Efficient memory management in VOD disk array servers usingPer-Storage-Device buffering

We present a buffering technique that reduces video-on-demand server memory requirements in more than one order of magnitude. This technique, Per-Storage-Device Buffering (PSDB), is based on the allocation of a fixed number of buffers per storage device, as opposed to existing solutions based on per-stream buffering allocation. The combination of this technique with disk array servers is studied in detail, as well as the influence of Variable Bit Streams. We also present an interleaved data placement strategy, Constant Time Length Declustering, that results in optimal performance in the service of VBR streams. PSDB is evaluated by extensive simulation of a disk array server model that incorporates a simulation based admission test.This research was supported in part by the National R&D Program of Spain, Project Number TIC97-0438.Publicad

Minimizing buffer requirements in video-on-demand servers

23rd Euromicro Conference EUROMICRO 97: 'New Frontiers of Information Technology', Budapest, Hungary, 1-4 Sept 1997Memory management is a key issue when designing cost effective video on demand servers. State of the art techniques, like double buffering, allocate buffers in a per stream basis and require huge amounts of memory. We propose a buffering policy, namely Single Pair of Buffers, that dramatically reduces server memory requirements by reserving a pair of buffers per storage device. By considering in detail disk and network interaction, we have also identified the particular conditions under which this policy can be successfully applied to engineer video on demand servers. Reduction factors of two orders of magnitude compared to the double buffering approach can be obtained. Current disk and network parameters make this technique feasible.Publicad

Distributed multimedia systems

A distributed multimedia system (DMS) is an integrated communication, computing, and information system that enables the processing, management, delivery, and presentation of synchronized multimedia information with quality-of-service guarantees. Multimedia information may include discrete media data, such as text, data, and images, and continuous media data, such as video and audio. Such a system enhances human communications by exploiting both visual and aural senses and provides the ultimate flexibility in work and entertainment, allowing one to collaborate with remote participants, view movies on demand, access on-line digital libraries from the desktop, and so forth. In this paper, we present a technical survey of a DMS. We give an overview of distributed multimedia systems, examine the fundamental concept of digital media, identify the applications, and survey the important enabling technologies.published_or_final_versio

Evaluation of Tradeoffs in Resource Management Techniques for Multimedia Storage Servers

Many modern applications can benefit from sharing of resources such as network bandwidth, disk bandwidth, and so on. In addition, many information systems store (or would like to store) data that can be of use to many different classes of applications, e.g., digital libraries type systems. Part of the difficulty in efficient resource management of such systems can then occur when these applications have vastly different performance and quality-of-service (QoS) requirements as well as resource demand characteristics. In this work we present a performance study of a multimedia storage system which serves multiple types of workloads, specifically a mixture of real-time and non-real-time workloads, by allowing sharing of resources among these different workloads while satisfying their performance requirements and QoS constraints. The broad aim of this work is to examine the issues and tradeoffs associated with mixing multiple workloads on the same server to explore the possibility of maintaining reasonable performance and QoS requirements without having to partition the resources. The main contribution of this work is the exposition of the tradeoffs involved in resource management in such systems. Although many different resources can be considered, here we concentrate mostly on the I/O bandwidth resource. The performance metrics of interest are the mean and variance of the response time for the non-real-time applications and the probability of missing a deadline for the real-time applications. The increased use of buffer space resources is also considered as a tradeoff for improvements in the above stated performance metrics, i.e., response time and probability of missing deadlines. (Also cross-referenced as UMIACS-TR-98-30

Platten-Scheduling und stochastische Service-Garantien für multimediale Daten-Server

In dieser Arbeit werden neuartige Algorithmen für das Platten-Scheduling in multimedialen Daten-Servern vorgestellt und ein stochastisches Modell zur Vorhersage der vom Server garantierbaren Service-Qualität entwickelt. Angenommen wird, daß die Speicherung der multimedialen Daten auf den Platten eines Disk-Arrays gemischt erfolgt. Dies bedeutet, daß sowohl kontinuierliche Daten (Audio, Video) als auch diskrete Daten (Text, Bild, Graphik) gemeinsam auf einer Platte abgelegt werden. Bedingt durch diese gemischte Datenhaltung muß jede Magnetplatte Zugriffe auf kontinuierliche und diskrete Daten verarbeiten können. Die Auswirkungen verschiedener Scheduling-Algorithmen auf die Service-Qualität beim Datenzugriff auf kontinuierliche und diskrete Daten werden experimentell evaluiert. Die Service- Qualität für kontinuierliche Daten ist hierbei durch die Störungsrate bestimmt, d.h. durch die Haüfigkeit, mit der der Server zeitweilig die U¨ bertragung des Datenstromes zum Client unterbrechen muß. Die Service-Qualität für diskrete Daten wird durch die Antwortzeit festgelegt. Grundlage für die Vorhersage der Service-Qualität bildet die stochastische Modellierung des Daten-Servers. Zu diesem Zweck wird die Verteilungsfunktion für die Zeitdauer analysiert, die für eine Menge von Plattenzugriffen benötigt wird. Hierauf aufbauend läßt sich dieWahrscheinlichkeit bestimmen, mit der eine festgelegte Störungsrate bzw. eine festgelegte Antwortzeitschranke überschritten wird. Für letzteres wird ein M/G/1-Warteschlangenmodell entwickelt, das die Verteilungsfunktion der Antwortzeit in Form der Laplace-Transformierten berechnet. Die Vorhersagen des stochastischen Modells bilden die Basis für die Konfiguration des Disk- Arrays und für die Zulassungkontrolle, mit der der Server die vereinbarte Service-Qualität garantieren kann.This thesis presents new methods for disk scheduling in multimedia servers and derives a stochastic model to predict the quality-of-service that the server can guarantee. It is assumed that all data, i.e. continuous data (audio/video) and discrete data (text/indexes/images), resides for efficiency reasons on a shared disk-array. Thus, accesses to this data induce a mixed workload on each disk. The impact of different disk scheduling policies on the quality-of-service for both continuous and discrete data is studied, and a framework for describing various policies in terms of a few parameters is developed. The quality-of-service for continuous data is determined by the error rate, i.e. the frequency of the server temporarily suspending the delivery of data to the client. The quality-of-service for discrete data is given by the response time for discrete data requests. A stochastic model is developed based on deriving the distribution function of the service time for batched disk service under a multi-user load. Using this result it is possible to bound the tail probabilities of the error rate and the response time. The latter can be obtained using an M/G/1 queueing model that derives the Laplace transform of the response time distribution. The results from the stochastic model provide the basis for configuring the disk-array and exerting an admission control such that the server can guarantee its quality-of-service

Research & Technology Report Goddard Space Flight Center

The main theme of this edition of the annual Research and Technology Report is Mission Operations and Data Systems. Shifting from centralized to distributed mission operations, and from human interactive operations to highly automated operations is reported. The following aspects are addressed: Mission planning and operations; TDRSS, Positioning Systems, and orbit determination; hardware and software associated with Ground System and Networks; data processing and analysis; and World Wide Web. Flight projects are described along with the achievements in space sciences and earth sciences. Spacecraft subsystems, cryogenic developments, and new tools and capabilities are also discussed

Research and Technology Report. Goddard Space Flight Center

This issue of Goddard Space Flight Center's annual report highlights the importance of mission operations and data systems covering mission planning and operations; TDRSS, positioning systems, and orbit determination; ground system and networks, hardware and software; data processing and analysis; and World Wide Web use. The report also includes flight projects, space sciences, Earth system science, and engineering and materials

Multiple Media Correlation: Theory and Applications

This thesis introduces multiple media correlation, a new technology for the automatic alignment of multiple media objects such as text, audio, and video. This research began with the question: what can be learned when multiple multimedia components are analyzed simultaneously? Most ongoing research in computational multimedia has focused on queries, indexing, and retrieval within a single media type. Video is compressed and searched independently of audio, text is indexed without regard to temporal relationships it may have to other media data. Multiple media correlation provides a framework for locating and exploiting correlations between multiple, potentially heterogeneous, media streams. The goal is computed synchronization, the determination of temporal and spatial alignments that optimize a correlation function and indicate commonality and synchronization between media objects. The model also provides a basis for comparison of media in unrelated domains. There are many real-world applications for this technology, including speaker localization, musical score alignment, and degraded media realignment. Two applications, text-to-speech alignment and parallel text alignment, are described in detail with experimental validation. Text-to-speech alignment computes the alignment between a textual transcript and speech-based audio. The presented solutions are effective for a wide variety of content and are useful not only for retrieval of content, but in support of automatic captioning of movies and video. Parallel text alignment provides a tool for the comparison of alternative translations of the same document that is particularly useful to the classics scholar interested in comparing translation techniques or styles. The results presented in this thesis include (a) new media models more useful in analysis applications, (b) a theoretical model for multiple media correlation, (c) two practical application solutions that have wide-spread applicability, and (d) Xtrieve, a multimedia database retrieval system that demonstrates this new technology and demonstrates application of multiple media correlation to information retrieval. This thesis demonstrates that computed alignment of media objects is practical and can provide immediate solutions to many information retrieval and content presentation problems. It also introduces a new area for research in media data analysis