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1.
Issues in the design of a storage server for video-on-demand 总被引:2,自引:0,他引:2
Antoine N. Mourad 《Multimedia Systems》1996,4(2):70-86
We examine issues related to the design
of a storage server for video-on-demand (VOD) applications.
The storage medium considered is magnetic disks
or arrays of disks. We investigate disk scheduling policies,
buffer management policies and I/O bus protocol issues.
We derive the number of sessions that can be
supported from a single disk or an array of disks and determine the
amount of buffering required to support a given number of users.
Furthermore,
we propose a scheduling mechanism for disk accesses that significantly
lowers the buffer-size requirements in the case of disk arrays.
The buffer size required under the proposed scheme is independent
of the number of disks in the array. This property allows for striping
video content over a large number of disks to achieve higher
concurrency in access to a particular video object.
This enables the server to satisfy hundreds of independent requests
to the same video object or to hundreds of different objects while
storing only one copy of each video object.
The reliability implications of striping content over a large number of disks
are addressed and two solutions are proposed.
Finally, we examine various policies for dealing with disk thermal calibration
and the placement of videos on disks and disk arrays. 相似文献
2.
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
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.
Transporting QoS adaptive flows 总被引:4,自引:0,他引:4
Distributed audio and video applications need to adapt to fluctuations in delivered quality of service (QoS). By trading
off temporal and spatial quality to available bandwidth, or manipulating the playout time of continuous media in response
to variation in delay, audio and video flows can be made to adapt to fluctuating QoS with minimal perceptual distortion. In
this paper, we extend our previous work on a QoS Architecture (QoS-A) by populating the QoS management planes of our architecture
with a framework for the control and management of multilayer coded flows operating in heterogeneous multimedia networking
environments. Two key techniques are proposed: i) an end-to-end rate-shaping scheme which adapts the rate of MPEG-coded flows
to the available network resources while minimizing the distortion observed at the receiver; and ii) an adaptive network service,
which offers “hard” guarantees to the base layer of multilayer coded flows and “fairness” guarantees to the enhancement layers
based on a bandwidth allocation technique called Weighted Fair Sharing. 相似文献
5.
Dynamic batching policies for an on-demand video server 总被引:18,自引:0,他引:18
In a video-on-demand environment, continuous delivery of video streams to the clients is guaranteed by sufficient reserved
network and server resources. This leads to a hard limit on the number of streams that a video server can deliver. Multiple
client requests for the same video can be served with a single disk I/O stream by sending (multicasting) the same data blocks
to multiple clients (with the multicast facility, if present in the system). This is achieved by batching (grouping) requests
for the same video that arrive within a short time. We explore the role of customer-waiting time and reneging behavior in
selecting the video to be multicast. We show that a first come, first served (FCFS) policy that schedules the video with
the longest outstanding request can perform better than the maximum queue length (MQL) policy that chooses the video with
the maximum number of outstanding requests. Additionally, multicasting is better exploited by scheduling playback of the
most popular videos at predetermined, regular intervals (hence, termed FCFS-). If user reneging can be reduced by guaranteeing that a maximum waiting time will not be exceeded, then performance of FCFS- is further improved by selecting the regular playback intervals as this maximum waiting time. For an empirical workload,
we demonstrate a substantial reduction (of the order of 60%) in the required server capacity by batching. 相似文献
6.
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
7.
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
8.
Handling a tertiary storage device, such as an optical disk library, in the framework of a disk-based stream service model,
requires a sophisticated streaming model for the server, and it should consider the device-specific performance characteristics
of tertiary storage. This paper discusses the design and implementation of a video server which uses tertiary storage as a
source of media archiving. We have carefully designed the streaming mechanism for a server whose key functionalities include
stream scheduling, disk caching and admission control. The stream scheduling model incorporates the tertiary media staging
into a disk-based scheduling process, and also enhances the utilization of tertiary device bandwidth. The disk caching mechanism
manages the limited capacity of the hard disk efficiently to guarantee the availability of media segments on the hard disk.
The admission controller provides an adequate mechanism which decides upon the admission of a new request based on the current
resource availability of the server. The proposed system has been implemented on a general-purpose operating system and it
is fully operational. The design principles of the server are validated with real experiments, and the performance characteristics
are analyzed. The results guide us on how servers with tertiary storage should be deployed effectively in a real environment.
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ID="*" e-mail: hjcha@cs.yonsei.ac.kr 相似文献
9.
随着视频点播、视频会议、视频监控、数字图书馆等流媒体应用的普及,流媒体服务器存储资源管理成为制约服务质量的瓶颈之一。根据多媒体服务器的性能要求,提出了一种支持QoS的磁盘调度策略。它由三个主要部分组成:探测模块、负载监测模块和自适应管理模块。探测模块,负责判断当前的资源情况能否满足服务请求;自适应模块,根据负载监删模块检测到的负载变化情况,动态调整服务周期在实时请求和尽力服务请求之间的分配。实验表明此磁盘调度策略能在保证实时请求无抖动执行的同时,明显减少了非实时请求的响应时间。 相似文献
10.
Xiaodong Wen Theodore D. Huffmire Helen H. Hu Adam Finkelstein 《Multimedia Systems》1999,7(5):350-358
We present several algorithms suitable for analysis of broadcast video. First, we show how wavelet analysis of frames of
video can be used to detect transitions between shots in a video stream, thereby dividing the stream into segments. Next we
describe how each segment can be inserted into a video database using an indexing scheme that involves a wavelet-based “signature.”
Finally, we show that during a subsequent broadcast of a similar or identical video clip, the segment can be found in the
database by quickly searching for the relevant signature. The method is robust against noise and typical variations in the
video stream, even global changes in brightness that can fool histogram-based techniques. In the paper, we compare experimentally
our shot transition mechanism to a color histogram implementation, and also evaluate the effectiveness of our database-searching
scheme. Our algorithms are very efficient and run in realtime on a desktop computer. We describe how this technology could
be employed to construct a “smart VCR” that was capable of alerting the viewer to the beginning of a specific program or identifying 相似文献
11.
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
12.
Multimedia systems store and retrieve large amounts of data which require extremely high disk bandwidth and their performance
critically depends on the efficiency of disk storage. However, existing magnetic disks are designed for small amounts of data
retrievals geared to traditional operations; with speed improvements mainly focused on how to reduce seek time and rotational
latency. When the same mechanism is applied to multimedia systems, overheads in disk I/O can result in dramatic deterioration
in system performance. In this paper, we present a mathematical model to evaluate the performance of constant-density recording
disks, and use this model to analyze quantitatively the performance of multimedia data request streams. We show that high
disk throughput may be achieved by suitably adjusting the relevant parameters. In addition to demonstrating quantitatively
that constant-density recording disks perform significantly better than traditional disks for multimedia data storage, a novel
disk-partitioning scheme which places data according to their bandwidths is presented. 相似文献
13.
Periodic broadcasting can be used to support near-video-on-demand for popular videos. For a given bandwidth allocation, pyramid
broadcasting schemes substantially reduce the viewer latency (waiting) time compared to conventional broadcasting schemes.
Nevertheless, such pyramid schemes typically have substantial storage requirements at the client end, and this results in
set-top boxes needing disks with high transfer rate capabilities. In this paper, we present a permutation-based pyramid scheme
in which the storage requirements and disk transfer rates are greatly reduced, and yet the viewer latency is also smaller.
Under the proposed approach, each video is partitioned into contiguous segments of geometrically increasing sizes, and each
segment is further divided into blocks, where a block is the basic unit of transmission. As in the original pyramid scheme,
frequencies of transmission for the different segments of a video vary in a manner inversely proportional to their size. Instead
of transmitting the blocks in each segment in sequential order, the proposed scheme transmits these blocks in a prespecified
cyclic permutation to save on storage requirements in the client end. Performance analyses are provided to quantify the benefits
of the new scheme. 相似文献
14.
Igor D.D. Curcio Antonio Puliafito Salvatore Riccobene Lorenzo Vita 《Multimedia Systems》1998,6(6):367-381
The relative simplicity of access to digital communications nowadays and the simultaneous increase in the available bandwidth
are leading to the definition of new telematic services, mainly oriented towards multimedia applications and interactivity
with the user. In the near future, a decisive role will be played in this scenario by the providers of interactive multimedia
services of the on-demand type, which will guarantee the end user a high degree of flexibility, speed and efficiency. In this
paper, some of the technical aspects regarding these service providers are dealt with, paying particular attention to the
problems of storing information and managing service requests. More specifically, the paper presents and evaluates a new storage
technique based on the use of disk array technology, which can manage both typical multimedia connections and traditional
requests. The proposed architecture is based on the joint use of the partial dynamic declustering and the information dispersal
algorithm, which are employed for the allocation and retrieval of the data stored on the disk array. We also define efficient
strategies for request management in such a way as to meet the time constraints imposed by multimedia sessions and guarantee
good response times for the rest of the traffic. The system proposed is then analyzed using a simulation approach. 相似文献
15.
Michiharu Kudo 《International Journal of Information Security》2002,1(2):116-130
Over the years a wide variety of access control models and policies have been proposed, and almost all the models have assumed
“grant the access request or deny it.” They do not provide any mechanism that enables us to bind authorization rules with
required operations such as logging and encryption. We propose the notion of a “provisional action” that tells the user that
his request will be authorized provided he (and/or the system) takes certain actions. The major advantage of our approach
is that arbitrary actions such as cryptographic operations can all coexist in the access control policy rules. We define a
fundamental authorization mechanism and then formalize a provision-based access control model. We also present algorithms
and describe their algorithmic complexity. Finally, we illustrate how provisional access control policy rules can be specified
effectively in practical usage scenarios.
Published online: 22 January 2002 相似文献
16.
ExploreNet is an experimental environment for creating and delivering networked “virtual worlds.” This system's style of user
interaction was inspired by the concept of a “habitat” as first articulated in the LucasFilm's Habitat system. Players enter
and interact in a habitat via their animated alter egos, called “avatars.” Habitats may be created for many purposes, including
social interaction, entertainment and education. Our focus has been to facilitate the creation of habitats in which virtual
communities of learners and mentors interact. This paper presents details of the current ExploreNet system, including its
user interface, the means it provides for creating complex behaviors, details of its implementation, the outcomes of several
experiments using this system, and our plans for its natural migration to a World Wide Web-based system. 相似文献
17.
Disk scheduling in video editing systems 总被引:2,自引:0,他引:2
Aref W.G. Kamel I. Ghandeharizadeh S. 《Knowledge and Data Engineering, IEEE Transactions on》2001,13(6):933-950
Modern video servers support both video-on-demand and nonlinear editing applications. Video-on-demand servers enable the user to view video clips or movies from a video database, while nonlinear editing systems enable the user to manipulate the content of the video database. Applications such as video and news editing systems require that the underlying storage server be able to concurrently record live broadcast information, modify prerecorded data, and broadcast an authored presentation. A multimedia storage server that efficiently supports such a diverse group of activities constitutes the focus of this study. A novel real-time disk scheduling algorithm is presented that treats both read and write requests in a homogeneous manner in order to ensure that their deadlines are met. Due to real-time demands of movie viewing, read requests have to be fulfilled within certain deadlines; otherwise, they are considered lost. Since the data to be written into disk is stored in main memory buffers, write requests can be postponed until critical read requests are processed. However, write requests still have to be processed within reasonable delays and without the possibility of indefinite postponement. This is due to the physical constraint of the limited size of the main memory write buffers. The new algorithm schedules both read and write requests appropriately, to minimize the amount of disk reads that do not meet their presentation deadlines, and to avoid indefinite postponement and large buffer sizes in the case of disk writes. Simulation results demonstrate that the proposed algorithm offers low violations of read deadlines, reduces waiting time for lower priority disk requests, and improves the throughput of the storage server by enhancing the utilization of available disk bandwidth 相似文献
18.
19.
In this paper, we present an efficient approach for supporting fast-scanning (FS) operations in MPEG-based video-on-demand
(VOD) systems. This approach is based on storing multiple, differently encoded versions of the same movie at the server. A
normal version is used for normal playback, while several scan versions are used for FS. Each scan version supports forward and backward FS at a given speedup. The server responds to an FS request
by switching from the normal version to an appropriate scan version. Scanning versions are produced by encoding a sample of
the raw frames using the same GOP pattern of the normal version. When a scanning version is decoded and played back at the
normal frame rate, it gives a perceptual motion speedup. By being able to control the traffic envelopes of the scan versions,
our approach can be integrated into a previously proposed framework for distributing archived, MPEG-coded video streams. FS
operations are supported using no or little extra network bandwidth beyond what is already allocated for normal playback.
Mechanisms for controlling the traffic envelopes of the scan versions are presented. The actions taken by the server and the
client's decoder in response to various types of interactive requests are described in detail. The latency incurred in implementing
various interactive requests is shown to be within an acceptable range. Striping and disk-scheduling strategies for storing
various versions at the server are presented. Issues related to the implementation of our approach are discussed. 相似文献
20.
Popularity-based assignment of movies to storage devices in a video-on-demand system 总被引:4,自引:0,他引:4
A video-on-demand server must satisfy a large customer base and a diverse archive of movies under changing movie popularity and daily load peaks. These requirements must be satisfied under the constraints imposed by storage device costs, capacities, I/O bandwidths, and geographic locations. In this paper we describe a partitioning of video data (movies) onto a video-on-demand storage hierarchy to achieve efficient storage and I/O bandwidth use. Our approach uses a probabilistic model of movie popularity in data distribution and replication to balance user requests with available disk I/O bandwidth. The results can be applied in the design of a general, distributed video-on-demand system. 相似文献