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1.
Due to recent advances in network, storage and data compression technologies, video-on-demand (VOD) service has become economically
feasible. It is a challenging task to design a video storage server that can efficiently service a large number of concurrent
requests on demand. One approach to accomplishing this task is to reduce the I/O demand to the VOD server through data- and
resource-sharing techniques. One form of data sharing is the stream-merging approach proposed in [5]. In this paper, we formalize a static version of the stream-merging problem, derive an upper bound on the
I/O demand of static stream merging, and propose efficient heuristic algorithms for both static and dynamic versions of the
stream-merging problem. 相似文献
2.
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
3.
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
4.
Integrated document caching and prefetching in storage hierarchies based on Markov-chain predictions
Achim Kraiss Gerhard Weikum 《The VLDB Journal The International Journal on Very Large Data Bases》1998,7(3):141-162
Large multimedia document archives may hold a major fraction of their data in tertiary storage libraries for cost reasons.
This paper develops an integrated approach to the vertical data migration between the tertiary, secondary, and primary storage
in that it reconciles speculative prefetching, to mask the high latency of the tertiary storage, with the replacement policy
of the document caches at the secondary and primary storage level, and also considers the interaction of these policies with
the tertiary and secondary storage request scheduling.
The integrated migration policy is based on a continuous-time Markov chain model for predicting the expected number of accesses
to a document within a specified time horizon. Prefetching is initiated only if that expectation is higher than those of the
documents that need to be dropped from secondary storage to free up the necessary space. In addition, the possible resource
contention at the tertiary and secondary storage is taken into account by dynamically assessing the response-time benefit
of prefetching a document versus the penalty that it would incur on the response time of the pending document requests.
The parameters of the continuous-time Markov chain model, the probabilities of co-accessing certain documents and the interaction
times between successive accesses, are dynamically estimated and adjusted to evolving workload patterns by keeping online
statistics. The integrated policy for vertical data migration has been implemented in a prototype system. The system makes
profitable use of the Markov chain model also for the scheduling of volume exchanges in the tertiary storage library. Detailed
simulation experiments with Web-server-like synthetic workloads indicate significant gains in terms of client response time.
The experiments also show that the overhead of the statistical bookkeeping and the computations for the access predictions
is affordable.
Received January 1, 1998 / Accepted May 27, 1998 相似文献
5.
As the number of video streams to be supported by a digital video delivery system (DVDS) increases, an improved understanding
of the necessity for reliable and cost-efficient support for a considerable number of video streams (in the magnitude of tens
of thousands), and the dependency largely on software capabilities emerges. Even in the presence of an optimal hardware configuration,
or model, and associated costs, using software to exploit the underlying hardware capabilities is of paramount importance.
Although a number of DVDSs have become operational, their ability to deliver the required services mainly depends on the small
number of streams supported and the hardware trade-offs. It is imperative that current software developments account for
the eventual scalability of the number of video streams without commensurate increase in hardware. In this paper, we present
strategies for the management of video streams in order to maintain and satisfy their space and time requirements. We use
a DVDS architectural model with functionally dichotomized nodes: a single-node partition is responsible for data retrieval,
while the remaining partition of nodes accepts user requests, determines object locations, and routes requests through the
network that connects both partitions. We present a detailed analysis of the issues related to queuing I/O requests and data
buffering. The discussion includes the requirements for arranging and scheduling I/O requests and data buffers, with the objective
of guaranteeing the required data availability rates for continuous media display. 相似文献
6.
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
7.
Kelvin K.W. Law John C.S. Lui Leana Golubchik 《The VLDB Journal The International Journal on Very Large Data Bases》1999,8(2):133-153
Advances in high-speed networks and multimedia technologies have made it feasible to provide video-on-demand (VOD) services
to users. However, it is still a challenging task to design a cost-effective VOD system that can support a large number of
clients (who may have different quality of service (QoS) requirements) and, at the same time, provide different types of VCR
functionalities. Although it has been recognized that VCR operations are important functionalities in providing VOD service,
techniques proposed in the past for providing VCR operations may require additional system resources, such as extra disk I/O,
additional buffer space, as well as network bandwidth. In this paper, we consider the design of a VOD storage server that
has the following features: (1) provision of different levels of display resolutions to users who have different QoS requirements,
(2) provision of different types of VCR functionalities, such as fast forward and rewind, without imposing additional demand
on the system buffer space, I/O bandwidth, and network bandwidth, and (3) guarantees of the load-balancing property across
all disks during normal and VCR display periods. The above-mentioned features are especially important because they simplify
the design of the buffer space, I/O, and network resource allocation policies of the VOD storage system. The load-balancing
property also ensures that no single disk will be the bottleneck of the system. In this paper, we propose data block placement,
admission control, and I/O-scheduling algorithms, as well as determine the corresponding buffer space requirements of the
proposed VOD storage system. We show that the proposed VOD system can provide VCR and multi-resolution services to the viewing
clients and at the same time maintain the load-balancing property.
Received June 9, 1998 / Accepted April 26, 1999 相似文献
8.
HweeHwa Pang 《Multimedia Systems》1997,5(6):386-399
Multimedia applications that are required to manipulate large collections of objects are becoming increasingly common. Moreover,
the size of multimedia objects, which are already huge, are getting even bigger as the resolution of output devices improve.
As a result, many multimedia storage systems are not likely to be able to keep all of their objects disk-resident. Instead,
a majority of the less popular objects have to be off-loaded to tertiary storage to keep costs down. The speed at which objects
can be accessed from tertiary storage is thus an important consideration. In this paper, we propose an adaptive data retrieval
algorithm that employs a combination of staging and direct access in servicing tertiary storage retrieval requests. At retrieval
time, an object that resides in tertiary storage can either be staged to and then played back from disks, or the object can
be accessed directly from the tertiary drives. We show that a simplistic policy that adheres strictly to staging or direct
access does not exploit the full retrieval capacity of both the tertiary library and the secondary storage. To overcome the
problem, we propose a data retrieval algorithm that dynamically chooses between staging and direct access, based on the relative
load on the tertiary versus secondary devices. A series of simulation experiments confirms that the algorithm achieves good
access times over a wide range of workloads and resource configurations. Moreover, the algorithm is very responsive to changing
load conditions. 相似文献
9.
Efficient admission control algorithms for multimedia servers 总被引:3,自引:0,他引:3
In this paper, we have proposed efficient admission control algorithms for multimedia storage servers that are providers
of variable-bit-rate media streams. The proposed schemes are based on a slicing technique and use aggressive methods for admission
control. We have developed two types of admission control schemes: Future-Max (FM) and Interval Estimation (IE). The FM algorithm uses the maximum bandwidth requirement of the future to estimate the bandwidth requirement. The IE
algorithm defines a class of admission control schemes that use a combination of the maximum and average bandwidths within
each interval to estimate the bandwidth requirement of the interval. The performance evaluations done through simulations
show that the server utilization is improved by using the FM and IE algorithms. Furthermore, the quality of service is also
improved by using the FM and IE algorithms. Several results depicting the trade-off between the implementation complexity,
the desired accuracy, the number of accepted requests, and the quality of service are presented. 相似文献
10.
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
11.
A large-scale, distributed video-on-demand (VOD) system allows geographically dispersed residential and business users to
access video services, such as movies and other multimedia programs or documents on demand from video servers on a high-speed
network. In this paper, we first demonstrate through analysis and simulation the need for a hierarchical architecture for
the VOD distribution network.We then assume a hierarchical architecture, which fits the existing tree topology used in today's
cable TV (CATV) hybrid fiber/coaxial (HFC) distribution networks. We develop a model for the video program placement, configuration,
and performance evaluation of such systems. Our approach takes into account the user behavior, the fact that the user requests
are transmitted over a shared channel before reaching the video server containing the requested program, the fact that the
input/output (I/O) capacity of the video servers is the costlier resource, and finally the communication cost. In addition,
our model employs batching of user requests at the video servers. We study the effect of batching on the performance of the
video servers and on the quality of service (QoS) delivered to the user, and we contribute dynamic batching policies which
improve server utilization, user QoS, and lower the servers' cost. The evaluation is based on an extensive analytical and
simulation study. 相似文献
12.
We present a high-performance solution to the I/O retrieval problem in a distributed multimedia system. Parallelism of data
retrieval is achieved by striping the data across multiple disks. We identify the components that contribute to media data-retrieval
delay. The variable delays among these have a great bearing on the server throughput under varying load conditions. We present
a buffering scheme to minimize these variations. We have implemented our model on the Intel Paragon parallel computer. The
results of component-wise instrumentation of the server operation are presented and analyzed. Experimental results that demonstrate
the efficacy of the buffering scheme are presented. Based on our experiments, a dynamic admission-control policy that takes
server workloads into account is proposed. 相似文献
13.
Providing QOS guarantees for disk I/O 总被引:1,自引:0,他引:1
In this paper, we address the problem of providing different levels of performance guarantees or quality of service for disk
I/O. We classify disk requests into three categories based on the provided level of service. We propose an integrated scheme
that provides different levels of performance guarantees in a single system. We propose and evaluate a mechanism for providing
deterministic service for variable-bit-rate streams at the disk. We will show that, through proper admission control and bandwidth
allocation, requests in different categories can be ensured of performance guarantees without getting impacted by requests
in other categories. We evaluate the impact of scheduling policy decisions on the provided service. We also quantify the improvements
in stream throughput possible by using statistical guarantees instead of deterministic guarantees in the context of the proposed
approach. 相似文献
14.
Francesco Garibaldo 《AI & Society》2002,16(4):305-331
This article, first of all, supports the idea that the undeniable process of ICT-based technological convergence implies
the social, cultural and business unification of the world of media and culture. The poor performance of the megamerger is
a clear indicator of the unstable ground of the convergence hypothesis. Secondly, it argues in favour of cooperation between
different expertise, skills and cultures to make multimedia products or to supply multimedia services, instead of creating
from scratch a brand new class of hybrid skills and professions. Thirdly, a variety of new possible and realistically achievable
professional profiles in cultural industries and institutions are illustrated. Eventually a set of public policies, in the
light of a new role for cities and regions, is developed.
Correspondence and offprint requests to: Francesco Garibaldo, Fondazione ‘Istituto Per il Lavoro (IPL)’, via Marconi 8, 40122 Bologna, Italy. Email: f.garibaldo@ipielle.emr.it 相似文献
15.
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
16.
Recent advances in computer technologies have made it feasible to provide multimedia services, such as news distribution
and entertainment, via high-bandwidth networks. The storage and retrieval of large multimedia objects (e.g., video) becomes
a major design issue of the multimedia information system. While most other works on multimedia storage servers assume an
on-line disk storage system, we consider a two-tier storage architecture with a robotic tape library as the vast near-line
storage and an on-line disk system as the front-line storage. Magnetic tapes are cheaper, more robust, and have a larger
capacity; hence, they are more cost effective for large scale storage systems (e.g., video-on-demand (VOD) systems may
store tens of thousands of videos). We study in detail the design issues of the tape subsystem and propose some novel tape-scheduling
algorithms which give faster response and require less disk buffer space. We also study the disk-striping policy and the
data layout on the tape cartridge in order to fully utilize the throughput of the robotic tape system and to minimize the
on-line disk storage space. 相似文献
17.
In this paper, we present a novel approach for multimedia data indexing and retrieval that is machine independent and highly
flexible for sharing multimedia data across applications. Traditional multimedia data indexing and retrieval problems have
been attacked using the central data server as the main focus, and most of the indexing and query-processing for retrieval
are highly application dependent. This precludes the use of created indices and query processing mechanisms for multimedia
data which, in general, have a wide variety of uses across applications. The approach proposed in this paper addresses three
issues: 1. multimedia data indexing; 2. inference or query processing; and 3. combining indices and inference or query mechanism
with the data to facilitate machine independence in retrieval and query processing. We emphasize the third issue, as typically
multimedia data are huge in size and requires intra-data indexing. We describe how the proposed approach addresses various
problems faced by the application developers in indexing and retrieval of multimedia data. Finally, we present two applications
developed based on the proposed approach: video indexing; and video content authorization for presentation. 相似文献
18.
Thomas A. Mueck Martin L. Polaschek 《The VLDB Journal The International Journal on Very Large Data Bases》1997,6(4):312-332
With respect to the specific requirements of advanced OODB applications, index data structures for type hierarchies in OODBMS
have to provide efficient support for multiattribute queries and have to allow index optimization for a particular query profile.
We describe the multikey type index and an efficient implementation of this indexing scheme. It meets both requirements: in addition to its multiattribute query
capabilities it is designed as a mediator between two standard design alternatives, key-grouping and type-grouping. A prerequisite
for the multikey type index is a linearization algorithm which maps type hierarchies to linearly ordered attribute domains
in such a way that each subhierarchy is represented by an interval of this domain. The algorithm extends previous results
with respect to multiple inheritance. The subsequent evaluation of our proposal focuses on storage space overhead as well
as on the number of disk I/O operations needed for query execution. The analytical results for the multikey type index are
compared to previously published figures for well-known single-key search structures. The comparison clearly shows the superiority
of the multikey type index for a large class of query profiles.
Edited by E. Bertino. Received October 7, 1996 / Accepted March 28, 1997 相似文献
19.
Due to their large bandwidth demand and synchronization requirements, multimedia applications, in general, consume buffers
of huge size, which prevents potential customers from using multimedia services. We recognize the problem and propose a hierarchical
architecture to reduce the buffer size. The architecture can be applied to both 1- and - applications. We establish the architecture by first determining neighbor sets and then applying a grouping algorithm and
a renegotiation process. This architecture can also meet the synchronization requirements of multimedia applications. We evaluate
the performance of the architecture through simulations and compare it with that of a direct connection architecture. The result shows that the hierarchical architecture reduces the buffer size significantly without
serious penalty to the total bandwidth and without introducing extra hot spots. 相似文献
20.
In this work, we propose a novel hard disk technique, “AV Disk”, for modern multimedia applications. Modern hard disk drives
adopt complex sector layout mechanisms to reduce track and head switch overhead. While these complex sector layout mechanism
can reduce average overhead involved in the track and head switch, they bring larger variability in the overhead. From a multimedia
application’s point of view, it is important to minimize the worst case I/O latency rather than to improve the average IO
latency. We focus our effort to minimize track switch overhead as well as the variability in track switch overhead involved
in disk I/O. We propose that track of the hard disk drive is aligned with a certain IO size. In this work, we develop an elaborate
performance model with which we can compute the optimal IO unit size for multimedia applications. We propose that hard disk
controller is responsible for positioning data blocks in the hard disk platter in such a manner that I/O units are not placed
across the track boundaries, where a single I/O unit has size of 32–128 KByte. Optimal IO unit size is used in aligning the
tracks in hard disk drives. We develop Skewed Sector Sparing technique in aligning a track with a given IO size. However,
when the I/O unit for alignment is increased to 128 KByte, 17% of the disk space becomes unusable. Despite the decreased storage
area, track aligning technique increases the overall performance of the hard disk. According to our simulation-based experiment,
overall disk performance increases about 5–25%. Given that capacity of hard disk increases 100% every year, we cautiously
regard it as reasonable tradeoff to increase the I/O latency of the disk. 相似文献