only contain the first few segments of the presentation, and hence require only a few substreams for its transmission. Later requests require a proportionately larger amount of data to be sent in the prefix. In essence, therefore, a portion of the available bandwidth is allocated, or leased, to each copy of the presentation that is requested. A fixed amount of the bandwidth is leased to the first request. The incremental amount of bandwidth that is leased to the second and subsequent requesters depends upon the times at which their requests arrive, relative to the first request. The unleased portion is available for other purposes.
  • the later requester can take advantage of the fragments which are still being transmitted in response to that prior request, as in the situation depicted in Figure 4. Consequently, the maximum bandwidth requirements will remain bounded, in conformance with the graph of Figure 7.
  • the limiting case occurs when the time between requests is no greater than ⁇ . In this case, the total required bandwidth is equal to the amount of bandwidth ⁇ that is allocated to the encoded transmissions, plus the bandwidth required to transmit one conventional version of the presentation.
  • the bandwidth that is employed to transmit the conventional, or sequential, version of the presentation is identified as a first logical channel, and the bandwidth assigned for use by the encoded version of the presentation, i.e. the prefixes, is denoted as a second logical channel.
  • the total bandwidth assigned to both logical channels therefore, is ⁇ + 1.
  • this assigned bandwidth can be readily accommodated within a single analog television channel, e.g. 6MHz, when QAM-64 modulation is employed.
  • the amount of overlap that is permitted between the first and second conventional transmissions is a function of the amount of bandwidth in the second logical channel that is available for the prefixes that derive from the first conventional transmission 36 and those which derive from the second conventional transmission 44.
  • the permissible overlap can be viewed as a function fT, where 0 ⁇ f ⁇ 1.
  • the total amount of available bandwidth must be greater than or equal to ⁇ + logf + ceil(l/f), where log f is a negative number representing the amount of bandwidth that is saved by transmitting prefixes which do not require the full bandwidth ⁇ , and ceil(l/f) is the smallest integer no less than 1/f which represents the number of conventional streams that can be transmitted simultaneously.
  • a second conventional stream can begin to be transmitted at the point at which the bandwidth which is unused by the first conventional stream and all prefixes transmitted up to that point is equal to or greater than the bandwidth that will be required by the second conventional stream and all subsequent prefixes which are based upon the second conventional stream.
  • the bandwidth that is required to satisfy multiple requests for a simultaneous viewing of a presentation can be efficiently utilized by selectively transmitting conventional and encoded versions of the presentation in response to the various requests.
  • the unused portion of the allocated bandwidth can then be employed for other types of data which are not time critical.
  • each presentation is processed in an encoder 50, which determines the fragments that are to be contained within each segment, for transmission in respective substreams, as schematically depicted in Figure 2. If the encoded transmission of a presentation is periodic, the encoded version can be stored after it has been processed, and repetitively transmitted as appropriate. If, however, the encoding is not periodic, the encoding operation is performed on a continual basis.
  • the second step in the process is the allocation of the presentations to various transmission channels, in response to user requests. For example, if the first incoming request is to view Presentation 3, a channel allocator 52 assigns this presentation to the first available transmission channel. In this context, a "transmission channel" can be considered to be the equivalent of an analog television channel. If the next incoming request is for a different presentation, that presentation is assigned to another one of the available transmission channels. Once all of the available channels have been allocated, requests for additional presentations are denied until a channel becomes free, i.e. all transmissions of a previously requested presentation have ended.
  • the third major step in the process is the selective gating, or filtering, of the data that is transmitted on each channel.
  • a conventional stream of data is transmitted on the allocated channel. This can be achieved by decoding the presentation within the filter 54, or by providing the filter with an unencoded version of the presentation from the source.
  • Subsequent requests are serviced by means of encoded transmissions of the segments in their respective substreams.
  • the filter functions to transmit only the necessary portion of each prefix that is required in response to each received request. Hence, it suppresses the transmission of each fragment in a segment after one complete copy of the segment has been sent in response to a request.
  • the filter suppresses the transmission of all later-occurring segments which have not yet been transmitted in the conventional data stream.
  • the filter permits other, non-time-critical data to be transmitted over the channel.
  • the final component of the procedure is the decoder 14, which functions to store and time-shift the fragments in the encoded substreams, so that they appear in sequential order for presentation to the television receiver.
  • Figure 11 a number of different configurations of these four main components are possible.
  • a relatively large amount of bandwidth is available between the presentation source and the subscribers.
  • this configuration might be implemented in a satellite broadcast system having a significant number of transmission channels dedicated to on-demand movies.
  • the functions of the encoder, the channel allocator and the filter are performed at the presentation source 10.
  • the encoded presentations are relayed to the subscriber via a satellite 54.
  • Individual decoders 14 at the subscribers' premises select the desired presentation from one of the available channels, for display.
  • the number of different presentations that can be concurrently viewed by the system's subscribers is equal to the number of channels in the satellite system that are dedicated to the presentations.
  • FIG. 12 A second implementation of the invention is depicted in Figure 12.
  • the presentations are provided to the subscribers by means of a cable television distribution system.
  • the presentations are transmitted from a head end 56 to the subscribers by means of one or more intermediate sites 58 located along the transmission path.
  • An intermediate site can be a hub, a node, a relay station, or the like.
  • node is employed to designate these various types of intermediate sites.
  • Each node serves multiple subscribers, each of whom receives the same data from the node. However, different nodes can transmit different data to their respective subscribers.
  • the transmission media 60 from the head end to the nodes might be optical fiber, whereas the links 62 from the nodes to the individual subscribers' premises might be coaxial cables.
  • the subscribers' requests are transmitted directly to the head end 56. In this case, the functions of the channel allocator and the filter are performed at the head end.
  • the encoding can also be done at the head end if the presentation source, e.g. a server, is located at the head end.
  • the encoding is carried out at a remote presentation source, and the encoded presentations are transmitted to multiple head end stations, for instance by means of a satellite feed.
  • the encoded presentation can be stored at the head end after receiving one copy thereof, or it can be continuously broadcast to the head end, which then selectively passes segments along as they are needed in response to requests.
  • the channel allocator identifies which presentations have been requested by at least one viewer on a node. It assigns each such presentation to a transmission channel on the path 60 to that node. If all of the transmission channels for that node are occupied, further requests for different presentations are temporarily denied, but further requests for the same presentation are fulfilled.
  • the data filter also resides at the head end, and ensures that only one copy of each segment is transmitted to the node for each request.
  • the filtering function can be carried out at the individual nodes, rather than the head end.
  • the requests are transmitted to the nodes, whereupon they are relayed to the head end.
  • the presentations are not transmitted until requests for those presentations are received.
  • the channels are allocated in accordance with the received requests, and the encoded presentations are transmitted to the appropriate nodes.
  • a first presentation might be transmitted over a given channel from the head end to one node, while a different presentation might be transmitted over the same channel from the head end to another node, in response to different requests.
  • the presentations continue to be transmitted, until requests for those presentations are no longer present, i.e. no request has been received within a length of time equal to the largest segment in the presentation.
  • the encoded presentations are selectively filtered, so that one copy of each segment is provided to each requesting subscriber.
  • the encoded presentations are decoded for display.
  • the filtering function at the nodes, rather than the head end, the number of different presentations that can be watched by the subscribers increases, since the subscribers connected to one node are capable of viewing different presentations from those connected to another node.
  • subscribers may not possess decoders which are capable of reorganizing the fragments of an encoded presentation.
  • the function of the decoder is carried out upstream of the subscribers' premises. For instance, it can be implemented at the node, whereupon the presentation is transmitted in the conventional format from the node to the subscribers via the coaxial cable.
  • encoded transmissions can be sent to the head end, via satellite, and multiple decoders at the head end convert the data into a conventional broadcast, for transmission to the end users.
  • each of the functions of encoding the stream of data, allocating transmission channels in response to requests, filtering the fragments that are transmitted, and decoding the data stream can be carried out at a variety of different locations, including the presentation source, the cable system head end, intermediate transmission nodes and the subscribers' premises.
  • the various configurations can be used to advantage to accommodate the bandwidth capabilities of the particular broadcast system in which the invention is implemented, as well as the capabilities within the system for receiving upstream transmissions, operator maintenance requirements, etc.
  • the selective transmission of encoded presentations in response to user requests provides significant bandwidth savings that can be employed to transmit other data.
  • the bandwidth usage associated with a single viewer has an exponentially decreasing profile, with a sharp spike occurring just after the viewer's request is received.
  • the spikes reside in the substreams that carry the shortest segments, which are also the substreams that are least occupied when requests are sparse.
  • This profile suggests that many different presentations can share a fixed-bandwidth channel, by interleaving spikes.
  • each presentation is divided into two portions, an initial leader portion and a remainder portion.
  • the leader portion could comprise, for example, the first few segments of the presentation.
  • a channel of bandwidth ⁇ is used to transmit the remainder portions of each of the encoded presentations, in the manner described previously.
  • An additional channel of bandwidth m ⁇ is allocated for the transmission of the leaders of m presentations .
  • the leaders are transmitted in this additional channel in a shared manner. Requests are answered in order of arrival, with duplicates being eliminated for requests that have not yet been served. When the leader channel is empty, a user's request is answered immediately, by transmitting the leader on that channel, resulting in zero wait time. This situation is illustrated in Figure 13 for the request of a first movie Ml .
  • the remainder of the movie is transmitted in an encoded fashion on channel E l5 and downloaded at the subscriber's premises for viewing once the leader ends.
  • the leader channel is again empty, and so its leader is transmitted immediately at that time, and the remainder of the movie is transmitted in an encoded manner on channel E 2
  • the maximum wait time for the leader is Te ' V ⁇ . This wait time decreases in proportion to the number of movies that are in high demand. For instance, if k ⁇ m movies are popular, the maximum wait time is (k/m) The ⁇ / ⁇ .
  • the spikes associated with the transmissions in the encoded substreams can be reduced.
  • This technique can be combined with other approaches to further reduce the required bandwidth and/or wait time.
  • One such approach is to cache, or store, the initial portion of the leader at the viewer's site.
  • the initial portion of the leader which corresponds to the maximum wait time can be repetitively broadcast.
  • this initial portion is broadcast for a number of movies which are in the highest demand, e.g. ten.
  • Each of these initial portions are stored at the subscriber's premises.
  • the stored portion can be replayed immediately, while the rest of the leader is queued and transmitted over the leader channel, and the remainder of the movie is transmitted in an encoded manner.
  • the user will experience a wait time that is practically zero.
  • caching of the leader can be employed at the source to reduce the effects of the bandwidth spikes.
  • the presentations are stored at the presentation source on magnetic or optical disk media, and retrieved by a server in response to requests.
  • the shortest segments of the most popular presentations can be stored in a fast memory, such as random access memory, to be read therefrom while the remaining segments are retrieved from the disks.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Databases & Information Systems (AREA)
  • Human Computer Interaction (AREA)
  • Two-Way Televisions, Distribution Of Moving Picture Or The Like (AREA)

Abstract

L'invention concerne des segments de données qui sont codées afin d'être transmis à des utilisateurs en réponse à des demandes spécifiques. La première demande peut être satisfaite au moyen de données transmises dans un format séquentiel classique. Pour satisfaire des demandes ultérieures, on transmet des données codées qui sont filtrées de sorte que les parties de la présentation n'ayant pas été transmises en réponse à des demandes précédentes ne sont pas dupliquées. Le filtrage des données visant à transmettre des parties choisies de la présentation en réponse à des demandes individuelles peut avoir lieu en différents endroits sur le chemin allant de la source de la présentation à l'utilisateur final, notamment au niveau de la source du système de diffusion, ou au niveau d'un noeud situé sur un point, sur le chemin de transmission allant de la source aux utilisateurs. Chaque présentation peut se diviser en une partie de tête et en une partie subséquente. En réponse à des demandes de présentations individuelles, la partie de tête est transmise sans codage via un canal partagé par toutes les parties de tête. Le reste de la présentation est transmis avec codage via un canal logique différent, de façon à être visualisé dès que la partie de tête arrive à son terme.
PCT/US2001/013876 2000-05-08 2001-05-01 Systeme et procede permettant d'utiliser efficacement la largeur de bande pour la diffusion de donnees chronologiques WO2001086955A1 (fr)

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AU2001257432A AU2001257432A1 (en) 2000-05-08 2001-05-01 System and method for the efficient utilization of bandwidth in the broadcast dissemination of time-ordered data

Applications Claiming Priority (2)

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US56705300A 2000-05-08 2000-05-08
US09/567,053 2000-05-08

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WO2001086955A1 true WO2001086955A1 (fr) 2001-11-15

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WO2014177523A1 (fr) * 2013-05-02 2014-11-06 Tdf Procédé et dispositif de fourniture d'une partie déjà diffusée d'un flux multimédia, terminal utilisateur, programme d'ordinateur et médium de stockage correspondants

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2014177523A1 (fr) * 2013-05-02 2014-11-06 Tdf Procédé et dispositif de fourniture d'une partie déjà diffusée d'un flux multimédia, terminal utilisateur, programme d'ordinateur et médium de stockage correspondants
FR3005386A1 (fr) * 2013-05-02 2014-11-07 Tdf Procede et dispositif de fourniture d’une partie deja diffusee d’un flux multimedia, terminal utilisateur, programme d’ordinateur et medium de stockage correspondants

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