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1.
For admission control in real-time multimedia systems, buffer space, disk bandwidth and network bandwidth must be considered.
The CBR-based mechanisms do not use system resources effectively, since media data is usually encoded with VBR compression
techniques. We propose an admission control mechanism based on a VBR data model that has a dynamic period length. In our mechanism,
the period can be adaptively changed to maximize the performance, considering both disk bandwidth and buffer space. To compare
the performance, extensive simulations are conducted on RR, SCAN, and GSS schemes which have the dynamic period length and
the static period length. 相似文献
2.
An optimal bandwidth allocation strategy for the delivery of compressed prerecorded video 总被引:1,自引:0,他引:1
The transportation of prerecorded, compressed video data without loss of picture quality requires the network and video
servers to support large fluctuations in bandwidth requirements. Fully utilizing a client-side buffer for smoothing bandwidth
requirements can limit the fluctuations in bandwidth required from the underlying network and the video-on-demand servers.
This paper shows that, for a fixed-size buffer constraint, the critical bandwidth allocation technique results in plans
for continuous playback of stored video that have (1) the minimum number of bandwidth increases, (2) the smallest peak bandwidth
requirements, and (3) the largest minimum bandwidth requirements. In addition, this paper introduces an optimal bandwidth allocation algorithm which, in addition to the three critical bandwidth allocation properties, minimizes the total number of bandwidth
changes necessary for continuous playback. A comparison between the optimal bandwidth allocation algorithm and other critical
bandwidth-based algorithms using 17 full-length movie videos and 3 seminar videos is also presented. 相似文献
3.
A video-on-demand (VOD) server needs to store hundreds of movie titles and to support thousands of concurrent accesses.
This, technically and economically, imposes a great challenge on the design of the disk storage subsystem of a VOD server.
Due to different demands for different movie titles, the numbers of concurrent accesses to each movie can differ a lot. We
define access profile as the number of concurrent accesses to each movie title that should be supported by a VOD server.
The access profile is derived based on the popularity of each movie title and thus serves as a major design goal for the
disk storage subsystem. Since some popular (hot) movie titles may be concurrently accessed by hundreds of users and a current
high-end magnetic disk array (disk) can only support tens of concurrent accesses, it is necessary to replicate and/or stripe
the hot movie files over multiple disk arrays. The consequence of replication and striping of hot movie titles is the potential
increase on the required number of disk arrays. Therefore, how to replicate, stripe, and place the movie files over a minimum
number of magnetic disk arrays such that a given access profile can be supported is an important problem. In this paper,
we formulate the problem of the video file allocation over disk arrays, demonstrate that it is a NP-hard problem, and present
some heuristic algorithms to find the near-optimal solutions. The result of this study can be applied to the design of the
storage subsystem of a VOD server to economically minimize the cost or to maximize the utilization of disk arrays. 相似文献
4.
The paper investigates efficient bandwidth allocation schemes for the transmission of MPEG-2 video traffic on high-speed
networks. To this end we performed an extensive analysis of the traffic generated by an MPEG-2 encoder. Specifically, we encoded
“The Sheltering Sky” movie according to the MPEG-2 standard. By the analysis of the generated traffic it results that a constant-quality
transmission can be performed with a poor bandwidth utilization. In the paper we identified that the low bandwidth utilization
is caused by rare high-rate periods in the codec bitstream. Hence, we identified the source scalability as a promising approach
to achieve a “quasi-constant” quality transmission and an efficient bandwidth utilization. The effectiveness of this approach
is evaluated in the paper via simulation. Specifically, by defining a Markovian model for an MPEG-2 scalable source we performed
a set of simulation experiments which indicate that the source scalability approach significantly increases the utilization,
while maintaining the quality of the video signal at the highest value for most of the time, e.g., a 50% of the network utilization
with the highest quality for the 99.7% of the time. 相似文献
5.
Excessive buffer requirement to handle continuous-media playbacks is an impediment to cost- effective provisioning for on-line
video retrieval. Given the skewed distribution of video popularity, it is expected that often there are concurrent playbacks
of the same video file within a short time interval. This creates an opportunity to batch multiple requests and to service
them with a single stream from the disk without violating the on-demand constraint. However, there is a need to keep data
in memory between successive uses to do this. This leads to a buffer space trade-off between servicing a request in memory mode vs. servicing it in disk-mode. In this work, we develop a novel algorithm to minimize the buffer requirement to support a set of concurrent playbacks.
One of the beauties of the proposed scheme is that it enables the server to dynamically adapt to the changing workload while
minimizing the total buffer space requirement. Our algorithm makes a significant contribution in decreasing the total buffer
requirement, especially when the user access pattern is biased in favor of a small set of files. The idea of the proposed
scheme is modeled in detail using an analytical formulation, and optimality of the algorithm is proved. An analytical framework
is developed so that the proposed scheme can be used in combination with various existing disk-scheduling strategies. Our
simulation results confirm that under certain circumstances, it is much more resource efficient to support some of the playbacks
in memory mode and subsequently the proposed scheme enables the server to minimize the overall buffer space requirement. 相似文献
6.
Adaptive piggybacking: a novel technique for data sharing in video-on-demand storage servers 总被引:17,自引:0,他引:17
Recent technology advances have made multimedia on-demand services, such as home entertainment and home-shopping, important
to the consumer market. One of the most challenging aspects of this type of service is providing access either instantaneously
or within a small and reasonable latency upon request. We consider improvements in the performance of multimedia storage servers
through data sharing between requests for popular objects, assuming that the I/O bandwidth is the critical resource in the system. We discuss a novel approach to data sharing,
termed adaptive piggybacking, which can be used to reduce the aggregate I/O demand on the multimedia storage server and thus
reduce latency for servicing new requests. 相似文献
7.
In this paper, we propose and study a dynamic approach to schedule real-time requests in a video-on-demand (VOD) server.
Providing quality of service in such servers requires uninterrupted and on-time retrieval of motion video data. VOD services
and multimedia applications further require access to the storage devices to be shared among multiple concurrent streams.
Most of the previous VOD scheduling approaches use limited run-time,0 information and thus cannot exploit the potential capacity
of the system fully. Our approach improves throughput by making use of run-time information to relax admission control. It
maintains excellent quality of service under varying playout rates by observing deadlines and by reallocating resources to
guarantee continuous service. It also reduces start-up latency by beginning service as soon as it is detected that deadlines
of all real-time requests will be met. We establish safe conditions for greedy admission, dynamic control of disk read sizes,
fast initial service, and sporadic services. We conduct thorough simulations over a wide range of buffer capacities, load
settings, and over varying playout rates to demonstrate the significant improvements in quality of service, throughput and
start-up latency of our approach relative to a static approach. 相似文献
8.
We present efficient schemes for scheduling the delivery of variable-bit-rate MPEG-compressed video with stringent quality-of-service
(QoS) requirements. Video scheduling is being used to improve bandwidth allocation at a video server that uses statistical
multiplexing to aggregate video streams prior to transporting them over a network. A video stream is modeled using a traffic
envelope that provides a deterministic time-varying bound on the bit rate. Because of the periodicity in which frame types
in an MPEG stream are typically generated, a simple traffic envelope can be constructed using only five parameters. Using
the traffic-envelope model, we show that video sources can be statistically multiplexed with an effective bandwidth that is often less than the source peak rate. Bandwidth gain is achieved without sacrificing the stringency of the requested
QoS. The effective bandwidth depends on the arrangement of the multiplexed streams, which is a measure of the lag between the GOP periods of various streams. For homogeneous streams,
we give an optimal scheduling scheme for video sources at a video-on-demand server that results in the minimum effective bandwidth.
For heterogeneous sources, a sub-optimal scheduling scheme is given, which achieves acceptable bandwidth gain. Numerical examples
based on traces of MPEG-coded movies are used to demonstrate the effectiveness of our schemes. 相似文献
9.
Operating system issues for continuous media 总被引:1,自引:0,他引:1
Henning Schulzrinne 《Multimedia Systems》1996,4(5):269-280
Continuous media such as audio and video pose new challenges to all parts of multipurpose operating systems. We discuss issues
related to CPU scheduling, memory allocation, system support and application environments and summarize some of the solutions
proposed in the literature. 相似文献
10.
This paper presents a new data placement scheme for continuous-media playback via a scalable storage system. Multimedia contents
are segmented into data blocks for the purpose of being stored, retrieved, and manipulated. If these data blocks belong to
some continuous media, then they must be handled in a timely manner, for example, being retrieved before some deadline. One
of the main challenges in implementing the above system is the simultaneous retrieval of a great number of different media
streams from a very large storage system. The proposed scheme efficiently reduces the seeking delay by a very simple placement
method and a retrieval scheduler. Thus, both the storage capacity and the number of concurrent accesses to the storage are
scalable. The performance of the proposed scheme is evaluated through a simple analytical model and a practical prototype
implementation. 相似文献
11.
Multimedia data, especially continuous media including video and audio objects, represent a rich and natural stimulus for
humans, but require large amount of storage capacity and real-time processing. In this paper, we describe how to organize
video data efficiently on multiple disks in order to support arbitrary-rate playback requested by different users independently.
Our approach is to segment and decluster video objects and to place the segments in multiple disks using a restricted round-robin
scheme, called prime round-robin (PRR). Its placement scheme provides uniform load balance of disks for arbitrary retrieval rate as well as normal playback,
since it eliminates hot spots. Moreover, it does not require any additional disk bandwidth to support VCR-like operations
such as fast-forward and rewind. We have studied the various effects of placement and retrieval schemes in a storage server
by simulation. The results show that PRR offers even disk accesses, and the failure in reading segment by deadline occurs
only at the beginning of new operations. In addition, the number of users admitted is not decreased, regardless of arbitrary-rate
playback requests. 相似文献
12.
We present a novel technique, called 2-Phase Service Model, for streaming videos to home users in a limited-bandwidth environment. This scheme first delivers some number of non-adjacent
data fragments to the client in Phase 1. The missing fragments are then transmitted in Phase 2 as the client is playing back
the video. This approach offers many benefits. The isochronous bandwidth required for Phase 2 can be controlled within the
capability of the transport medium. The data fragments received during Phase 1 can be used to provide an excellent preview
of the video. They can also be used to facilitate VCR-style operations such as fast-forward and fast-reverse. Systems designed
based on this method are less expensive because the fast-forward and fast-reverse versions of the video files are no longer
needed. Eliminating these files also improves system performance because mapping between the regular files and their fast-forward
and fast-reverse versions is no longer part of the VCR operations. Furthermore, since each client machine handles its own
VCR-style interaction, this technique is very scalable. We provide simulation results to show that 2-Phase Service Model is
able to handle VCR functions efficiently. We also implement a video player called {\em FRVplayer}. With this prototype, we
are able to judge that the visual quality of the previews and VCR-style operations is excellent. These features are essential
to many important applications. We discuss the application of FRVplayer in the design of a video management system, called
VideoCenter. This system is intended for Internet applications such as digital video libraries. 相似文献
13.
The major drawback of the existing cluster placement scheme is the long response time caused by admission control if the
number of clusters and the number of users are large. A circular skip-cluster placement scheme is proposed to reduce the size
of the data buffer as well as the system response time. Furthermore, the popularity of each video is different in the real
world. We propose a new popularity-based data allocation scheme to allocate data units within a cluster such that the corresponding
data units of these popular videos are stored in those cylinders at one end of each cluster. Due to a higher spatial locality
within these hot cylinders, some data units requested by the users are stored in the same cylinder such that one seek operation,
one rotation, and one transfer operation are required to retrieve these data units. Therefore, the time required to retrieve
data for these requests can be reduced, thus also reducing the system response time. Based on our results, the buffer size
and the system response time can be reduced by half or more. These findings are essential for constructing video-on-demand
systems that provide satisfactory performance. 相似文献
14.
David Gibson Jon Kleinberg Prabhakar Raghavan 《The VLDB Journal The International Journal on Very Large Data Bases》2000,8(3-4):222-236
We describe a novel approach for clustering collections of sets, and its application to the analysis and mining of categorical
data. By “categorical data,” we mean tables with fields that cannot be naturally ordered by a metric – e.g., the names of
producers of automobiles, or the names of products offered by a manufacturer. Our approach is based on an iterative method
for assigning and propagating weights on the categorical values in a table; this facilitates a type of similarity measure
arising from the co-occurrence of values in the dataset. Our techniques can be studied analytically in terms of certain types
of non-linear dynamical systems.
Received February 15, 1999 / Accepted August 15, 1999 相似文献
15.
I/O scheduling for digital continuous media 总被引:4,自引:0,他引:4
A growing set of applications require access to digital video and audio. In order to provide playback of such continuous
media (CM), scheduling strategies for CM data servers (CMS) are necessary. In some domains, particularly defense and industrial process control, the timing requirements of these applications
are strict and essential to their correct operation. In this paper we develop a scheduling strategy for multiple access to
a CMS such that the timing guarantees are maintained at all times. First, we develop a scheduling strategy for the steady state,
i.e., when there are no changes in playback rate or operation. We derive an optimal Batched SCAN (BSCAN) algorithm that requires minimum buffer space to schedule concurrent accesses. The scheduling strategy incorporates two key
constraints: (1) data fetches from the storage system are assumed to be in integral multiples of the block size, and (2) playback
guarantees are ensured for frame-oriented streams when each frame can span multiple blocks. We discuss modifications to the
scheduling strategy to handle compressed data like motion-JPEG and MPEG.
Second, we develop techniques to handle dynamic changes brought about by VCR-like operations executed by applications. We define a suite of primitive VCR-like operations that can be executed. We show that an unregulated change in the BSCAN schedule, in response to VCR-like operations, will affect playback guarantees. We develop two general techniques to ensure playback guarantees while responding
to VCR-like operations: passive and active accumulation. Using user response time as a metric we show that active accumulation algorithms
outperform passive accumulation algorithms. An optimal response-time algorithm in a class of active accumulation strategies
is derived. The results presented here are validated by extensive simulation studies. 相似文献
16.
In a video-on-demand (VOD) environment, disk arrays are often used to support the disk bandwidth requirement. This can pose
serious problems on available disk bandwidth upon disk failure. In this paper, we explore the approach of replicating frequently
accessed movies to provide high data bandwidth and fault tolerance required in a disk-array-based video server. An isochronous
continuous video stream imposes different requirements from a random access pattern on databases or files. Explicitly, we
propose a new replica placement method, called rotational mirrored declustering (RMD), to support high data availability for disk arrays in a VOD environment. In essence, RMD is similar to the conventional
mirrored declustering in that replicas are stored in different disk arrays. However, it is different from the latter in that
the replica placements in different disk arrays under RMD are properly rotated. Combining the merits of prior chained and
mirrored declustering methods, RMD is particularly suitable for storing multiple movie copies to support VOD applications.
To assess the performance of RMD, we conduct a series of experiments by emulating the storage and delivery of movies in a
VOD system. Our results show that RMD consistently outperforms the conventional methods in terms of load-balancing and fault-tolerance
capability after disk failure, and is deemed a viable approach to supporting replica placement in a disk-array-based video
server. 相似文献
17.
D. Laurent J. Lechtenbörger N. Spyratos G. Vossen 《The VLDB Journal The International Journal on Very Large Data Bases》2001,10(4):295-315
Views over databases have regained attention in the context of data warehouses, which are seen as materialized views. In this setting, efficient view maintenance is an important issue, for which the notion of self-maintainability has been identified as desirable. In this paper, we extend the concept of self-maintainability to (query and update) independence within a formal framework, where independence with respect to arbitrary given sets of queries and updates over the sources
can be guaranteed. To this end we establish an intuitively appealing connection between warehouse independence and view complements. Moreover, we study special kinds of complements, namely monotonic complements, and show how to compute minimal ones in the presence of keys and foreign keys in the underlying databases. Taking advantage
of these complements, an algorithmic approach is proposed for the specification of independent warehouses with respect to
given sets of queries and updates.
Received: 21 November 2000 / Accepted: 1 May 2001 Published online: 6 September 2001 相似文献
18.
Efficient similarity search for market basket data 总被引:2,自引:0,他引:2
Alexandros Nanopoulos Yannis Manolopoulos 《The VLDB Journal The International Journal on Very Large Data Bases》2002,11(2):138-152
Several organizations have developed very large market basket databases for the maintenance of customer transactions. New
applications, e.g., Web recommendation systems, present the requirement for processing similarity queries in market basket
databases. In this paper, we propose a novel scheme for similarity search queries in basket data. We develop a new representation
method, which, in contrast to existing approaches, is proven to provide correct results. New algorithms are proposed for the
processing of similarity queries. Extensive experimental results, for a variety of factors, illustrate the superiority of
the proposed scheme over the state-of-the-art method.
Edited by R. Ng. Received: August 6, 2001 / Accepted: May 21, 2002 Published online: September 25, 2002 相似文献
19.
Data partitioning and load balancing in parallel disk systems 总被引:13,自引:0,他引:13
Peter Scheuermann Gerhard Weikum Peter Zabback 《The VLDB Journal The International Journal on Very Large Data Bases》1998,7(1):48-66
Parallel disk systems provide opportunities for exploiting I/O parallelism in two possible ways, namely via inter-request
and intra-request parallelism. In this paper, we discuss the main issues in performance tuning of such systems, namely striping
and load balancing, and show their relationship to response time and throughput. We outline the main components of an intelligent,
self-reliant file system that aims to optimize striping by taking into account the requirements of the applications, and performs
load balancing by judicious file allocation and dynamic redistributions of the data when access patterns change. Our system
uses simple but effective heuristics that incur only little overhead. We present performance experiments based on synthetic
workloads and real-life traces.
Received May 17, 1994 / Accepted June 9, 1997 相似文献
20.
Analog computation for phase-based disparity estimation: continuous and discrete models 总被引:4,自引:0,他引:4
Bruno Crespi Alex G. Cozzi Luigi Raffo Silvio Sabatini 《Machine Vision and Applications》1998,11(2):83-95
The analog implementation of a phase-based technique for disparity estimation is discussed. This technique is based on the
convolution of images with Gabor filters. The article shows that by replacing the Gaussian envelope with other envelopes,
the convolution operation is equivalent to the solution of a system of differential equations, whose order is related to the
smoothness of the kernel. A detailed comparison between the disparity estimates obtained using these kernels and those obtained
using the standard filter is presented. The discretization of the model leads to lattice networks in which the number of connections
per node required to perform convolution is limited to the first few nearest neighbors. The short connection length makes
these filter suitable for analog VLSI implementation, for which the number of connection per node is a crucial factor. Experimental
measures on a prototype CMOS 17-node chip validated the approach.
Received: 27 October 1997 / Accepted: 18 June 1998 相似文献