Streaming of scalable h.264 videos over the Internet

To investigate the benefits of scalable codecs in the case of rate adaptation problem, a streaming system for scalable H.264 videos has been implemented. The system considers congestion level in the network and buffer status at the client during adaptation process. The rate adaptation algorithm is content adaptive. It selects an appropriate substream from the video file by taking into account the motion dynamics of video. The performance of the system has been tested under congestion-free and congestion scenarios. The performance results indicate that the system reacts to congestion properly and can be used for Internet video streaming where losses occur unpredictably.

Towards efficient data distribution on computational desktop grids with BitTorrent

Datacentric applications are still a challenging issue for large-scale distributed computing systems. The emergence of new protocols and software for collaborative content distribution over the Internet offers a new opportunity for efficient and fast delivery of a high volume of data. This paper presents an evaluation of the BitTorrent protocol for computational desktop grids. We first present a prototype of a generic subsystem dedicated to data management and designed to serve as a building block for any desktop grid system. Based on this prototype we conduct experiments to evaluate the potential of BitTorrent compared to a classical approach based on FTP data server. The preliminary results obtained with a 65-node cluster measure the basic characteristics of BitTorrent in terms of latency and bandwidth and evaluate the scalability of BitTorrent for the delivery of large input files. Moreover, we show that BitTorrent has a considerable latency overhead compared to FTP but clearly outperforms FTP when distributing large files or files to a high number of nodes. Tests on a synthetic application show that BitTorrent significantly increases the communication/computation ratio of the applications eligible to run on a desktop grid system.     

BitTorrent packet traffic features over IPv6 and IPv4

At present, BitTorrent protocol packets constitute a large part of peer-to-peer application traffic on the Internet. Due to the increasing amount of BitTorrent traffic, it has become inevitable to take into account its effects on network management. Generally, studies on BitTorrent traffic measurement have involved analysis with packets transmitted via IPv4 protocol. However, with several facilities provided by IPv6 protocol, its traffic volume in operational networks is increasing day by day. New features of IPv6 enhance packet processing speeds over routers, switches and end systems. We consider that traffic features and packet traffic characteristics are likely to be affected with increasing amount of IPv6 protocol traffic. Therefore, it becomes significant to explore IPv6 packet traffic characteristics and application traffic features over IPv6. In this study, we investigate the IPv6 BitTorrent packet traffic characteristics in terms of autocorrelation, power spectral density and self similarity of packet size and packet interarrival time. We also perform distribution modeling for IPv4 and IPv6 BitTorrent packet traffic. With these models, efficient packet traffic traces are generated for network simulation studies. A detailed comparison is performed to determine differences between IPv4 and IPv6 BitTorrent packet traffic.     

Clair:一种基于P2P的BitTorrent关键词检索系统

P2P技术是近年学术界和工业界关注的焦点。BitTorrent(以下简称BT)作为一个P2P文件共享系统,用户量不断增长,已逐渐成为网络带宽的主要消耗者之一。BT用户必须到各个发布站点上查找种子文件,致使用户查询的效率比较低。为此,论文提出了基于对等网络的针对BT关键词检索系统Clair,该系统能够高效采集网页上存在的“元信息”文件,快速索引文本以及索引的均匀切分,同时通过针对性的相关性排序算法,给予用户较好的查询结果。实验结果表明,Clair系统具有较好的综合性能。     

Contextualized videos: combining videos with environment models to support situational understanding

Multiple spatially-related videos are increasingly used in security, communication, and other applications. Since it can be difficult to understand the spatial relationships between multiple videos in complex environments (e.g. to predict a person's path through a building), some visualization techniques, such as video texture projection, have been used to aid spatial understanding. In this paper, we identify and begin to characterize an overall class of visualization techniques that combine video with 3D spatial context. This set of techniques, which we call contextualized videos, forms a design palette which must be well understood so that designers can select and use appropriate techniques that address the requirements of particular spatial video tasks. In this paper, we first identify user tasks in video surveillance that are likely to benefit from contextualized videos and discuss the video, model, and navigation related dimensions of the contextualized video design space. We then describe our contextualized video testbed which allows us to explore this design space and compose various video visualizations for evaluation. Finally, we describe the results of our process to identify promising design patterns through user selection of visualization features from the design space, followed by user interviews.     

Cluster Kernels: Resource-Aware Kernel Density Estimators over Streaming Data

A variety of real-world applications heavily relies on an adequate analysis of transient data streams. Due to the rigid processing requirements of data streams, common analysis techniques as known from data mining are not directly applicable. A fundamental building block of many data mining and analysis approaches is density estimation. It provides a well-defined estimation of a continuous data distribution, a fact, which makes its adaptation to data streams desirable. A convenient method for density estimation utilizes kernels. The computational complexity of kernel density estimation, however, renders its application to data streams impossible. In this paper, we tackle this problem and propose our Cluster Kernel approach which provides continuously computed kernel density estimators over streaming data. Not only do Cluster Kernels meet the rigid processing requirements of data streams, they also allocate only a constant amount of memory, even with the opportunity to adapt it dynamically to changing system resources. For this purpose, we develop an intelligent merge scheme for Cluster Kernels and utilize continuously collected local statistics to resample already processed data. We focus on Cluster Kernels for one-dimensional data streams, but also address the multi-dimensional case. We validate the efficacy of Cluster Kernels for a variety of real-world data streams in an extensive experimental study.     

网络视频实验平台的设计与实现

流媒体已经成为下一步网络应用的重要发展方向,对其相关技术进行研究在理论上和实践上都具有重要的意义。该论文的主要工作在于构建了一个通用的网络视频播放系统,它涵盖了端到端网络视频系统的主要技术环节(包括视频的码率控制、传输、解码和播放),支持单播和组播,从而为下一步的研究工作提供了一个优越的实验平台。     

EMCOS: Energy-efficient Mechanism for Multimedia Streaming over Cognitive Radio Sensor Networks

One of the major challenges for multimedia transmission over multimedia WSN (MWSN) in urban environment is the scarcity of spectrum combined with high radio interference. Such environment makes it difficult to ensure high bandwidth, low delay and low packet losses required for real time multimedia streaming applications. We target a scenario of video surveillance in urban environment which not only requires efficiency of spectrum utilization, but also requires energy efficient mechanisms for the battery operated MWSN nodes. In this paper, we propose a new solution for multimedia transmission over WSNs which uses cognitive radio technology for spectrum efficiency and clustering mechanism for energy efficiency. A video streaming solution is proposed that is called “EMCOS: Energy-efficient Mechanism for Multimedia Streaming over Cognitive Radio Sensor Networks”. EMCOS ensures high quality real time multimedia transmission from one or more sources to a given sink, under different spectrum availability conditions, while efficiently using the energy of the MWSN nodes. First, EMCOS clusters the MWSN nodes into different clusters in order to ensure low energy consumption. Additionally for clustering, EMCOS not only takes into consideration the geographic positions, but it also takes into account the actual and the forecast of the channel availability in order to ensure stable clusters. Once the clusters are built, a cluster head is elected for each cluster in a way which preserves the cluster energy by considering the energy utilization of all cluster members. Further, to ensure the content delivery from the source to the sink, a routing/channel selection mechanism is proposed. The channel selection is based on PU activity forecasts to prevent frequent channel switching. Simulations show that our proposal EMCOS outperforms the two existing pioneering mechanisms called SEARCH and SCEEM. EMCOS outperforms them in terms of providing higher video quality, lower end-to-end transmission delay and lower frame loss ratio under varied spectrum conditions.     

无线信道视频流编码与自适应传输方案

由于无线信道的时变特性和移动设备有限的能量资源,保证无线网络视频流传输的Qos是一项比较困难的任务。文章提出了一种基于无线网络的视频流自适应传输架构。这个架构不仅动态的估计了无线网络的状态进行自适应传输,而且同时执了差错控制和功率控制。通过分析网络的状态和视频流的特性来动态分配资源,提高了端到端的QoS。     

一种在数据流上有效执行XQuery查询机制的研究与分析

通过水平积聚和垂直积聚对原始数据流所对应的数据流图进行裁剪,从而将大部分查询转换成一遍遍历数据流便可执行。本文分析在几种特定情况下,数据流图不能被裁剪成经一遍遍历之后就可以被执行的情况。     

Modeling and verification of real-time embedded systems with urgency

Real-time embedded systems are often designed with different types of urgencies such as delayable or eager, that are modeled by several urgency variants of the timed automata model. However, most model checkers do not support such urgency semantics, except for the IF toolset that model checks timed automata with urgency against observers. This work proposes an Urgent Timed Automata (UTA) model with zone-based urgency semantics that gives the same model checking results as absolute urgency semantics of other existing urgency variants of the timed automata model, including timed automata with deadlines and timed automata with urgent transitions. A necessary and sufficient condition, called complete urgency, is formulated and proved for avoiding zone partitioning so that the system state graphs are simpler and model checking is faster. A novel zone capping method is proposed that is time-reactive, preserves complete urgency, satisfies all deadlines, and does not need zone partitioning. The proposed verification methods were implemented in the SGM CTL model checker and applied to real-time and embedded systems. Several experiments, comparing the state space sizes produced by SGM with that by the IF toolset, show that SGM produces much smaller state-spaces.     

rStream: Resilient and Optimal Peer-to-Peer Streaming with Rateless Codes

Due to the lack of stability and reliability in peer-to-peer networks, multimedia streaming over peer-to-peer networks represents several fundamental engineering challenges. First, multimedia streaming sessions need to be resilient to volatile network dynamics and node departures that are characteristic in peer-to-peer networks. Second, they need to take full advantage of the existing bandwidth capacities by minimizing the delivery of redundant content and the need for content reconciliation among peers during streaming. Finally, streaming peers need to be optimally selected to construct high-quality streaming topologies so that end-to-end latencies are taken into consideration. The original contributions of this paper are twofold. First, we propose to use a recent coding technique, referred to as rateless codes, to code the multimedia bitstreams before they are transmitted over peer-to-peer links. The use of rateless codes eliminates the requirements of content reconciliation, as well as the risks of delivering redundant content over the network. Rateless codes also help the streaming sessions to adapt to volatile network dynamics. Second, we minimize end-to-end latencies in streaming sessions by optimizing toward a latency-related objective in a linear optimization problem, the solution to which can be efficiently derived in a decentralized and iterative fashion. The validity and effectiveness of our new contributions are demonstrated in extensive experiments in emulated realistic peer-to-peer environments with our rStream implementation.     

SHIATSU: tagging and retrieving videos without worries

The dramatic growth of video content over modern media channels (such as the Internet and mobile phone platforms) directs the interest of media broadcasters towards the topics of video retrieval and content browsing. Several video retrieval systems benefit from the use of semantic indexing based on content, since it allows an intuitive categorization of videos. However, indexing is usually performed through manual annotation, thus introducing potential problems such as ambiguity, lack of information, and non-relevance of index terms. In this paper, we present SHIATSU, a complete system for video retrieval which is based on the (semi-)automatic hierarchical semantic annotation of videos exploiting the analysis of visual content; videos can then be searched by means of attached tags and/or visual features. We experimentally evaluate the performance of SHIATSU on two different real video benchmarks, proving its accuracy and efficiency.     

Revisiting free riding and the Tit-for-Tat in BitTorrent: A measurement study

In this paper we report new results of our continuous effort on analyzing the impact of incentive mechanisms on user behavior in BitTorrent. In this second measurement and analysis study we find that free riders’ population has significantly increased comparing to our previous measurement study. We relate this increase to the advance in end-users’ connection speeds and to users’ increased knowledge in BitTorrent. We also categorize free riders based on the behavior they exhibit in multiple-torrent system into three types: cheaters, strategic and lucky peers. Furthermore, refuting the findings of other studies, we show that peers who exploit the system in BitTorrent are both high bandwidth capacity peers and low bandwidth capacity peers. Moreover, we argue that the Tit-for-Tat mechanism does not discriminate peers based on their bandwidth capacities and that it reacts successfully against inter-class bandwidth capacity strategic peers. Finally, we propose a memory-backoff approach to the optimistic unchoke policy that reduces the volume of free riding in BitTorrent.

Video streaming distribution over mobile Internet: a survey

In recent times, mobile Internet has witnessed the explosive growth of video applications, embracing user-generated content, Internet Protocol television (IPTV), live streaming, video-on-demand, video conferencing, and FaceTime-like video communications. The exponential rise of video traffic and dynamic user behaviors have proved to be a major challenge to video resource sharing and delivery in the mobile environment. In this article, we present a survey of state-of-the-art video distribution solutions over the Internet. We first discuss the challenges of mobile peer-to-peer (MP2P)-based solutions and categorize them into two groups. We discuss the design idea, characteristics, and drawbacks of solutions in each group.We also give a reviewfor solutions of video transmission in wireless heterogeneous networks. Furthermore, we summarize the information-centric networking (ICN)-based video solutions in terms of in-network caching and name-based routing. Finally, we outline the open issues for mobile video systems that require further studies.     

共享充电桩下负荷时间分布均衡的小区电动汽车充电方案优化

针对电动汽车充电负荷增加、电网安全性降低,以及停车困难小区只能使用共享充电桩等问题,提出了一种充电桩选择与电动汽车充电优化的组合模型。该模型以共享充电桩之间充电时间标准差和全天充电负荷标准差之和最小为目标。考虑到电动汽车充电桩分配方案以及电动汽车充电方案两者的重要程度并不相同,提出了一种随着迭代次数的增加,变化概率不断改变的动态概率遗传算法。将改进后的遗传算法求解该模型,通过求解一个算例,进一步阐述所提算法的原理和过程,验证了该算法的可行性和有效性。     

Segmenting with style: detecting program and story boundaries in TV news broadcast videos

Multimedia Tools and Applications - Television news is an important medium to convey information to masses. This motivates several stakeholders to monitor and analyze the news broadcasts....     

WuKong: a practical video streaming service based on native BitTorrent and scalable video coding

Many researches on peer-to-peer video streaming have focused on dealing with highly dynamic, high-churn P2P environment. Most of P2P streaming protocols were modified from a P2P file sharing protocol. Inspired by the high performance on peer-to-peer file sharing of BitTorrent, we propose an overlaying streaming mechanism on the native BitTorrent protocol and realize a practical P2P video streaming service, called WuKong. WuKong not only takes advantages of BitTorrent but also combines the video scalability of layered video coding. In this paper, we depict an overlaid streaming mechanism in WuKong and an adaptive layer-downloading process to balance between the video quality and bandwidth utilization on heterogeneous peers. WuKong is carried out by using an open-sourced library of the BitTorrent protocol, coding schemes of the Windows Media Video (WMV), and the Scalable Video Coding (SVC). We measured and compared the service quality of end-users served by WuKong on heterogeneous peers. In addition, we evaluated the effectiveness of WuKong with peers that are randomly joining and leaving the P2P network. The results show that WuKong not only provides high quality P2P video streaming services but also supports different scaling abilities over heterogeneous devices.