An adaptive video multicast scheme for varying workloads

Periodic broadcast and scheduled multicast have been shown to be very effective in reducing the demand on server bandwidth. While periodic broadcast is better for popular videos, scheduled multicast is more suitable for less popular ones. Work has also been done to show that a hybrid of these techniques offer the best performance. Existing hybrid schemes, however, assume that the characteristic of the workload does not change with time. This assumption is not true for many applications, such as movie on demand, digital video libraries, or electronic commerce. In this paper, we show that existing scheduled multicast techniques are not suited for hybrid designs. To address this issue, we propose a new approach and use it to design an adaptive hybrid strategy. Our technique adjusts itself to cope with a changing workload. We provide simulation results to demonstrate that the proposed technique is significantly better than the best static approach in terms of service latency, throughput, defection rate, and unfairness.     

A General Framework of Time-Variant Bandwidth Allocation in the Data Broadcasting Environment

Data broadcast is an advanced technique to realize large scalability and bandwidth utilization in a mobile computing environment. In this environment, the channel bandwidth of each channel is variant with time in real cases. However, traditional schemes do not consider time-variant bandwidth of each channel to schedule data items. Therefore, the above drawback degrades the performance in generating broadcast programs. In this paper, we address the problem of generating a broadcast program to disseminate data via multiple channels of time-variant bandwidth. In view of the characteristics of time-variant bandwidth, we propose an algorithm using adaptive allocation on time-variant bandwidth to generate the broadcast program to avoid the above drawback to minimize average waiting time. Experimental results show that our approach is able to generate the broadcast programs with high quality and is very efficient in a data broadcasting environment with the time-variant bandwidth.     

基于蓝牙的连续媒体实时传输技术的研究

由于蓝牙无线信道带宽较窄且动态变化，在其上实时传输连续媒体数据是一个巨大挑战．本文研究了其中若干关键技术．包括蓝牙通信技术、视频／音频压缩技术和自适应服务质量控制技术等．文中提出了一种基于简单网络管理协议(SNMP)的自适应服务质量控制方案．设计了蓝牙多媒体传输管理信息库(简称BMT—MIB)，通过动态监测当前蓝牙无线信道和终端系统状态，有效利用带宽等资源．文中还给出了基于蓝牙的远程监控系统原型的设计和实现。     

端到端MPEG-4 FGS视频TCP友好的平滑传输

着重研究了Internet上MPEG-4 FGS(fine grained scalable)视频流的自适应平滑传输,其主要目的在于,在网络带宽变化的情况下,提供稳定的视频回放质量.提出了一种新的基于TFRC(TCP-friendly rate control)的MPEG-4 FGS端到端视频流传输系统框架,在此框架的基础上,首先假设完整的可用带宽变化已知,并且提出了一种离线的自适应平滑算法.此后,给出一种基于改进的ARAR(autoregressive autoregressive)预测技术的在线自适应平滑算法.最后,以NS-2为实验平台进行了模拟实验.模拟实验表明,提出的离线和在线自适应平滑算法可以充分利用可用网络带宽,并且能够在可用网络带宽持续波动的情况下保证接收方的回放尽可能地平稳,从而达到获得最佳视觉效果的目的.     

An adaptive and opportunistic broadcast protocol for vehicular ad hoc networks

A primary goal of broadcasting in vehicular ad hoc network (VANET) is to improve the road safety by transmitting alert messages to all surrounding vehicles as soon as possible. In this paper, we adopt the concept of opportunistic routing and propose a multiple candidate relays opportunistic broadcast (MCROB) protocol for VANET. The MCROB protocol is a sender-driven broadcast scheme independent of node density. The packet delivery ratio (PDR) is derived and an expected transmission speed (ETS) for the MCROB is proposed. A priority rule for selecting a proper candidate relay and an adaptive algorithm for forwarding timers of candidate relays are also presented in this paper. Simulations show that MCROB is adaptive to the rapid changing of network conditions. It keeps a low communication overhead introduced by the broadcast and increases the average transmission speed by around 40%.     

多媒体文件服务器的磁盘带宽分配策略

讨论多媒体文件服务器磁盘I/O带宽的分配策略问题,提出一种根据不同应用请求的负载变化情况对服务器磁盘带宽进行自适应分配的算法。该算法由负载检测模块、带宽管理模块组成,提高了多媒体文件服务器的易管理性,在短暂的过载情况下保持了服务器的稳定性,为更多的软实时请求提供服务。     

Node scheduling problem in underwater acoustic sensor network using genetic algorithm

Underwater acoustic sensor network (UWASN) has recently aroused the interest of researchers and scientists in this field. The acoustic sensor bandwidth is limited in underwater and it causes low successful packet transmission. One of the methods to overcome this handicap is efficient broadcast scheduling of underwater acoustic sensor node (UASN) that would help in transmitting and receiving data without any collision. This can be done with the help of time division multiple access (TDMA). The basic idea is to address broadcast scheduling problem in UWASN for utilizing the limited available bandwidth by parallelizing the node transmission such that it does not interfere with each other in same time slot; it also minimizes the node turnaround transmission time in the network by optimizing the time slots in TDMA frame. The objective of this paper is to maximize the utilization of the available underwater acoustic bandwidth and to achieve high throughput as well as to reduce the node turnaround wait time by using an evolutionary genetic algorithm (GA). The simulation results prove that every node in the UWASN transmits in an average minimal turnaround time by minimizing the time slots and maximizing the throughput in the network by scheduling the possible nodes with parallel transmission.     

A speculative load adaptive streaming scheme for efficient video delivery

Video on demand services require video broadcast schemes to provide efficient and reliable performance under various client request loads. In this paper, we have developed an efficient request load adaptive broadcast scheme, speculative load adaptive streaming scheme (SLAS), that requires lower service bandwidth than previous approaches, regardless of request rate. We have provided both analysis and simulation to show the performance gain over previous schemes. In this paper, we provide the theoretic upper bound of the continuous segment allocations on channels. We found that the number of allocated segments of the SLAS is close to the theoretic upper bound when compared with other schemes over various numbers of stream channels. Our analysis of client waiting time is almost identical to simulation results about all client requests. By simulation, we compared the required service bandwidth and storage requirements of the SLAS scheme and other schemes and found the SLAS scheme is an efficient broadcast scheme as compared to well known seamless channel transition schemes.     

Adaptive Piggybacking Schemes for Video-On-Demand Systems

A critical issue in the performance of a video-on-demand system is the I/O bandwidth required in order to satisfy client requests. A number of techniques have been proposed in order to reduce these bandwidth requirements. In this paper we concentrate on one such technique, known as adaptive piggybacking. We develop and analyze piggyback merging policies which are optimal over large classes of reasonable methods.     

An enhanced client-centric approach for efficient video broadcast

Periodic broadcast is a cost-effective solution for large-scale distribution of popular videos. Regardless of the number of video requests, this strategy guarantees a constant worst service latency to all clients, making it possible to serve a large community with a minimal amount of broadcast bandwidth. Although many efficient periodic broadcast techniques have been proposed, most of them impose rigid requirements on client receiving bandwidth. They either demand clients to have the same bandwidth as the video server, or limit them to receive no more than two video streams at any one time. In our previous work, we addressed this problem with a Client-Centric Approach (CCA). This scheme takes into consideration both server broadcast bandwidth and client receiving bandwidth and allows clients to use all their receiving capability for prefetching broadcast data. As a result, given a fixed broadcast bandwidth, a shorter broadcast period can be achieved with an improved client communication capability. In this paper, we present an enhanced version of CCA to further leverage client bandwidth for more efficient video broadcast. The new scheme reduces the broadcast latency up to 50% as compared to CCA. We prove the correctness of this new technique and provide an analytical evaluation to show its performance advantage as compared with some existing techniques.

异构环境下层次编码多视频源多共享信道分层组播

视频组播是许多当前和将来网络服务的重要组成部分,如视频会议,远程学习、远地展示及视频点播,随着网络传送基础设施的改善和端系统处理能力的增强,组播视频应用日益变得可行,组播视频传输中存在的主要问题是网络送资源的异构性和动态性,其使得视频流的多个接收方都达到可接受的流量特性变得异常困难,目前该问题的一个有效解决方式就是利用自适应的分层视频传输机制,在该机制中,各源产生层次媒体流,并在多个网络信道中传输。对视频会议类的多点到多点视频组播应用,信道往往被所有潜在的发送方共享,任何发送方都可在任何一个共享信道中发送其视频层次。在该多点到多点、共享信道、分层视频组播模型下,一个关键问题就是如何动态确定各视频源层次到各共享组播信道的映射,映射策略直接影响到会话整体视频接收质量和网络带宽利用率。典型的方式是顺序映射,该映射方式同等对待各发送方,但利用该方式,随源数目的增加,在各共享网络信度上会出现带宽可伸缩性问题,而且顺序映射方式无法适应网络传送资源和会话状态的动态变化。为此,该文设计了一种基于接收方反馈信息的自适应的层次映射算法,接收方周期性地将其当前感兴趣的发送方及接收速率的信息反馈给某控制节点,而控制节点就利用当前反馈信息动态地调整映射策略。经证实,该算法始终能比顺序层次映射算法获得更高的整体视频接收质量,并具有高的带宽利用率和很小的复杂度。     

QoS机制在IPSec安全设备上的分析与实现

提出了在IPSec 安全设备上实施QoS的体系方案。设计了适合IPSec安全设备特点的数据分类规则。为IPSec安全设备构建了一个系统排队理论模型,该模型以延迟作为系统运行目标,以带宽作为分配资源。据此设计了一个自适应带宽分配循环队列调度算法。实际运行的测试结果表明,在重载情况下,实施了QoS的IPSec 安全设备可以为重要业务流提供带宽和时延保障。     

On-demand waypoints for live P2P video broadcasting

A peer-to-peer architecture has emerged as a promising approach to enabling the ubiquitous deployment of live video broadcasting on the Internet. However the performance in these architectures is unpredictable and fundamentally constrained by the characteristics of the members participating in the broadcast. By characteristics, we refer to user dynamics, out-going bandwidth connectivity, whether the member is behind NAT/firewall, and the network conditions among participating members. While several researchers have looked at hybrid P2P/CDN approaches to address these issues, such approaches require provisioning of centralized server resources prior to a broadcast, which complicates the goal of ubiquitous video broadcasting. In this paper, we explore an alternative architecture where users are willing to donate their bandwidth resources to a broadcast event, even though they are not a participant in the event. Such users constitute what we term a waypoint community. Any given broadcast event involves constructing overlays only based on participants to the extent possible, however waypoints may be dynamically invoked in an on-demand, performance-driven fashion to improve the performance of a broadcast. We present the design of a system built on this idea. Detailed results from trace-driven experiments over the PlanetLab distributed infrastructure and Emulab demonstrate the potential of the waypoint architecture to improve the performance of purely P2P-based overlays.     

基于H.264无线视频传输系统的研究

由于无线信道易错、时变和带限的特点,给视频数据的无线传输带来了巨大的挑战。本文设计了一种带育反馈的无线信道视频传输系统,为了加强系统的抗误码性,重点研究了基于错误隐藏的联合信道率失真算法、对原有视频容错编码方法进行改进,并提出了一种基于丢包反馈的自适应数据分割选择模式,在低带宽高误码的无线信道环境下,提高了视频图像的质量。     

实时环境下一种混合广播调度策略

在实时的非对称通讯环境下,自适应混合广播策略能够根据数据的请求模式以及时间限制等特征来动态分配周期广播和按需广播的带宽比例.将这一策略推广到基于事务的多数据项广播调度中,同时引入"分布式广播"思想,以更精细的周期广播粒度来解决过长的周期广播与事务及数据的实时要求之间的矛盾,并且动态分配时间槽.实验结果表明:改进的调度策略更适合于实时环境下的数据广播,具有更低的事务失败率以及更小的上行信道负荷.     

Hierarchical control of multiple resources in distributed real-time and embedded systems

Real-time and embedded systems have traditionally been designed for closed environments where operating conditions, input workloads, and resource availability are known a priori, and are subject to little or no change at runtime. There is increasing demand, however, for adaptive capabilities in distributed real-time and embedded (DRE) systems that execute in open environments where system operational conditions, input workload, and resource availability cannot be characterized accurately a priori. A challenging problem faced by researchers and developers of such systems is devising effective adaptive resource management strategies that can meet end-to-end quality of service (QoS) requirements of applications. To address key resource management challenges of open DRE systems, this paper presents the Hierarchical Distributed Resource-management Architecture (HiDRA), which provides adaptive resource management using control techniques that adapt to workload fluctuations and resource availability for both bandwidth and processor utilization simultaneously. This paper presents three contributions to research in adaptive resource management for DRE systems. First, we describe the structure and functionality of HiDRA. Second, we present an analytical model of HiDRA that formalizes its control-theoretic behavior and presents analytical assurance of system performance. Third, we evaluate the performance of HiDRA via experiments on a representative DRE system that performs real-time distributed target tracking. Our analytical and empirical results indicate that HiDRA yields predictable, stable, and efficient system performance, even in the face of changing workload and resource availability.     

网络自适应传输控制策略研究

针对流媒体传输中的拥塞问题，对网络自适应传输控制进行了研究，结合RTP协议的传输特性，提出了一种基于带宽的网络自适应传输策略并阐述了这种策略的控制机理。该策略能够根据网络资源状况动态调节传输速率、匹配网络带宽，实现了网络自适应传输。     

移动环境中自适应的XML广播索引

针对如何减少移动计算环境中XML数据广播的调谐时间和访问时间的问题,提出一种基于自适应索引的XML广播调度算法XAISA。它能根据系统负荷动态调整数据块的度,从而达到性能最优化。性能分析和实验比较表明,该算法能以极小的平均访问时间的代价大大减少平均调谐时间及接收XML广播数据的时间。     

基于DDR3 SDRAM的高速大容量数据缓存设计

为了满足对高清非压缩视频数据的实时采集要求,解决常用数据缓存因容量小、数据读写速率低等缺点带来的数据丢失问题,提出了一种基于DDR3 SDRAM的高速大容量数据缓存的设计方法;该方法采用了不同时域数据处理技术、高速数据存储技术以及总线优先级仲裁技术,实现了数据速率高达400 Mbytes/s的实时数据的高速缓存;实践证明,该数据缓存可应用于高清非压缩视频数据的实时采集系统中。     

Is it DSS or OLTP: automatically identifying DBMS workloads

The type of the workload on a database management system (DBMS) is a key consideration in tuning the system. Allocations for resources such as main memory can be very different depending on whether the workload type is Online Transaction Processing (OLTP) or Decision Support System (DSS). A DBMS also typically experiences changes in the type of workload it handles during its normal processing cycle. Database administrators must therefore recognize the significant shifts of workload type that demand reconfiguring the system in order to maintain acceptable levels of performance. We envision intelligent, autonomic DBMSs that have the capability to manage their own performance by automatically recognizing the workload type and then reconfiguring their resources accordingly. In this paper, we present an approach to automatically identifying a DBMS workload as either OLTP or DSS. Using data mining techniques, we build a classification model based on the most significant workload characteristics that differentiate OLTP from DSS and then use the model to identify any change in the workload type. We construct and compare classifiers built from two different sets of workloads, namely the TPC-C and TPC-H benchmarks and the Browsing and Ordering profiles from the TPC-W benchmark. We demonstrate the feasibility and success of these classifiers with TPC-generated workloads and with industry-supplied workloads.