Optimal video placement scheme for batching VOD services

Advances in broadband technology are generating an increasing demand for video-on-demand (VOD) applications. In this paper, an optimal video placement scheme is proposed for a batching VOD system with multiple servers. Given a specified requirement of the blocking probability, an optimal batching interval is derived and the corresponding file placement is obtained by hybrid genetic algorithm. It is demonstrated that the specified requirement on blocking probability is satisfied, while both batching interval and server capacity usage are minimized simultaneously.     

Social video caching

We investigate online browsing of interrelated content, represented as a catalog of items of interest featuring graph dependencies. The content is served to clients via a system of decentralized proxy caches connected to cloud servers. A client selects the next item to browse from the list of recommended items, displayed on the currently browsed item׳s catalog page. A cache has a limited size to have every item selected by its browsing clients available for local access. Thus, the system pays a penalty, whenever a client selects an item that cannot be served directly from the proxy. Conversely, the system gains a reward, if a client selects an immediately available item. We aim to select the items to cache that maximize the profit earned by the system, for the given cache capacity. We design two linear-time optimization techniques for finding the desired items to cache. We enhance the operation of the system via two additional strategies. The first one dynamically tracks the items׳ selection probabilities for a client, as a function of its prior catalog access pattern and those of its community peers. The second one constructs dynamic overlays, on behalf of the clients, that are used to share the selected items directly among them. This augments the system׳s serving capacity and enhances the clients׳ browsing experience. We study the performance of the optimization techniques via numerical experiments. They exhibit efficiency gains over reference methods, by exploiting the content dependencies and correlated community-driven access patterns of the clients. We also report proxy bandwidth savings achieved by our overlay strategy over state-of-the-art methods, on content access patterns of clients with Facebook or Twitter ties.     

基于收益感知的信息中心网络缓存机制

针对信息中心网络（ICN）内置缓存系统中的海量内容块流行度获取和存储资源高效利用问题,以最大化节省内容访问总代价为目标,建立针对内容块流行度的缓存收益优化模型,提出了一种基于收益感知的缓存机制。该机制利用缓存对请求流的过滤效应,在最大化单点缓存收益的同时潜在地实现节点间协作和多样化缓存;使用基于布隆过滤器的滑动窗口策略,在检测请求到达间隔时间的同时兼顾从源服务器获取内容的代价,捕获缓存收益高的内容块。分析表明,该方法能够大幅压缩获取内容流行度的存储空间开销;仿真结果表明,该方法能够较为准确地实现基于流行度的缓存收益感知,且在内容流行度动态变化的情况下,在带宽节省和缓存命中率方面更具优势。     

Scheduling and bandwidth allocation for the distribution of archived video in VOD systems

Providing costeffective videoondemand (VOD) services necessitates reducing the required bandwidth for transporting video over highspeed networks. In this paper, we investigate efficient schemes for transporting archived MPEGcoded video over a VOD distribution network. A video stream is characterized by a timevarying traffic envelope, which provides an upper bound on the bit rate. Using such envelopes, we show that video streams can be scheduled for transmission over the network such that the perstream allocated bandwidth is significantly less than the source peak rate. In a previous work [13], we investigated stream scheduling and bandwidth allocation using global traffic envelopes and homogeneous streams. In this paper, we generalize the scheduling scheme in [13] to include the heterogeneous case. We then investigate the allocation problem under windowbased traffic envelopes, which provide tight bounds on the bit rate. Using such envelopes, we introduce three streamscheduling schemes for multiplexing video connections at a server. The performance of these schemes is evaluated under static and dynamic scenarios. Our results indicate a significant reduction in the perstream allocated bandwidth when stream scheduling is used. While this reduction is obtained through statistical multiplexing, the transported streams are guaranteed stringent, deterministic quality of service (i.e., zero loss rate and small, bounded delay). In contrast to video smoothing, our approach requires virtually no buffer at the settop box since frames are delivered at their playback rate.     

Adaptive chaining scheme for distributed VOD applications

In distributed video on demand (VOD) applications, a client station buffers a shifting window of its displaying video so that the video stream can be chained from the client to another one arriving within the window, instead of consuming a server stream for each new request. This scheme is called video chaining that can reduce the load of video servers significantly. In this paper, we propose a novel adaptive chaining scheme that extends the basic chaining scheme with two new techniques: two-way bridging and multicast chaining. The two-way bridging method employs video buffers as forward and/or backward bridges to extend each video chain as long as possible. It provides nearly twice the performance gain than basic chaining in terms of server I/O load reduction. Mathematical analyses for both schemes are also given. The multicast chaining method maximizes the multicast degree of each video chain so that lower data delivery cost per video session can be achieved. Our scheme maintains the video chains optimally to shift the load to active clients so that the I/O bottleneck of video servers is released     

Group replica caching scheme for optical grid networks

This paper proposes a cache replacement scheme named group replica caching for optical grid networks. In optical grid networks, data files for job execution are replicated at multiple servers in order to distribute loads. Clients download these files via lightpaths and store them as necessary. File downloading is blocked when the corresponding lightpath cannot be established. The blocking probability of file downloading depends on location of files. The case where a file is stored in a client is ideal because blocking of lightpath establishments does not occur. However, the storage size of the client is limited. In order to efficiently use storage resources of clients, our proposed scheme focuses on the fact that clients can download files stored in surrounding servers with low blocking probability. The proposed scheme regards a group of storages of a client and its surrounding servers as one storage. In particular, they preferentially store different files. By doing so, the probability that a file is stored at the client or its surrounding servers increases. Through simulation experiments, we show that the proposed scheme improves the blocking probability of file downloading efficiently.     

Hybrid layered video encoding and caching for resource constrained environments

Video playback on a mobile device is a resource-intensive task. Since the battery life of a mobile device decreases with time, it is desirable to have a video representation which adapts dynamically to the available battery life during the playback process. A novel Hybrid Layered Video (HLV) encoding scheme is proposed, which comprises of content-aware, multi-layer encoding of texture and a generative sketch-based representation of the object outlines. Different combinations of the texture- and sketch-based representations are shown to result in distinct video states, each with a characteristic power consumption profile. Further, a smart content-aware caching scheme is proposed which is suitable for low-latency dissemination of HLV over the Internet. The proposed HLV representation, combined with the proposed caching scheme, is shown to be effective for video playback and dissemination on power-constrained mobile devices.     

An optimum power management scheme for wireless video service in CDMA systems

An optimum power management scheme is proposed for intra-frame refreshed image sequences of the wireless video service in code-division multiple-access (CDMA) systems. The end-to-end distortion of H.263 video data is first modeled when the error concealment schemes are employed. This distortion model takes into account the error propagation effects caused by the motion compensation. Then, based on the model, the target bit-error rates (BERs) of the image frames are optimized in such a way that the consumed power could be minimized under the constraint of maximum distortion. To satisfy the specified target BER requirement, an optimum power management scheme is proposed. Simulation results show that the proposed scheme considerably outperforms the conventional scheme in the sense of the decoded image quality. Additionally, the effects of the imperfect power control on the performance are also investigated.     

Scalable proxy caching of video under storage constraints

Proxy caching has been used to speed up Web browsing and reduce networking costs. In this paper, we study the extension of proxy caching techniques to streaming video applications. A trivial extension consists of storing complete video sequences in the cache. However, this may not be applicable in situations where the video objects are very large and proxy cache space is limited. We show that the approaches proposed in this paper (referred to as selective caching), where only a few frames are cached, can also contribute to significant improvements in the overall performance. In particular, we discuss two network environments for streaming video, namely, quality-of-service (QoS) networks and best-effort networks (Internet). For QoS networks, the video caching goal is to reduce the network bandwidth costs; for best-effort networks, the goal is to increase the robustness of continuous playback against poor network conditions (such as congestion, delay, and loss). Two different selective caching algorithms (SCQ and SCB) are proposed, one for each network scenario, to increase the relevant overall performance metric in each case, while requiring only a fraction of the video stream to be cached. The main contribution of our work is to provide algorithms that are efficient even when the buffer memory available at the client is limited. These algorithms are also scalable so that when changes in the environment occur it is possible, with low complexity, to modify the allocation of cache space to different video sequences.     

Precoding with interference suppression sequence scheme for OFDM-based cognitive radio systems

Orthogonal frequency division multiplexing(OFDM)is considered to be one of the promising schemes for cognitive radios(CR)systems,due to its flexibility in spectrum shaping.However,the traditional way of spectrum-notching failed to suppress out-of-band leakage enough,resulting in interference with licensed users(LUs).A novel spectrum shaping scheme is proposed in this article,where a precoder with interference suppression sequence(ISS)is for the first time introduced for shaping the spectrum of OFDM signals in OFDM-based CR systems.The precoder matrix together with ISS matrix is obtained by minimizing the power of out-of-band interference,which results in the sufficient interference suppression of OFDM signal to LUs.Analysis and simulation results show that the proposed scheme can significantly suppress the interference power to LUs at a little cost of precoding efficiency.Meanwhile,the peak-to-average-power-ratio(PAPR)is invariable and the bit-error-rate(BER)performance over Rayleigh fading channel is improved.     

On expiration-based hierarchical caching systems

Caching is an important means to scale up the growth of the Internet. Weak consistency is a major approach used in Web caching and has been deployed in various forms. The paper investigates some fundamental properties and performance issues associated with an expiration-based caching system. We focus on a hierarchical caching system based on the time-to-live expiration mechanism and present a basic model for such system. By analyzing the intrinsic timing behavior of the basic model, we derive important performance metrics from the perspectives of the caching system and end users, respectively. Based on the results for the basic model, we introduce threshold-based and randomization-based techniques to enhance and generalize the basic model further. Our results offer some important insights into a hierarchical caching system based on the weak consistency paradigm.     

IP/TV VOD网络视讯系统解决方案

分析了IP／TV VoD网络视讯系统的技术(系统结构、工作原理等)、产品特点、功能特点，给出了设计方案及其设备配置选型，结合实际的工程建设对网络进行了运行分析。     

Blockchain-based collaborative edge caching scheme fortrustworthy content sharing

Moving data from cloud to the edge network can effectively reduce traffic burden on the core network, and edge collaboration can further improve the edge caching capacity and the quality of service ( QoS). However, it is difficult for various edge caching devices to cooperate due to the lack of trust and the existence of malicious nodes. In this paper,blockchain which has the distributed and immutable characteristics is utilized to build a trustworthy collaborative edge caching scheme to make full use of the storage resources of various edge devices. The collaboration process is described in this paper, and a proof of credit (PoC) protocol is proposed, in which credit and tokens are used to encourage nodes to cache and transmit more content in honest behavior. Untrusted nodes will pay for their malicious actions such as tampering or deleting cached data. Since each node chooses strategy independently to maximize its benefits in an environment of mutual influence, a non-cooperative game model is designed to study the caching behavior among edge nodes. The existence of Nash equilibrium (NE) is proved in this game, so the edge server (ES) can choose the optimal caching strategy for all collaborative devices, including itself, to obtain the maximum rewards. Simulation results show that the system can save mining overhead as well as organize a trusted collaborative edge caching effectively.     

基于可重构路由器上缓存的流媒体协作分发策略

提出一种新颖的基于可重构路由器上缓存的协作分发策略来加速流媒体。通过网络存储即多个边缘路由器节点对热点视频数据进行合作缓存,就近为用户提供服务,从而使得流媒体服务器的性能要求尤其是带宽需求得到巨大的降低,骨干网传输的流量也明显减少,同时用户响应延迟也得到明显的改善。此外,实现了一个原型系统来评价基于路由器上缓存的流媒体协作分发策略的性能,结果表明该方案相比于现有的方案在改善网络性能以及用户体验方面取得很大的提升。     

Tile caching for scalable VR video streaming over 5G mobile networks

Currently, VR video delivery over 5G systems is still a very complicated endeavor. One of the major challenges for VR video streaming is the expectations for low latency that current mobile networks can hardly meet. Network caching can reduce the content delivery latency efficiently. However, current caching schemes cannot obtain ideal results for VR video since it requests the viewport interactively. In this paper, we propose a tiled scalable VR video caching scheme over 5G networks. VR chunks are first encoded into multi-granularity quality layers, and are then partitioned into tiles to facilitate viewport data access. By accommodating the 5G network infrastructure, the tiles are cooperatively cached in a three-level hierarchal system to reduce delivery latency. Furthermore, a quality-adaptive request routing algorithm is designed to cater for the 5G bandwidth dynamics. Experimental results show that the proposed scheme can reduce the transmission latency over conventional constant bitrate video caching schemes.     

Dynamic hierarchical collaborative caching scheme in ultra-dense networks

Pushing popular contents to the edge of the network can meet the growing demand for data traffic, reduce latency and relieve the pressure of the backhaul. However, considering the limited storage space of the base stations, it is impossible to cache all the contents, especially in ultra-dense network ( UDN). Furthermore, the uneven distribution of mobile users results in load imbalance among small base stations (SBSs) in both time and space, which also affects the caching strategy. To overcome these shortcoming, the impact of the changing load imbalance in UDN was investigated, and then a dynamic hierarchical collaborative caching (DHCC) scheme was proposed to optimize latency and caching hit rate. The storage of the SBS is logically divided into the independent caching layer and the collaborative caching layer. The independent caching layer caches the most popular contents for local users爷interest, and the collaborative caching layer caches contents as much as possible for the benefit of content diversity in the region. Different SBSs have respective storage space layer division ratios, according to their real-time traffic load. For SBSs with heavy load, the independent caching layers are allocated with more space. Otherwise, the collaborative caching layers could store more contents with larger space. The simulation results show that, DHCC improved both transmission latency and hit rate compared with existing caching schemes.     

基于信息中心5G车联网中社会感知的流媒体缓存与转发策略

5G 通信技术的到来为车载自组网（VANET）提供高质量的视频流服务奠定了基础。然而,现有的VANET 仍然采用以主机通信而非内容分发的 IP 网络来分发视频数据,造成了网络功能与设计目标之间的不匹配,为提供高质量的视频服务带来了巨大挑战。基于上述问题,提出了一种以信息为中心的社会感知流媒体缓存和转发策略（SACF）,其时间复杂度为O(m²)。首先,通过分析用户节点的行为构建社会感知的虚拟社区;然后,提出了一种视频快速转发机制来支持用户就近获取视频内容;最后,提出了一种基于社区的缓存策略来优化视频的缓存分布。仿真实验结果表明,与最新的解决方案相比,该算法的缓存命中率提高了18%,查找时延降低了33%,平均网络开销减少了14.6%。     

QoE-based video segments caching strategy in urban publictransportation system

With the rapid development of vehicle-based applications, entertainment videos have gained popularity for passengers on public vehicles. Therefore, how to provide high quality video service for passengers in typical public transportation scenarios is an essential problem. This paper proposes a quality of experience (QoE)-based video segments caching (QoE-VSC) strategy to guarantee the smooth watching experience of passengers. Consequently, this paper considers a jointly caching scenario where the bus provides the beginning segments of a video, and the road side unit (RSU) offers the remaining for passengers. To evaluate the effectiveness, QoE hit ratio is defined to represent the probability that the bus and RSUs jointly provide passengers with desirable video segments successfully. Furthermore, since passenger volume change will lead to different video preferences, a deep reinforcement learning (DRL) network is trained to generate the segment replacing policy on the video segments cached by the bus server. And the training target of DRL is to maximize the QoE hit ratio, thus enabling more passengers to get the required video. The simulation results prove that the proposed method has a better performance than baseline methods in terms of QoE hit ratio and cache costs.     

A recursive frequency-splitting scheme for broadcasting hot videos in VOD service

One way to broadcast a popular/hot video is to let multiple users share a few channels. The stress on the scarce channels can be alleviated without sacrificing viewer waiting time. One common approach is to partition the video into fixed-length segments, which are broadcast on several channels periodically. Two representative approaches are the fast broadcasting scheme and the PAGODA scheme, which can broadcast a video using k channels by having new viewers wait no longer than /spl Theta/(D/2/sup k/) and /spl Theta/(D/5/sup k/2/) time, respectively, where D is the length of the video. In this paper, we propose a new scheme, called recursive frequency splitting (RFS), that significantly improves on existing schemes in terms of viewer waiting time. Some lower bounds on the viewers' waiting time are also developed.     

A novel caching scheme for improving Internet-based mobile ad hoc networks performance

Internet-based mobile ad hoc network (Imanet) is an emerging technique that combines a wired network (e.g. Internet) and a mobile ad hoc network (Manet) for developing a ubiquitous communication infrastructure. To fulfill users’ demand to access various kinds of information, however, an Imanet has several limitations such as limited accessibility to the wired Internet, insufficient wireless bandwidth, and longer message latency. In this paper, we address the issues involved in information search and access in Imanets. An aggregate caching mechanism and a broadcast-based Simple Search (SS) algorithm are proposed for improving the information accessibility and reducing average communication latency in Imanets. As a part of the aggregate cache, a cache admission control policy and a cache replacement policy, called Time and Distance Sensitive (TDS) replacement, are developed to reduce the cache miss ratio and improve the information accessibility. We evaluate the impact of caching, cache management, and the number of access points that are connected to the Internet, through extensive simulation. The simulation results indicate that the proposed aggregate caching mechanism can significantly improve an Imanet performance in terms of throughput and average number of hops to access data items.