Electrical computers and digital processing systems: multicomput – Distributed data processing – Processing agent
Patent
1997-09-02
2000-07-04
Asta, Frank J.
Electrical computers and digital processing systems: multicomput
Distributed data processing
Processing agent
709243, 709231, 370 82, 370 8515, H04L 1516
Patent
active
060852216
DESCRIPTION:
BRIEF SUMMARY
This invention concerns distribution of multimedia files by file servers over an arbitrary network for information transfer, like a wide area network (WAN), for example the Broadband-ISDN or the Internet, or like a local area network (LAN). It is related to all time critical files which are coded with a variable amount of data over time, for instance, video files like movies, audio presentations, or teleconference presentations. In particular, the invention is directed to video-on-demand (VOD) services, as being envisaged for interactive television where the transmission quality is to remain constant despite given fluctuations in the amount of coded data, and where a continuous play-back of a demanded video is provided.
Known video file servers in such an environment serve as providers to play back compressed digital videos to clients over a telecommunication network. Those clients, on their side, need special decoders to convert the digital video signal in a television signal. These decoders comprise further a decoder buffer, and are usually implemented in a so-called Set-Top-Box. The videos are transmitted as frames of a given time duration. Commonly a predetermined constant bitrate for data file transfer is provided in order to achieve a simple management of network resources (FIG. 2). As the compression ratio and therefore the size of a compressed frame of a video depends on the respective scene content, a compressed video comprises inherently a variable bitrate. For these reasons, file servers delivering movies are confronted with the problem of an extreme time dependent variation of information amount which has to be transferred from the server to the user at a given time.
A conventional multimedia data server is disclosed in U.S. patent application Ser. No. 288,525 (Docketno. RO9-93-060) filed on Aug. 10, 1994, by the present applicant. This server comprises a direct access storage device (DASD), a plurality of data buffers, each of said buffers corresponding to a respective time interval associated with a multimedia presentation, and a mass storage device for storing the multimedia presentation data. A data bus connects the mass storage with the plurality of data buffers, wherein a bus switch is provided being operated by a controller.
A Set-Top-Box for the receiving side of a multimedia communication system according to the prior art is disclosed in U.S. patent application Ser. No. 473,315 (Docket no. RO9-95-042) filed on Jun. 7, 1995, which is also assigned to the present applicant. This device effectuates local reception and processing of multimedia programs received from a remote multimedia file server. The local Set-Top-Box control system includes a DASD adapted to buffer a predetermined number of compressed program segments received from a multimedia file server. In particular, that invention is directed to a novel formatting methodology which provides concurrent presentation and buffering of program segments received from the server for on-demand viewing of a selected multimedia program.
Further for the transmission of compressed video files over a digital telecommunication link, for instance one operating in the known Asynchronous Transfer Mode (ATM), two compression modes are currently considered: constant bitrate and variable bitrate. These modes are illustrated in FIG. 2. A respective approach to achieve a constant bitrate, is to use a special compression mechanism with a so-called "closed-loop control" in the encoder that adjusts the picture quality as a function of the encoder buffer fill level. The respective variable quantization in the compression process leads to a variable quality. The quality decreases in scenes with high image complexity or heavy motion. In contrast, a compression process with constant quantization, of course, avoids the problem of changing quality, but it produces a video file with variable bitrate over time which is difficult to manage in networks with respect to the bursty traffic due to the fluctuating rate as a function of the scene contents.
The pre-cited
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Asta Frank J.
Dillon Andrew J.
International Business Machines - Corporation
Musgrove Jack V.
Vu Thong
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