Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via frequency channels
Reexamination Certificate
1998-09-03
2001-10-02
Vu, Huy D. (Department: 2733)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via frequency channels
C370S395430
Reexamination Certificate
active
06298071
ABSTRACT:
The invention relates to information distribution systems generally and, more particularly, the invention relates to a method and apparatus for adapting the distribution of stored information streams in response to disk bandwidth availability and/or distribution channel bandwidth availability.
BACKGROUND OF THE DISCLOSURE
In several communications systems the data to be transmitted is compressed so that the available bandwidth is used more efficiently. For example, the Moving Pictures Experts Group (MPEG) has promulgated several standards relating to digital data delivery systems. The first, known as MPEG-1 refers to ISO/IEC standards 11172 and is incorporated herein by reference. The second, known as MPEG-2, refers to ISO/IEC standards 13818 and is incorporated herein by reference. A compressed digital video system is described in the Advanced Television Systems Committee (ATSC) digital television standard document A/53, and is incorporated herein by reference.
In information distribution applications, such as video on demand (VOD) and other applications in which a plurality of subscribers receive respective information stream(s), it is desirable to use variable bit rate (VBR) streams so that video image quality and link (network) utilization may be maximized. With VBR streams, the bit rate fluctuates with the complexity of the video. That is, more bits are given to complex frames and fewer bits are given to the easy to code frames. However, “serving” such VBR information streams provides a substantial challenge when implementing a cost effective video server. The primary difficulty is determining is what happens when the demand for bandwidth exceeds the channel capacity.
VBR MPEG is currently used in one or more satellite television systems. Such systems typically encode a set of channels (i.e., audio-visual programs) together, using a statistical multiplexer that drives the rate controller of each channel encoder. All the decisions about how to allocated the available bits are decided when the video is being encoded, just before transmission.
Unfortunately, the above-described encoding-level approach to bandwidth management does not work within the context of, e.g., a video server that typically delivers pre-encoded content, and typically has no control over which streams need to be sent over a given link. Thus, such video servers typically serve VBR streams by reserving disk and link bandwidth based on a maximum bit rate that the served stream will require. While this technique works well, the additional video quality is provided at the expense of underutilized link bandwidth. Moreover, in systems where multiple subscribers require information stored in a single mass storage unit (or array of mass storage devices), disk bandwidth (i.e., the maximum amount of data that may be retrieved in a given time period) may be exceeded by the aggregated bandwidth demands of the subscribers, especially where VBR streams are retrieved from the disk.
Therefore, it is seen to be desirable to provide a method and apparatus for providing high quality information streams while managing both link and disk bandwidth utilization within the context of a multiple subscriber or user information distribution system.
SUMMARY OF THE INVENTION
The invention is a method and apparatus for managing both link and disk bandwidth utilization within the context of a multiple subscriber or user information distribution system by selectively providing variable bitrate and constant low bitrate information streams to one or more subscribers.
Specifically, in an information distribution system comprising an information server providing information to a plurality of subscribers via a communications link, a method according to the invention for managing bandwidth utilization comprises the steps of: monitoring an indicium of bandwidth utilization within the information distribution system; providing, via the communications link and in response to the indicium of bandwidth utilization indicating that an overutilization condition does not exist, a first variable bitrate information stream to at least one of the plurality of subscribers, the first variable bitrate information stream having associated with it a bitrate that may vary between a nominal first lower bitrate and a nominal first upper bitrate; and providing, via the communications link and in response to the indicium of bandwidth utilization indicating that an overutilization condition does exist, a second variable bitrate information stream to at least one of the plurality of subscribers, the second variable bitrate information stream having associated with it a bitrate that may vary between a nominal second lower bitrate and a nominal second upper bitrate, the nominal second lower bitrate being and the nominal second upper bitrate being less than the nominal first upper bitrate.
The above-mention indicium of bandwidth utilization comprises one of a communications link bandwidth utilization indicium and a storage device access bandwidth utilization indicium, the storage device being used to store the first and second variable bitrate information streams.
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Lerman Jesse S.
Taylor Clement G.
Boakye Alexander
DIVA Systems Corporation
Thomason Moser & Patterson LLP
Vu Huy D.
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