共查询到20条相似文献,搜索用时 234 毫秒
1.
2.
The promise of a broadband integrated service digital network has led to the design of mechanisms for efficient transport
of real-time compressed video in packet switching networks. We examine feedback control for video transport in ATM networks
where the available feedback is a single bit of information carried in the cell header. We investigate the performance of
three single-bit schemes for source rate adaptation. Two were originally for congestion control of bursty data traffic and
are modified to control video traffic. The third scheme conveys more information about
the state of queue(s) at the bottleneck. The simulation results show that all three schemes for feedback control of VBR video
streams work remarkably well. During severe network congestion, the signal quality degrades gracefully, but not uniformly
across all connections. Based on insights from the initial simulations, we propose a scheme to improve the fairness of service
and demonstrate its effectiveness. 相似文献
3.
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
4.
To support emerging real-time applications, high-speed integrated services networks must provide end-to-end performance guarantees
on a per-connection basis in a networking environment. Resource management algorithms must accommodate traffic that may get
burstier as it traverses the network due to complex interactions among packet streams at each switch. To address this problem,
several non-work-conserving packet-service disciplines have been proposed. Non-work-conserving servers may be idle and hold
packets under certain conditions, to reconstruct, fully or partially, the traffic pattern of the original source inside the
network and prevent the traffic from becoming burstier. We compare two non-work-conserving service disciplines. Stop-and-go
uses a multilevel framing strategy to allocate resources in a single switch and to ensure traffic smoothness throughout the
network. Rate controlled static priority (RCSP) decouples the server functions with two components: (1) a regulator to control
traffic distortion introduced by multiplexing effects and load fluctuations in previous servers, and 2) a static priority
scheduler to multiplex the regulated traffic. We compare the two service disciplines in terms of traffic specification, scheduling
mechanism, buffer space requirement, end-to-end delay characteristics, connection admission-control algorithms, and achievable
network utilization. The comparison is first done analytically, and then empirically by using two 10-min traces of MPEG compressed
video. 相似文献
5.
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
6.
Multimedia systems must be able to support a certain quality of service (QoS) to satisfy the stringent real-time performance
requirements of their applications. HeiRAT, the Heidelberg Resource Administration Technique, is a comprehensive QoS management
system that was designed and implemented in connection with a distributed multimedia platform for networked PCs and workstations.
HeiRAT includes techniques for QoS negotiation, QoS calculation, resource reservation, and resource scheduling for local and
network resources. 相似文献
7.
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
8.
Previous works showed that the quality-of-service (QoS) requirements of multimedia applications can be optimally satisfied by pipeline forwarding (PF) by providing end-to-end delay guarantees as well as high network resource utilization. However, the unavoidable mismatch between reserved resources and the unpredictable traffic profile of a video stream has an impact on the resulting application layer quality. Therefore, a new low-complexity H.264 video encoding and packetization scheme based on a distortion-optimized macroblock grouping technique is designed here to maximize the performance of video transmission on PF networks. The scheme considers the perceptual importance of the different parts of the video data to group the most important information in few packets that are the natural candidates to receive the deterministic service provided by PF. Results show peak signal-to-noise ratio (PSNR) gains up to 2.5 dB over traditional video encoding and packetization schemes, as well as more graceful degradation in case of high network load. 相似文献
9.
Min Wu Joyce R.A. Hau-San Wong Long Guan Sun-Yuan Kung 《Multimedia, IEEE Transactions on》2001,3(2):186-199
The reliable and efficient transmission of high-quality variable bit rate (VBR) video through the Internet generally requires network resources be allocated in a dynamic fashion. This includes the determination of when to renegotiate for network resources, as well as how much to request at a given time. The accuracy of any resource request method depends critically on its prediction of future traffic patterns. Such a prediction can be performed using the content and traffic information of short video segments. This paper presents a systematic approach to select the best features for prediction, indicating that while content is important in predicting the bandwidth of a video hit stream, the use of both content and available short-term bandwidth statistics can yield significant improvements. A new framework for traffic prediction is proposed in this paper; experimental results show a smaller mean-square resource prediction error and higher overall link utilization 相似文献
10.
A buffer-inventory-based dynamic scheduling algorithm for multimedia-on-demand servers 总被引:2,自引:0,他引:2
We present a producer-consumer model of multimedia-on-demand (MOD) servers. The producer retrieves media data from a disk
and places it into a set of buffers, while the consumer sends out the data in the buffers to the users. We develop for the
producer a buffer-inventory-based dynamic scheduling (BIDS) algorithm that guarantees non-zero inventory and non-overflow
of data in the buffers to meet the continuity requirement and no-loss of data for each media stream. The algorithm can deal
with heterogeneous me dia streams as well as the transient circumstances upon service completions and arrivals of new requests.
To smooth out the impact of bursty data of variable-bit-rate media streams and therefore increase the maximum admissible load
of requests, we also introduce into the scheduling scheme a time-scale-dependent peak consumption rate and a virtual cycle
time. Based on BIDS, an effective admission control mechanism can be easily established by checking two simple conditions
respectively on the overall system load and buffer size. Our algorithm is very easy to implement. Experiments carried out
with an actual disk system and real video stream data verify that it is more robust compared to static scheduling algorithms
previously proposed in the literature, especially when handling variable-bit-rate media streams. 相似文献
11.
Zhong Fan 《Computer Communications》2009,32(5):954-960
The new ECMA-368 MAC for UWB WPANs consists of two channel access methods: the distributed reservation protocol (DRP) and prioritized contention access (PCA). The exact method of medium access slot (MAS) allocation in DRP is not specified in the standard. The contribution of this paper is twofold. First, the paper describes a distributed resource allocation method in which a number of interference–avoidance rules are used to reserve slots for devices. Devices maintain sending and receiving tables to track activities in the neighbourhood. The proposed method is a simple, effective solution to the DRP MAS allocation problem, avoiding reservation conflicts and interference from hidden terminals. Secondly, for VBR MPEG-4 video traffic, we propose a bandwidth requirement calculation method based on traffic prediction. In the proposed scheme bandwidth is allocated based on accurate traffic predictions, therefore matching network resources to the traffic demand. Application QoS is maintained while network utilization is kept high. Furthermore, the simple, adaptive linear predictor does not incur much computation overhead. Simulation results have demonstrated the accuracy of the proposed prediction algorithm and effectiveness of the bandwidth allocation method. 相似文献
12.
《Computer Communications》1999,22(15-16):1382-1391
To guarantee quality of service (QoS) in future integrated service networks, traffic sources must be characterized to capture the traffic characteristics relevant to network performance. Recent studies reveal that multimedia traffic shows burstiness over multiple time scales and long range dependence (LRD). While researchers agree on the importance of traffic correlation, there is no agreement on how much correlation should be incorporated into a traffic model for performance estimation and dimensioning of networks.In this article, we present an approach for defining a relevant time scale for the characterization of VBR video traffic in the sense of queueing delay. We first consider the Reich formula and characterize traffic by the Piecewise Linear Arrival Envelope Function (PLAEF). We then define the cutoff interval above which the correlation does not affect the queue buildup. The cutoff interval is the upper bound of the time scale which is required for the estimation of queue size and thus the characterization of VBR video traffic. We also give a procedure to approximate the empirical PLAEF with a concave function; this significantly simplifies the calculation in the estimation of the cutoff interval and delay bound with little estimation loss.We quantify the relationship between the time scale in the correlation of video traffic and the queue buildup using a set of experiments with traces of MPEG/JPEG-compressed video. We show that the critical interval, i.e. the range for the correlation relevant to the queueing delay, depends on the traffic load: as the traffic load increases, the range of the time scale required for estimation for queueing delay also increases. These results offer further insights into the implication of LRD in VBR video traffic. 相似文献
13.
In a video-on-demand (VOD) environment, batching requests for the same video to share a common video stream can lead to significant
improvement in throughput. Using the wait tolerance characteristic that is commonly observed in viewers behavior, we introduce a new paradigm for scheduling in VOD systems.
We propose and analyze two classes of scheduling schemes: the Max_Batch and Min_Idle schemes that provide two alternative
ways for using a given stream capacity for effective batching. In making a video selection, the proposed schemes take into
consideration the next stream completion time, as well as the viewer wait tolerance. We compared the proposed schemes with
the two previously studied schemes: (1) first-come-first-served (FCFS) that schedules the video with the longest waiting request
and (2) the maximum queue length (MQL) scheme that selects the video with the maximum number of waiting requests. We show
through simulations that the proposed schemes substantially outperform FCFS and MQL in reducing the viewer turn-away probability,
while maintaining a small average response time. In terms of system resources, we show that, by exploiting the viewers wait
tolerance, the proposed schemes can significantly reduce the server capacity required for achieving a given level of throughput
and turn-away probability as compared to the FCFS and MQL. Furthermore, our study shows that an aggressive use of the viewer
wait tolerance for batching may not yield the best strategy, and that other factors, such as the resulting response time,
fairness, and loss of viewers, should be taken into account. 相似文献
14.
Guarantees of services in a networked environment are provided by the proper allocation and scheduling of network and system resources. A lot of research in packet scheduling, QoS routing, traffic multiplexing, etc. has been aimed at providing deterministic or statistical service guarantees, while utilizing resources efficiently. In this paper, we propose a resource reservation scheme for a class of multimedia presentations. We characterize this class of multimedia presentations as synchronized distributed multimedia sessions, which we believe are important components of many multimedia applications. In addition to multimedia presentations, the reservation scheme applies to applications with synchronized resource requirements. Based on resource inquiry and interval analysis, the scheme is also able to find feasible resource allocation schedules for resource reservation requests. Built upon a layer of resource abstraction, the scheme suits well with today's heterogeneous network environment. 相似文献
15.
Video sequences are major sources of traffic for broadband ISDN networks, and video compression is fundamental to the efficient
use of such networks. We present a novel neural method to achieve real-time adaptive compression of video. This tends to maintain
a target quality of the decompressed image specified by the user. The method uses a set of compression/decompression neural
networks of different levels of compression, as well as a simple motion-detection procedure. We describe the method and present
experimental data concerning its performance and traffic characteristics with real video sequences. The impact of this compression
method on ATM-cell traffic is also investigated and measurement data are provided. 相似文献
16.
Multimedia streams such as audio and video impose tight temporal constraints for their presentation. Often, related multimedia
streams, such as audio and video, must be presented in a synchronized way. We introduce a novel scheme to ensure the continuous
and synchronous delivery of distributed stored multimedia streams across a communications network. We propose a new protocol for synchronized playback and compute the buffer
required to achieve both, the continuity within a single substream and the synchronization between related substreams. The
scheme is very general and does not require synchronized clocks. Using a resynchronization protocol based on buffer level
control, the scheme is able to cope with server drop-outs and clock drift. The synchronization scheme has been implemented
and the paper concludes with our experimental results. 相似文献
17.
A joint rate control algorithm for variable bit rate (VBR) MPEG-compressed digital video on point-to-point permanent virtual
circuit (PVC) ATM links is proposed. The algorithm controls the encoding mode of a number of video encoders that operate either
on VBR or constant bit rate (CBR) mode. The algorithm selects the encoding mode based on the buffer occupancy of a multiplexer
co-located with the encoders that interfaces them to the PVC link. VBR encoding is the predominant encoding mode used during
congestion-free periods. CBR mode is used only during congested periods. When CBR is selected, new bit rates are jointly assigned
to the encoders based on their relative encoding complexities. The bit rate assigned to the encoders are enforced by a CBR
rate control local to each encoder. The performance of the joint rate control algorithm is evaluated through simulation of
a packet multiplexer, where a number of connections are multiplexed onto a fixed-capacity channel. The performance is compared
to that of multiplexing conventional CBR and open-loop VBR from the video quality and bandwidth efficiency points of view.
Simulation results show that the proposed algorithm improves performance over multiplexed conventional CBR or open-loop VBR
MPEG video, without significantly increasing implementation complexity. The application of the algorithm to video-on-demand
over ATM is discussed. 相似文献
18.
Edward W. Knightly 《Multimedia Systems》1999,7(6):477-485
In order for networks to support the delay and loss requirements of interactive multimedia applications, resource management
algorithms are needed that efficiently allocate network resources. In this paper, we introduce a new resource allocation scheme
based on rate variance envelopes. Such envelopes capture a flow's burstiness properties and autocorrelation structure by characterizing
the variance of its rate distribution over intervals of different length. From this traffic characterization, we develop a
simple and efficient resource allocation algorithm for static priority schedulers by employing a Gaussian approximation over
intervals and considering a maximal busy period. Our approach supports heterogeneous quality-of-service requirements via our
consideration of prioritized service disciplines, and supports heterogeneous and bursty traffic flows via our general framework
of traffic envelopes. To evaluate the scheme, we perform trace-driven simulation experiments with long traces of compressed
video and show that our approach is accurate enough to capture most of the available statistical multiplexing gain, achieving
average network utilizations of up to 90% for these traces and substantially outperforming alternate schemes. 相似文献
19.
We consider streaming of video sequences over both constant and variable bit-rate (VBR) channels. Our goal is to enable decoding of each video unit before exceeding its displaying deadline and, hence, to guarantee successful sequence presentation even if the media rate does not match the channel rate. In this work, we show that the separation between a delay jitter buffer and a decoder buffer is in general suboptimal for VBR video transmitted over VBR channels. We specify the minimum initial delay and the minimum required buffer for a given video stream and a deterministic VBR channel. In addition, we provide some probabilistic statements in case that we observe a random behavior of the channel bit rate. A specific example tailored to wireless video streaming is discussed in greater detail and bounds are derived which allow guaranteeing a certain quality-of-service even for random VBR channels in a wireless environment. Simulation results validate the findings. 相似文献
20.
The broadband integrated services digital networks (B-ISDN) based on asynchronous transfer mode (ATM) technology can support
a wide range of applications such as voice, video, still images, and data. Compression techniques increase the effective bandwidth
utilization, but the bursty and asynchronous nature of the traffic can still lead to congestion in the network, and degradation
of image quality and quality of service (QOS). Some of the features to provide better coding schemes for ATM networks are
layered coding, resynchronization, buffering, interleaved schemes, constrained bit rate due to buffers, encapsulation with
the RTP or AAL1 for clock recovery, lapped transforms, motion compensation, and optimal bit allocation for coders based on
wavelet transforms. We review various techniques forimage and video coding such as transforms, motion compensation, vector
quantization, and subband coding. We outline the impact of the cell loss ratio (CLR), delay and cell delay variation (CDV)
on video coding: blocking effects, loss of frame synchronization, motion vectors, and vector quantization codewords. The open
problems include tuning coding parameters to the available QOS provided by the network. 相似文献