A dynamic caching algorithm based on internal popularity distribution of streaming media

Most proxy caches for streaming videos do not cache the entire video but only a portion of it. This is partly due to the large size of video objects. Another reason is that the popularity of different parts of a video can be different, e.g., the prefix is generally more popular. Therefore, the development of efficient cache mechanisms requires an understanding of the internal popularity characteristics of streaming videos. This paper has two major contributions. Firstly, we analyze two 6-month long traces of RTSP video requests recorded at different streaming video servers of an entertainment video-on-demand provider, and show that the traces provide evidence that the internal popularity of the majority of the most popular videos obeys a k-transformed Zipf-like distribution. Secondly, we propose a caching algorithm which exploits this empirical internal popularity distribution. We find that this algorithm has similar performance compared with fine-grained caching but requires significantly less state information.     

Optimized scalable cache management for video streaming system

An important research issue in video streaming is how to efficiently utilize the network resources to provide clients instant access to multiple video objects. Caching strategy and transmission scheme are the two essential points inside the video streaming framework. Recent research efforts on them are not sufficient due to their inflexible support for scalable encoded video streams and heterogeneous requests from clients. In this paper, we propose an optimized caching strategy (OCS) and a scalable transmission scheme (STS) for scalable coded video streaming. By exploring the characteristics of video streaming workload and system design objectives, OCS and STS work efficiently to minimize both network bandwidth cost and user access latency. Firstly, we analyze the caching problem for the proxy-assisted video streaming system and derive a maneuverable caching scenario. Secondly, we develop an efficient transmission scheme for scalable coded videos. Thirdly, we formulate a multi-objective optimization model with closed-form expressions to obtain the optimized caching strategy. Finally, with designed algorithms, an excellent compromise between two competing objectives (minimizing the bandwidth cost and the access latency) is achieved. We start our evaluation by studying the optimized caching strategy for a single video object. Then we apply the strategy to multiple video objects and illustrate the tradeoff between the optimization objectives. Our evaluation results show that compared with other caching strategies, the proposed optimized scalable caching strategy can achieve a significant reduction in bandwidth cost with even a small proxy cache size. Meanwhile, the best performance (in terms of bandwidth cost) is obtained together with the proposed scalable batch-patching transmission scheme.

COPACC: An Architecture of Cooperative Proxy-Client Caching System for On-Demand Media Streaming

Proxy caching is a key technique to reduce transmission cost for on-demand multimedia streaming. The effectiveness of current caching schemes, however, is limited by the insufficient storage space and weak cooperation among proxies and their clients, particularly considering the high bandwidth demands from media objects. In this paper, we propose COPACC, a cooperative proxy-and-client caching system that addresses the above deficiencies. This innovative approach combines the advantages of both proxy caching and peer-to-peer client communications. It leverages the client-side caching to amplify the aggregated cache space and rely on dedicated proxies to effectively coordinate the communications. We propose a comprehensive suite of distributed protocols to facilitate the interactions among different network entities in COPACC. It also realizes a smart and cost-effective cache indexing, searching, and verifying scheme. Furthermore, we develop an efficient cache allocation algorithm for distributing video segments among the proxies and clients. The algorithm not only minimizes the aggregated transmission cost of the whole system, but also accommodates heterogeneous computation and storage constraints of proxies and clients. We have extensively evaluated the performance of COPACC under various network and end-system configurations. The results demonstrate that it achieves remarkably lower transmission cost as compared to pure proxy-based caching with limited storage space. On the other hand, it is much more robust than a pure peer-to-peer communication system in the presence of node failures. Meanwhile, its computation and control overheads are both kept in low levels     

基于后缀动态多缓存协作的流媒体分发技术

在Internet上高效传输流媒体数据是推广诸如视频点播等应用的基础．现有方案仅考虑了采用单代理结构的前缀缓存和服务器调度来降低骨干网带宽消耗和服务器负载．在带前缀缓存的Batch patching基础上提出了后缀的动态缓存算法ICBR，并提出了基于ICBR缓存算法的多缓存协作体系结构及协作算法MCC，仿真结果表明，基于ICBR的多缓存协作显著地降低了获取补丁而导致的骨干网带宽的消耗，提高了客户端QoS同时也降低了服务器负载．     

Fine-Grained Scalable Video Caching for Heterogeneous Clients

Much research has focused on caching adaptive videos to improve system performance for heterogeneous clients with diverse access bandwidths. However, existing rate-adaptive caching systems, which are based on layered coding or transcoding, often suffer from a coarse adaptation and/or a high computation overhead. In this paper, we propose an innovative rate-adaptive caching framework that enables low-cost and fine-grained adaptation by using MPEG-4 fine-grained scalable videos. The proposed framework is both network-aware and media-adaptive; i.e., the clients can be of heterogeneous streaming rates, and the backbone bandwidth consumption can be adaptively controlled. We develop efficient cache management schemes to determine the best contents to cache and the optimal streaming rate to each client under the framework. We demonstrate via simulations that, compared to nonadaptive caching, the proposed framework with the optimal cache management not only achieves a significant reduction in the data transmission cost, but also enables a flexible utility assignment for the heterogeneous clients. Our results also show that the framework maintains a low computational overhead, which implies that it is practically deployable.     

Protocol considerations for a prefix-caching proxy for multimedia streams

The increasing popularity of multimedia streaming applications introduces new challenges in content distribution. Web-initiated multimedia streams typically experience high start-up delay, due to large protocol overheads and the poor delay, throughput, and loss properties of the Internet. Internet service providers can improve performance by caching the initial segment (the prefix) of popular streams at proxies near the requesting clients. The proxy can initiate transmission to the client while simultaneously requesting the remainder of the stream from the server. This paper analyzes the challenges of realizing a prefix-caching service in the context of the IETF's Real-Time Streaming Protocol (RTSP), a multimedia streaming protocol that derives from HTTP. We describe how to exploit existing RTSP features, such as the Range header, and how to avoid several round-trip delays by caching protocol information at the proxy. Based on our experiences, we propose extensions to RTSP that would ease the development of new multimedia proxy services. In addition, we discuss how caching the partial contents of multimedia streams introduces new challenges in cache coherency and feedback control. Then, we briefly present our preliminary implementation of prefix caching on a Linux-based PC, and describe how the proxy interoperates with the RealNetworks server and client.     

WSN中改进的IPv6路由查找算法

针对无线传感器网络(WSN)中的全局单播地址,提出一种IPv6快速路由查找机制。利用布鲁姆过滤器作为存储结构,以合适的存储方法降低错误率,采用最长前缀匹配算法合理分配前缀,以减少静态随机存取存储器的数量,降低成本。实验结果表明,利用该算法可以减少每一次查找的散列探头,从而提高路由表的查找速度,改善WSN的性能。     

IP路由缓存技术研究

针对目前用于IP路由查找的地址缓存技术和前缀缓存技术的局限性,分析了骨干网路由表前缀重叠特征,提出了一种基于阈值的IP路由缓存方法,该方法结合了地址缓存和前缀缓存技术,无需进行前缀扩展,克服了地址缓存技术缓存空间要求过大、前缀缓存技术无法缓存内部前缀节点的问题,在缓存空间、缓存命中率、缓存公平性以及路由增量更新方面具有优势;仿真实验表明对于路由条目超过260000的路由表,缓存空间大小为30000,选择阈值K=4时97%以上的节点可实现1:1缓存,其余节点采用地址缓存,缓存失效率小于0.02,可以用小的缓存空间实现高速线速转发.     

基于协作小小区与流行度预测的在线热点视频缓存更新策略

针对无线移动设备数量的指数增长使得异构协作小小区（SBS）将承载大规模的流量负载问题，提出了一种基于协作SBS与流行度预测的在线热点视频缓存更新方案（OVCRP）。首先，分析在线热点视频的流行度在短期内变化情况；然后，构建k近邻模型进行在线热点视频流行度的预测；最后，确定在线热点视频的缓存更新位置。为了选择合适的位置存放在线热点视频，以最小化总体传输时延为目标，建立数学模型，设计整数规划优化算法。仿真实验结果显示，与随机缓存（RANDOM）、最近最少使用（LRU）、最不经常使用（LFU）方案相比，OVCRP在平均缓存命中率和平均访问时延方面具有明显的优势，因此减轻了协作SBS的网络负担。     

大规模分布式VoD中可扩展的影片缓存配置策略

提出了在VoD系统中减少综合性资源开销的一种灵活的分布式层次化影片缓存(Cache)配置策略。在采用单播传输情况下分析了标志着系统集成、服务器的流支持、存储及网络连接等的综合性资源开销。性能分析结果表明：用该策略构成的系统比传统的方案具有更小的开销，并且可以用较低的代价获得更多影片的服务。     

Tabu search algorithm for routing,modulation and spectrum allocation in elastic optical network with anycast and unicast traffic

The paper presents a novel method based on the standard tabu search (TS) approach, dedicated to solve the routing, modulation and spectrum allocation (RMSA) problem in elastic optical networks (EONs). The considered formulation of the RMSA problem covers simultaneously unicast (one-to-one) and anycast (one-to-one-of-many) traffic demands. This is a very important issue taking into account the fact that anycasting gains more and more importance in contemporary Internet due the growing popularity of services like cloud computing, content delivery networks, and video streaming. In this paper, we formulate RMSA as an integer linear programming (ILP) problem and we study four different objective functions, which are related to, respectively, cost, power consumption, maximum and average spectrum usage. We evaluate the performance of our TS method based on the comparison with both optimal results yielded by the CPLEX solver and the results obtained by reference heuristic algorithms proposed in the literature. Moreover, we evaluate benefits of the use of anycasting in EONs. The performed simulation experiments demonstrate that the proposed algorithm outperforms other reference methods. What is more, we show that the anycast transmission can provide significant savings compared to the typical unicast transmission.     

具有聚合性质的无证书代理重签名方案

现有的代理重签名大多是基于证书或身份的密码系统,存在证书管理和密钥托管等问题。为了克服已有代理重签名方案的安全性依赖强和计算开销大等缺陷,结合代理重签名和无证书公钥密码体制,设计了一种具有聚合性质的无证书代理重签名方案,可将任意长度集合上的签名或者重签名聚合成一个集合上的签名,有效减少了签名验证的计算代价和通信成本。分析结果表明,新方案具有较短的签名长度和重签名长度,并且在k MCDH假设下是存在性不可伪造的。     

A proxy-based integrated cache consistency and mobility management scheme for client–server applications in Mobile IP systems

In this paper, we investigate a proxy-based integrated cache consistency and mobility management scheme for supporting client–server applications in Mobile IP systems with the objective to minimize the overall network traffic generated. Our cache consistency management scheme is based on a stateful strategy by which cache invalidation messages are asynchronously sent by the server to a mobile host (MH) whenever data objects cached at the MH have been updated. We use a per-user proxy to buffer invalidation messages to allow the MH to disconnect arbitrarily and to reduce the number of uplink requests when the MH is reconnected. Moreover, the user proxy takes the responsibility of mobility management to further reduce the network traffic. We investigate a design by which the MH’s proxy serves as a gateway foreign agent (GFA) as in the MIP Regional Registration protocol to keep track of the address of the MH in a region, with the proxy migrating with the MH when the MH crosses a regional area. We identify the optimal regional area size under which the overall network traffic cost, due to cache consistency management, mobility management, and query requests/replies, is minimized. The integrated cache consistency and mobility management scheme is demonstrated to outperform MIPv6, no-proxy and/or no-cache schemes, as well as a decoupled scheme that optimally but separately manages mobility and service activities in Mobile IPv6 environments.     

一种移动流媒体分层协同缓存系统

随着移动互联网的发展和用户数量的增加,网络中的音视频服务普遍采用动态缓存机制来减轻回程主干网的带宽压力和提高用户的观影体验。如何根据网络和用户需求,调整不同节点的缓存内容,以减少主干网的带宽压力,是当前缓存部署迫切需要解决的问题。基于子模函数理论,本文提出主动和被动资源分配调整方案及其算法。主动方案根据资源的流行度把视频文件部署到缓存节点上,以达到用户访问代价的最小化;被动方案根据音视频流行度的变化对节点上缓存的内容进行实时调整,以提高缓存资源的利用率和用户体验,降低主干网的带宽消耗。最小访问代价算法的复杂度与缓存空间容量大小相关,在缓存空间紧张时能快速迭代出资源的分配方案。数值仿真表明,主动和被动分配资源分配方案能有效降低远程服务器的带宽压力和提高用户体验。     

移动互联网视频传输优化的架构研究

随着3G移动互联网的快速发展,在手机等移动终端上看视频成为一种日常应用.但互联网上的大部分视频对于移动用户而言,其码率相对较大,而且移动用户的可用带宽受环境影响变化大,不稳定,影响了用户观看视频的体验.提出一种针对移动互联网的视频传输优化解决方案的系统架构,该架构从缓存和压缩两个方面入手,通过缓存缓解运营商的骨干网流量压力,通过视频压缩降低视频码率以满足用户的实际接入带宽.该架构既为运营商节约了带宽、降低了运营成本,同时也保证用户观看视频的连续性,提高用户体验.     

一种新的基于分区的多媒体代理协作管理策略

多媒体代理缓存是提高媒体流化质量和减轻网络负载的重要手段，将基于协作的多媒体代理缓存技术引入无线网络，提出一种新的分区缓存管理模型（Partition-based caching manager,PBCM)，通过对系统中各个代理的部分缓存空间（称为静态分区）采取集中式管理，可以合理配置缓存资源，降低缓存的冗余度，从全局角度优化系统的整体性能，具体地，PBCM中制定了一种全局对象放置策略来管理静态分区缓存的内容，该策略被模型化为一个优化问题，并采用改进遗传算法来求解，仿真实验表明该模型及算法是有效可行的。     

MSC: a multi-version shared caching for multi-bitrate VoD services

Recently, many Video-on-Demand (VoD) service providers try to attract as many users as possible by offering multi-bitrate video streaming services with differentiated qualities. Many researches focus on video layered coding (e.g., scalable video coding, SVC). However, SVC is not widely used in VoD industry. Another solution, multi-version videos, can be classified into online transcoding and pre-stored multi-version videos. Online transcoding is a CPU-intensive and costly task, so it is not suitable for large-scale VoD applications. In this paper, we study how to improve caching efficiency based on pre-stored multi-version videos. We leverage the sharing probability among different versions of the same video and propose a multi-version shared caching (MSC) method to maximize the benefit of caching proxy. If the desired version is not in the cache while the higher neighbor version is in, MSC transmits the higher version streaming to user temporarily. In this case, MSC can make full use of the caching resources to improve the cache hit ratio and decrease users’ average waiting time. Simulation results show that MSC outperforms the others in the cache hit ratio and the average waiting time.     

Caching collaboration and cache allocation in peer-to-peer video systems

Providing scalable video services in a peer-to-peer (P2P) environment is challenging. Since videos are typically large and require high communication bandwidth for delivery, many peers may be unwilling to cache them in whole to serve others. In this paper, we address two fundamental research problems in providing scalable P2P video services: (1) how a host can find enough video pieces, which may scatter among the whole system, to assemble a complete video; and (2) given a limited buffer size, what part of a video a host should cache and what existing data should be expunged to make necessary space. We address these problems with two new ideas: Cell caching collaboration and Controlled Inverse Proportional (CIP) cache allocation. The Cell concept allows cost-effective caching collaboration in a fully distributed environment and can dramatically reduce video lookup cost. On the other hand, CIP cache allocation challenges the conventional caching wisdom by caching unpopular videos in higher priority. Our approach allows the system to retain many copies of popular videos to avoid creating hot spots and at the same time, prevent unpopular videos from being quickly evicted from the system. We have implemented a Gnutella-like simulation network and use it as a testbed to evaluate the proposed technique. Our extensive study shows convincingly the performance advantage of the new scheme.

A window-assisted video partitioning strategy for partitioning and caching video streams in distributed multimedia systems

In this paper, we address the issue of efficiently streaming a set of heterogenous videos under the constraint of service latency over a scalable multimedia systems. We propose a novel strategy, referred to as window-assisted video partitioning (WAVP), for rendering cost-effective multimedia services. The objective is to minimize the service cost and maximize the number of requests that can be successfully served under resources constraints (cache capacity and link bandwidth). We formulate the problem of video partitioning as an optimization of both bandwidth resources and cache space, and derive the optimal schedule window for different video portions under consideration of time constraints, the popularities and the sizes of the video portions. In WAVP, video are partitioned into multiple portions and delivered according to by adaptive schedule windows. We prove that WAVP strategy not only optimize the service cost but also be able to serve requests under the time constraints without causing too much delay. We conduct mathematical analysis and derive certain performance bounds that quantify the overall performance of the strategy. It shows that the service cost can be optimized by adjusting the schedule window and resources utilization can be improved as video streams are partitioned into multiple portions. We evaluate the performance under several influencing parameters such as available bandwidth, cache capacity, and partition gradients. Simulation results show that our proposed method can not only significantly reduce the service cost under tight time constraints and with low partition overhead, but also balance the utilization of network resources to achieve high acceptance ratio with low average service cost.     

Form-based proxy caching for database-backed web sites: keywords and functions

Web caching proxy servers are essential for improving web performance and scalability, and recent research has focused on making proxy caching work for database-backed web sites. In this paper, we explore a new proxy caching framework that exploits the query semantics of HTML forms. We identify two common classes of form-based queries from real-world database-backed web sites, namely, keyword-based queries and function-embedded queries. Using typical examples of these queries, we study two representative caching schemes within our framework: (i) traditional passive query caching, and (ii) active query caching, in which the proxy cache can service a request by evaluating a query over the contents of the cache. Results from our experimental implementation show that our form-based proxy is a general and flexible approach that efficiently enables active caching schemes for database-backed web sites. Furthermore, handling query containment at the proxy yields significant performance advantages over passive query caching, but extending the power of the active cache to do full semantic caching appears to be less generally effective.