Segment‐aware dynamic routing for DASH flows over software‐defined networks

Most of the video streaming applications running over the Internet send video data over HTTP and provide an architecture for video clients to adapt video quality during streaming. In HTTP adaptive streaming, a raw video is encoded at various qualities, each encoded video file is divided into small segments, and the clients may change the segment quality by sending requests for segments having different qualities over time. MPEG has standardized dynamic adaptive streaming over HTTP (MPEG‐DASH) due to this tendency. In this work, we focus on DASH over software‐defined networks (SDN), and we dynamically reroute DASH flows by considering the current network capacity, available bandwidth of the paths, and bitrate of the segments in order to provide high quality of experience (QoE) and fairness among DASH clients. Simulations performed under various network conditions show that the proposed study provides higher QoE and fairness compared with the max‐flow routing approach.     

Eliminating bandwidth estimation from adaptive video streaming in wireless networks

Dynamic Adaptive Streaming over HTTP (DASH) is the state-of-the-art technology for video streaming and has been widely deployed in both wired and wireless environments. However, mobile DASH users often suffer from video quality oscillation and even video freeze in wireless environments, which results in poor user experience. This is mainly because most quality adaptation algorithms in DASH rely highly on bandwidth estimation to adjust the video quality while wireless network bandwidth is unstable in nature and changes frequently according to wireless channel contention and condition. To provide stable performance, even during severe bandwidth fluctuation, this paper proposes the Wireless Quality Adaptation (WQUAD) algorithm, which eliminates bandwidth estimation from quality adaptation. Thanks to the Scalable Video Codec (SVC), the proposed scheme always prioritizes to lower layers over higher ones as long as the play-out buffer is not completely filled by the lower layers. As a result, the client always fills the buffer with the base layers first and then the upper enhancement layers sequentially. This horizontal adaptation is straightforward and does not require any bandwidth estimation. Through NS-2 simulations, we show that WQUAD achieves (i) stable performance, keeping the video quality level with respect to the long-term network bandwidth, (ii) effective video freeze prevention, and (iii) high video quality on average.     

QoE optimization for HTTP adaptive streaming: Performance evaluation of MEC-assisted and client-based methods

Seamless streaming of high quality video under unstable network condition is a big challenge. HTTP adaptive streaming (HAS) provides a solution that adapts the video quality according to the network conditions. Traditionally, HAS algorithm runs at the client side while the clients are unaware of bottlenecks in the radio channel and competing clients. The traditional adaptation strategies do not explicitly coordinate between the clients, servers, and cellular networks. The lack of coordination has been shown to lead to suboptimal user experience. As a response, multi-access edge computing (MEC)-assisted adaptation techniques emerged to take advantage of computing and content storage capabilities in mobile networks. In this study, we investigate the performance of both MEC-assisted and client-side adaptation methods in a multi-client cellular environment. Evaluation and comparison are performed in terms of not only the video rate and dynamics of the playback buffer but also the fairness and bandwidth utilization. We conduct extensive experiments to evaluate the algorithms under varying client, server, dataset, and network settings. Results demonstrate that the MEC-assisted algorithms improve fairness and bandwidth utilization compared to the client-based algorithms for most settings. They also reveal that the buffer-based algorithms achieve significant quality of experience; however, these algorithms perform poorly compared with throughput-based algorithms in protecting the playback buffer under rapidly varying bandwidth fluctuations. In addition, we observe that the preparation of the representation sets affects the performance of the algorithms, as does the playback buffer size and segment duration. Finally, we provide suggestions based on the behaviors of the algorithms in a multi-client environment.     

A novel adaptive logic for dynamic adaptive streaming over HTTP

In this paper, we propose an estimation method that estimates the throughput of upcoming video segments based on variations in the network throughput observed during the download of previous video segments. Then, we propose a rate-adaptive algorithm for Hypertext Transfer Protocol (HTTP) streaming. The proposed algorithm selects the quality of the video based on the estimated throughput and playback buffer occupancy. The proposed method selects high-quality video segments, while minimizing video quality changes and the risk of playback interruption, improving user’s experience. We evaluate the algorithm for single- and multi-user environments and demonstrate that it performs remarkably well under varying network conditions. Furthermore, we determine that it efficiently utilizes network resources to achieve a high video rate; competing HTTP clients achieve equitable video rates. We also confirm that variations in the playback buffer size and segment duration do not affect the performance of the proposed algorithm.     

Instruction fetch architectures and code layout optimizations

The design of higher performance processors has been following two major trends: increasing the pipeline depth to allow faster clock rates, and widening the pipeline to allow parallel execution of more instructions. Designing a higher performance processor implies balancing all the pipeline stages to ensure that overall performance is not dominated by any of them. This means that a faster execution engine also requires a faster fetch engine, to ensure that it is possible to read and decode enough instructions to keep the pipeline full and the functional units busy. This paper explores the challenges faced by the instruction fetch stage for a variety of processor designs, from early pipelined processors, to the more aggressive wide issue superscalars. We describe the different fetch engines proposed in the literature, the performance issues involved, and some of the proposed improvements. We also show how compiler techniques that optimize the layout of the code in memory can be used to improve the fetch performance of the different engines described Overall, we show how instruction fetch has evolved from fetching one instruction every few cycles, to fetching one instruction per cycle, to fetching a full basic block per cycle, to several basic blocks per cycle: the evolution of the mechanism surrounding the instruction cache, and the different compiler optimizations used to better employ these mechanisms     

CDN架构下流媒体代理缓存策略的研究

在流媒体点播系统中,现有的CDN架构下的缓存策略并没有很好地解决骨干网带宽资源浪费的问题。为了降低骨干网带宽、启动延迟及网络负载不平衡及更好地支持点播过程中的VCR操作,本文在CDN的流媒体系统架构基础上,结合原有前缀缓存及分段缓存策略,提出一种新的基于代理服务器及备用代理服务器的缓存策略,以缓解系统对骨干网络带宽的需求,并在理论上有效节约了代理服务器的缓存资源,降低了用户点播的启动延迟。     

OTT传输技术选择分析

对互联网媒体内容传输技术的发展进行了分析,其中重点分析了近期出现的以HTTP为基础的自适应流媒体,包括Microsoft 的Smooth Streaming、Adobe的 HTTP Dynamic Streaming、APPLE的HTTP Live Streaming以及MPEG-DASH.在部分测试数据的基础上,推论出适合有线网络公司的OTT业务传输技术.     

自适应流媒体技术在CDN中的应用研究

内容分发网络(CDN)面临多终端、多业务融合所带来的各种技术挑战,自适应流媒体技术是一种结合了流控和HTTP渐进式下载的分发技术,它能够自动适应网络带宽,为用户提供良好的视频播放体验。论述CDN平台承载自适应流媒体业务所面临的技术挑战,并提出相应的应用解决方案,提高用户的视频服务体验,满足不断发展的视频服务需求。     

Fast NAND Flash Memory System for Instruction Code Execution

The objective of this research is to design a high‐performance NAND flash memory system containing a buffer system. The proposed instruction buffer in the NAND flash memory consists of two parts, that is, a fully associative temporal buffer for temporal locality and a fully associative spatial buffer for spatial locality. A spatial buffer with a large fetching size turns out to be effective for serial instructions, and a temporal buffer with a small fetching size is devised for branch instructions. Simulation shows that the average memory access time of the proposed system is better than that of other buffer systems with four times more space. The average miss ratio is improved by about 70% compared with that of other buffer systems.     

Research on Q-learning based rate control approach for HTTP adaptive streaming

HTTP adaptive streaming (HAS) has become the standard for adaptive video streaming service.In changing network environments,current hardcoded-based rate adaptation algorithm was less flexible,and it is insufficient to consider the quality of experience (QoE).To optimize the QoE of users,a rate control approach based on Q-learning strategy was proposed.the client environments of HTTP adaptive video streaming was modeled and the state transition rule was defined.Three parameters related to QoE were quantified and a novel reward function was constructed.The experiments were employed by the Q-learning rate control approach in two typical HAS algorithms.The experiments show the rate control approach can enhance the stability of rate switching in HAS clients.     

一种基于罚因子的DASH调度算法

随着移动互联网的普及,基于DASH的流媒体传输协议的应用越来越广泛。如何在带宽波动较大的移动互联网环境中保证用户实现流媒体的流畅点播,提高用户的体验度是DASH调度算法最主要研究的问题。以提高用户体验度为出发点,结合带宽和缓存深度两方面因素,对带宽预测模型的置信度进行评价。在高置信度情况下,大胆地对网络带宽估计模型的模型参量进行调整;在低置信度情况下,以保护缓冲区深度为目的,谨慎地对模型参量进行调整。这种调整势必会对QoE造成相应的影响,该影响作为"罚因子"反馈回模型置信度的评价,以获得模型参数的动态最优解,得到一种较好的DASH调度算法。     

Optical polarization bistability in TM wave injected semiconductorlasers

Experimental results of optical polarization bistability in InGaAsP lasers are reported and the causes of polarization switching and nonlinear response in this bistability are discussed. The input light signal consisted of the transverse magnetic (TM) wave, while the semiconductor lasers operated in a fundamental transverse electric (TE) mode when the light input was not injected. The light output versus light input characteristics were dependent on the input wavelength. Switching times of up to a few hundred picoseconds were achieved for both switch-up and switch-down. It was found that the TE and TM outputs originate from the TE oscillation and the TM amplification, respectively. Calculations using the rate equations showed that the TM input induces the nonlinearity of the carrier density. These results indicate that this bistability is a type of dispersive bistability     

Software‐defined network‐based prioritization to avoid video freezes in HTTP adaptive streaming

HTTP adaptive streaming (HAS) is becoming the de facto standard for video streaming services over the Internet. In HAS, each video is segmented and stored in different qualities. Rate adaptation heuristics, deployed at the client, allow the most appropriate quality level to be dynamically requested, based on the current network conditions. It has been shown that state‐of‐the‐art heuristics perform suboptimal when sudden bandwidth drops occur, therefore leading to freezes in the video playout, the main factor influencing users' quality of experience (QoE). This issue is aggravated in case of live events, where the client‐side buffer has to be kept as small as possible in order to reduce the playout delay between the user and the live signal. In this article, we propose a framework capable of increasing the QoE of HAS clients by reducing video freezes. The framework is based on OpenFlow, a widely adopted protocol to implement the software‐defined networking principle. An OpenFlow controller is in charge of introducing prioritized delivery of HAS segments, based on the network conditions and the HAS clients' status. Particularly, the HAS clients' status is obtained without any explicit clients‐to‐controller communication, and thus, no extra signaling is introduced into the network. Moreover, this OpenFlow controller is transparent to the quality decision process of the clients, as it assists the delivery of the segments, but it does not determine the actual quality to be requested. In order to provide a comprehensive analysis of the proposed approach, we investigate the performance of the proposed OpenFlow‐based framework in the presence of realistic Internet cross‐traffic. Particularly, we model two types of applications, namely, HTTP web browsing and progressive download video streaming, which currently represent the majority of Internet traffic together with HAS. By evaluating this novel approach through emulation in several multi‐client scenarios, we show how the proposed approach can reduce freeze time for the HAS clients due to network congestion up to 10 times compared with state‐of‐the‐art heuristics, without impacting the performance of the cross‐traffic applications. Copyright © 2016 John Wiley & Sons, Ltd.     

Analysis of polarization bistability of phase-shifted DFB laser dueto TM light injection

As a method of high-bit-rate optical processing, the TM light injection-induced optical polarization bistability using Fabry-Perot type laser diodes has been experimentally demonstrated and theoretically analyzed. In these studies, although switching times less than 1 ns both for switch-up and switch-down have been reported, both of the TE and TM outputs exhibit longitudinal multimode spectra. In practical processing systems, a dynamically stable operation of the polarization switching is considered to be essential. It is the purpose of this paper to present an analytical study of the TM light injection-induced polarization bistability using a λ/4-shifted distributed feedback (DFB) laser model and to describe the detailed picture of the mechanism     

内容分发网络的研究

随着宽带网络和宽带流媒体应用的兴起,内容分发网络（CDN）作为一种提高网络传输内容,特别是流媒体内容传输的服务质量、节省骨干网络带宽的技术,在国内外得到越来越广泛的应用。CDN是一个建立在不同区域的节点服务器组成的虚拟网络,CDN可以实现把互联网上的内容高效、稳定地发送到离网民最近的地方。这里总结介绍CDN出现的原因,CDN的技术基础及其分层模型,流媒体CDN的性能指标。     

基于三值编码的非正弦时域正交调制方法

在带宽受限的通信系统中,系统的频带利用率是非常重要的性能指标。为了提高非正弦时域正交调制系统的频带利用率,该文提出一种基于三值编码的高效非正弦时域正交调制方法。通过将待调制的二进制数据转换为多路并行的三进制数据,分别与多路正交脉冲的3种发送相位状态对应,增加了每个码元携带的信息量,从而提高系统的频带利用率。给出了系统的调制解调模型,理论推导了系统的频带利用率和误码性能,并与已有的非正弦时域正交调制系统进行了对比分析和仿真。结果表明,基于三值编码的非正弦时域正交调制方法可以有效提高系统的频带利用率,而信噪比的增加不超过0.3 dB。该方法适用于对信息传输速率要求高但带宽受限的场合,也有助于降低系统的实现复杂度。     

内容分发网络关键技术分析

随着宽带网络和宽带流媒体应用的兴起,CDN作为一种提高网络内容,特别是流媒体内容传输的服务质量、节省骨干网络带宽的技术,在国内外得到越来越广泛的应用。本文主要介绍了CDN技术的基本概念、分层模型、关键技术,并对CDN的发展趋势进行了简要分析。     

基于细粒度调整的同步播放控制算法

针对网络时延和时延抖动引起缓存波动而造成的流媒体播放不连续,基于接收端播放速率调整,提出一种播放速率自适应调整的播放缓存控制算法。算法依据缓存区的占用水平,通过构造控制序列,动态、细粒度地调整媒体的播放速率。在校园网环境下的模拟结果表明,该算法能够有效地减少缓存上溢或下溢引起的播放跳跃或停顿,从而实现流媒体的平滑播放。     

一种基于HTTP长连接的自适应流媒体传输系统

提出了一种基于HTTP的自适应流媒体传输系统,一方面,该系统利用了HTTP长连接技术,有效地减少了频繁建立与断开TCP连接带来的网络资源开销;另一方面,该系统采用了一种服务器端驱动的码率自适应控制策略,这种策略不仅有效地适应于网络环境的变化,还降低了对客户端的要求,具有很强的通用性。实验结果表明该系统方案是有效的。     

Performance benchmarking of wireless Web servers

The advent of mobile computers and wireless networks enables the deployment of wireless Web servers and clients in short-lived ad hoc network environments, such as classroom area networks. The purpose of this paper is to benchmark the performance capabilities of wireless Web servers in such an environment. Network traffic measurements are conducted on an in-building IEEE 802.11b wireless ad hoc network, using a wireless-enabled Apache Web server, several wireless clients, and a wireless network traffic analyzer. The experiments focus on the HTTP transaction rate and end-to-end throughput achievable in such an ad hoc network environment, and the impacts of factors such as Web object size, number of clients, and persistent HTTP connections. The results show that the wireless network bottleneck manifests itself in several ways: inefficient HTTP performance, client-side packet losses, server-side packet losses, network thrashing, and unfairness among Web clients. Persistent HTTP connections offer up to 350% improvement in HTTP transaction rate and user-level throughput, while also improving fairness for mobile clients accessing content from a wireless Web server.