Electrical computers and digital processing systems: multicomput – Computer-to-computer protocol implementing – Computer-to-computer data transfer regulating
Reexamination Certificate
1999-06-01
2002-12-31
Luu, Le Hien (Department: 2756)
Electrical computers and digital processing systems: multicomput
Computer-to-computer protocol implementing
Computer-to-computer data transfer regulating
C725S101000
Reexamination Certificate
active
06502139
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to a method and system for transmitting a program to a plurality of viewers, permitting flexible, nearly on demand viewing by an unlimited number of concurrent viewers, and, more particularly, to a method and system for transmission that minimizes transmission bandwidth, possibly subject to certain constraints.
Video-On-Demand (VOD) is the on-line version of traditional video-rental services. As with video rental services, each viewer receives a dedicated “copy” of the movie and can view it in a flexible manner, including the ability to pause and resume, rewind, and possibly even fast-forward. With VOD, the “rental” operation is essentially instantaneous, and viewing can begin within seconds of the decision to view.
The “copy” in VOD is a dedicated video stream. This stream is generated by a video server and sent to the viewer over a communication network. An important advantage of VOD over tape rental is the great flexibility in allocation of resources: the maximum number of concurrent viewers is independent of viewing choices, and is limited only by the server's total streaming capacity. The required bandwidth resources, both in the server and in the communication network, are proportional to the number of concurrent viewers.
There are important situations in which a large number of people wish to view the same content during the same period of time, albeit not simultaneously. One example is viewing emergency-preparedness instruction in the hours or days prior to the arrival of a major storm. Another example is a newly released “hot” movie that is advertised heavily. Yet another example is a movie whose viewing is assigned as homework, or even a recorded lecture viewed (individually) in class by the students. These pre-recorded instructions, movies and lectures are examples of programs that are to be viewed by many viewers, concurrently but not necessarily simultaneously.
Although VOD could be used to address such situations, it is both highly desirable and intuitively possible to do better. The desire stems from the fact that even the total (over all programs) number of concurrent viewers may be temporarily much higher than usual, so it would be very costly if not impossible to design the infrastructure (server and communication network) for such peaks. The intuition that something can be done arises from the observation that the many viewers of the “hot” program are viewing the same material concurrently but not simultaneously. The various schemes for doing better than VOD in this situation are called “Near Video On Demand”. The goal of NVOD is to provide an unlimited number of viewers of the same program similar service flexibility to that of VOD at a reasonable cost to the server and communication network. Ideally, this cost is independent of the number of viewers. “Near” is defined to mean commencement of viewing within a reasonable time interval following viewer request, for example one minute in the case of a movie, as well as the ability to pause and resume at any time. Rewind and fast-forward functions are not obligatory.
There are two categories of NVOD systems: open-loop systems and closed-loop systems. In both systems, the viewers are provided with devices, called herein “clients” because of their relationship with the server, that receive program copies transmitted by the server and display those copies to their respective viewers. In open-loop systems there is no feedback from the viewing client to the server, so neither server transmissions nor routing on the network are affected by viewer actions (other than the possible effect on routing due to a viewer joining a multicast group). Open-loop schemes lend themselves most naturally to broadcast-based networks, such as cable television networks, and even to networks that have only one-way communication, which is the common case in satellite-based information-dissemination networks. Closed-loop systems permit some feedback that allows the server to adjust to client requests throughout the viewing period. Note that the terms “play” and “display” are used interchangeably herein, to refer to the displaying of the received program by a client.
Recently, several open-loop NVOD schemes have been proposed. These schemes are based on partitioning the program into several segments, on the assumption that every client has a substantial amount of available storage capacity, for example on a hard disk, which can be used to temporarily store the segments. In such schemes, the server's transmission schedule, and the algorithm used by the client to decide whether or not to record any given transmitted segment, jointly ensure that every segment of the movie is stored in the client's recording medium by its viewing time.
One such scheme is taught by DeBey in U.S. Pat. No. 5,421,031, which is incorporated by reference for all purposes as if fully set forth herein. DeBey's partitioning and scheduling scheme is illustrated in
FIG. 1
, for the case of segments of equal length. The vertical axis of
FIG. 1
is segment number. The horizontal axis of
FIG. 1
is the time at which a given segment is broadcast by the server, with the unit of time, as well as the basic time interval, being the duration of one segment. For each segment, the time during which that segment is broadcast by the server is represented by a double-headed arrow. The first segment is broadcast in every time interval, the second segment is broadcast every second time interval, the third segment is broadcast every third time interval, and in general the n-th segment is broadcast every n-th time interval. Note that all segments are transmitted at the same transmission rate of one segment per time interval. In addition, the transmissions continue throughout the time period during which the viewers are permitted to view the program.
A client that tunes in to the broadcast at the beginning of any time interval receives all the segments promptly enough to display the program with no interruptions. For example, a client that tunes in at the beginning of the seventh time interval, and that actually begins to display the movie to its viewer at the beginning of the eighth time interval, receives and records the seventh copy of the first segment during the seventh time interval, the fourth copy of the second segment during the eighth time interval, the third copy of the third segment during the ninth time interval, the second copy of the fourth segment during the eighth time interval, etc. In this case, the first segment is displayed during the eighth time interval, the second segment is displayed during the ninth time interval, the third segment is displayed during the tenth time interval, the fourth segment is displayed during the eleventh time interval, etc.
DeBey's scheme imposes certain burdens on the server and on the clients. With N segments, the mean transmission bandwidth, in units of segments transmitted per time interval, is approximately ln(N); but the actual transmission bandwidth varies widely. For example, in prime-numbered time intervals after the first time interval, only two segments are broadcast, vs. e.g. six segments during the twelfth time interval. The client must be able to record the received segments fast enough to keep up with the peak aggregate transmission rate. Furthermore, the client must have enough storage capacity to store all recorded segments that are received too soon to play.
There is thus a widely recognized need for, and it would be highly advantageous to have, a NVOD method that imposes less of a burden on the resources available to the server and to the clients.
SUMMARY OF THE INVENTION
According to the present invention there is provided, in a system wherein a server transmits a program having a certain duration, the program being received by at least one client, a method for scheduling the transmission of the program, including the steps of: (a) partitioning the program into a plurality of sequential segments; (b) selecting a transmission ra
Birk Yitzhak
Mondri Ron
Friedman Mark M.
Jaroenchonwanit Bunjob
Luu Le Hien
Technion Research and Development Foundation Ltd.
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