Proxy-assisted scalable periodic broadcasting of videos for heterogeneous clients

Periodic broadcasting (PB) is a scalable technique for providing video-on-demand services. It significantly reduces server input and output (I/O) and backbone network bandwidth requirements, but increases the clients’ need for storage space and network bandwidth. Traditional protocols assume homogeneous clients with identical resources. In practice, however, clients have very different bandwidths, which are usually not sufficient for video-on-demand service from a PB server. Existing work on heterogeneous clients has focused on devising broadcast schedules that cater to low-bandwidth clients; these schedules inevitably require additional backbone network bandwidth between the server and the clients. In this paper, we propose a scheme to significantly reduce the waiting time of all heterogeneous clients, without the need for any additional backbone bandwidth. This scheme uses a proxy buffer within video-on-demand systems using PB. In the proposed system, the server broadcasts a video using one of the traditional PB protocols. Simultaneously, the proxy receives the stream from the server and stores it in its local buffer, then broadcasts the stored data to the clients in its local network. Because the proxy provides extra, transparent channels to the server, clients are likely to reduce their reception bandwidth requirements through the use of efficient reception schedules using the extra channels.     

Presentation planning for distributed VoD systems

A distributed video-on-demand (VoD) system is one where a collection of video data is located at dispersed sites across a computer network. In a single site environment, a local video server retrieves video data from its local storage device. However, in distributed VoD systems, when a customer requests a movie from the local server, the server may need to interact with other servers located across the network. In this paper, we present different types of presentation plans that a local server can construct in order to satisfy a customer request. Informally speaking, a presentation plan is a temporally synchronized sequence of steps that the local server must perform in order to present the requested movie to the customer. This involves obtaining commitments from other video servers, obtaining commitments from the network service provider, as well as making commitments of local resources, while keeping within the limitations of available bandwidth, available buffer, and customer data consumption rates. Furthermore, in order to evaluate the quality of a presentation plan, we introduce two measures of optimality for presentation plans: minimizing wait time for a customer and minimizing access bandwidth which, informally speaking, specifies how much network/disk bandwidth is used. We develop algorithms to compute three different optimal presentation plans that work at a block level, or at a segment level, or with a hybrid mix of the two, and compare their performance through simulation experiments. We have also mathematically proven effects of increased buffer or bandwidth and data replications for presentation plans which had previously been verified experimentally in the literature.     

Loopback: exploiting collaborative caches for large-scale streaming

In this paper, we propose a Loopback approach in a two-level streaming architecture to exploit collaborative client/proxy buffers for improving the quality and efficiency of large-scale streaming applications. At the upper level we use a content delivery network (CDN) to deliver video from a central server to proxy servers. At the lower level a proxy server delivers video with the help of collaborative client caches. In particular, a proxy server and its clients in a local domain cache different portions of a video and form delivery loops. In each loop, a single video stream originates at the proxy, passes through a number of clients, and finally is passed back to the proxy. As a result, with limited bandwidth and storage space contributed by collaborative clients, we are able to significantly reduce the required network bandwidth, I/O bandwidth, and cache space of a proxy. Furthermore, we develop a local repair scheme to address the client failure issue for enhancing service quality and eliminating most required repairing load at the central server. For popular videos, our local repair scheme is able to handle most of single-client failures without service disruption and retransmissions from the central server. Our analysis and simulations have shown the effectiveness of the proposed scheme.     

Reducing bandwidth requirement for delivering video over wide area networks with proxy server

Due to the high bandwidth requirement and rate variability of compressed video, delivering video across wide area networks (WANs) is a challenging issue. Proxy servers have been used to reduce network congestion and improve client access time on the Internet by caching passing data. We investigate ways to store or stage partial video in proxy servers to reduce the network bandwidth requirement over WAN. A client needs to access a portion of the video from a proxy server over a local area network (LAN) and the rest from a central server across a WAN. Therefore, client buffer requirement and video synchronization are to be considered. We study the tradeoffs between client buffer, storage requirement on the proxy server, and bandwidth requirement over WAN. Given a video delivery rate for the WAN, we propose several frame staging selection algorithms to determine the video frames to be stored in the proxy server. A scheme called chunk algorithm, which partitions a video into different segments (chunks of frames) with alternating chunks stored in the proxy server, is shown to offer the best tradeoff. We also investigate an efficient way to utilize client buffer when the combination of video streams from WAN and LAN is considered.     

基于CDN和P2P技术的混合流媒体内容分发机制研究

采用核心层通过P2P技术对混合流媒体内容分发网络进行优化,即根据区域将边缘代理服务器间以P2P的方式进行协作式内容存储,终端用户以P2P方式进行分发,从而达到更好地利用边缘服务器的缓存空间,增大骨干网的带宽利用率,提升分发能力的目的.     

Delivery of compressed videos from video servers employing cycle-based data-block retrieval discipline

The significant frame size variability exhibited in the compressed videos imposes a great challenge on network delivery. In this paper we propose an efficient flow control scheme, employed in the peer stations (i.e., servers and clients), for delivery of prestored compressed videos in a video-on-demand (VOD) system. This scheme resorts to an off-line analysis on the video frame sizes and server properties for figuring out the necessary buffer space and network bandwidth. The server platform of particular interest obeys a cycle-based data-block retrieval discipline, which is an essential technique to reduce the disk seek time for leveraging the disk throughput for supporting a large number of concurrent video accesses. Such a discipline is taken into account here to guarantee smooth delivery of variable-bit-rate videos. In run-time a server-driven control model is in use, where a server performs the primary flow control task, without relying on any feedback from clients. The scheme has been implemented in our prototype VOD system to support both unicast- and multicast communication paradigms under an RSVP-enabled network.     

Design a progressive video caching policy for video proxy servers

Proxy servers have been used to cache web objects to alleviate the load of the web servers and to reduce network congestion on the Internet. In this paper, a central video server is connected to a proxy server via wide area networks (WANs) and the proxy server can reach many clients via local area networks (LANs). We assume a video can be either entirely or partially cached in the proxy to reduce WAN bandwidth consumption. Since the storage space and the sustained disk I/O bandwidth are limited resources in the proxy, how to efficiently utilize these resources to maximize the WAN bandwidth reduction is an important issue. We design a progressive video caching policy in which each video can be cached at several levels corresponding to cached data sizes and required WAN bandwidths. For a video, the proxy server determines to cache a smaller amount of data at a lower level or to gradually accumulate more data to reach a higher level. The proposed progressive caching policy allows the proxy to adjust caching amount for each video based on its resource condition and the user access pattern. We investigate the scenarios in which the access pattern is priorly known or unknown and the effectiveness of the caching policy is evaluated.     

Throughput optimization for video streaming proxy servers based on video staging

A video streaming proxy server needs to handle hundreds of simultaneous connections between media servers and clients. Inside, every video arrived at the server and delivered from it follows a specific arrival and delivery schedule. While arrival schedules compete for incoming network bandwidth, delivery schedules compete for outgoing network bandwidth. As a result, a proxy server has to provide sufficient buffer and disk cache for storage, together with memory space, disk space and disk bandwidth. In order to optimize the throughput, a proxy server has to govern the usage of these resources. In this paper, we first analyze the property of a traditional smoothing algorithm and a video staging algorithm. Then we develop, based on the smoothing algorithm, a video staging algorithm for video streaming proxy servers. This algorithm allows us to devise an arrival schedule based on the delivery schedule. Under this arrival and delivery schedule pair, we can achieve a better resource utilization rate gracefully between different parameter sets. It is also interesting to note that the usage of the resources such as network bandwidth, disk bandwidth and memory space becomes interchangeable. It provides the basis for inter-resource scheduling to further improve the throughput of a video streaming proxy server system.

Assessing the efficiency of stream reuse techniques in P2P video-on-demand systems

Many works have reported simulated performance benefits of stream reuse techniques such as batching, chaining, and patching to the scalability of VoD systems. However, the relative contribution of such techniques has been rarely evaluated in practical implementations of scalable VoD servers. In this work, we investigated the efficiency of representative stream reuse techniques on the GloVE system, a low-cost scalable VoD platform whose resulting performance depends on the combination of the stream techniques it uses. More specifically, we evaluated performance of the GloVE system on delivering multiple MPEG-1 videos to clients connected to the server through a 100 Mbps Ethernet switch, and arrival rates varying from 6 to 120 clients/min. We present experimental results including startup latency, occupancy of server's channels, and aggregate bandwidth that GloVE demanded for several combinations of stream reuse techniques. Overall, our results reveal that stream reuse techniques in isolation offer limited performance scalability to VoD systems and only balanced combination of batching, chaining, and patching explains the scalable performance of GloVE on delivering highly popular videos with low startup latency while using the smallest number of server's channels.     

PopCap: popularity oriented proxy caching for peer-assisted Internet video-on-demand streaming services

With the success of Internet video-on-demand (VoD) streaming services, the bandwidth required and the financial cost incurred by the host of the video server becoming extremely large. Peer-to-peer (P2P) networks and proxies are two common ways for reducing the server workload. In this paper, we consider a peer-assisted Internet VoD system with proxies deployed at domain gateways. We formally present the video caching problem with the objectives of reducing the video server workload and avoiding inter-domain traffic, and we obtain its optimal solution. Inspired by theoretical analysis, we develop a practical protocol named PopCap for Internet VoD services. Compared with previous work, PopCap does not require additional infrastructure support, is inexpensive, and able to cope well with the characteristic workloads of Internet VoD services. From simulation-based experiments driven by real-world data sets from YouTube, we find that PopCap can effectively reduce the video server workload, therefore provides a superior performance regarding the video server’s traffic reduction.     

视频服务器网络中影像对象映射问题的研究

视频服务器网络中的影像对象映射问题是一种新的组合优化问题.服务器网络可以建立在基于局域网的工作站网络之上,也可以建立在广域网之上.基于对用户的服务请求模式、服务器网络的存储容量和通信带宽等因素的综合考虑,研究了服务器网络中影像对象映射问题,利用局部搜索算法给出了一套对该映射问题的解决方案.然后用一套基准集实例对给出的算法集进行验证.结果表明,在较短的计算时间内,该算法可以得到近似最优解的方案.     

信息服务网中Internet代理服务器的设计

讨论在ＶｏＤ系统中Ｉｎｔｅｒｎｅｔ代理服务器方案与设计,提出在ＶｏＤ中采用Ｉｎｔｅｒｎｅｔ网络层代理服务方式,网络层代理具有支持Ｉｎｔｅｒｎｅｔ未知与来出现服务的优点,并且对用户透明,安全性高,给出了ＩＰ变换源端口代理的原理,采用了环形列表法来实现正,反代理变换。     

Efficient support for interactive service in multi-resolution VOD systems

Advances in high-speed networks and multimedia technologies have made it feasible to provide video-on-demand (VOD) services to users. However, it is still a challenging task to design a cost-effective VOD system that can support a large number of clients (who may have different quality of service (QoS) requirements) and, at the same time, provide different types of VCR functionalities. Although it has been recognized that VCR operations are important functionalities in providing VOD service, techniques proposed in the past for providing VCR operations may require additional system resources, such as extra disk I/O, additional buffer space, as well as network bandwidth. In this paper, we consider the design of a VOD storage server that has the following features: (1) provision of different levels of display resolutions to users who have different QoS requirements, (2) provision of different types of VCR functionalities, such as fast forward and rewind, without imposing additional demand on the system buffer space, I/O bandwidth, and network bandwidth, and (3) guarantees of the load-balancing property across all disks during normal and VCR display periods. The above-mentioned features are especially important because they simplify the design of the buffer space, I/O, and network resource allocation policies of the VOD storage system. The load-balancing property also ensures that no single disk will be the bottleneck of the system. In this paper, we propose data block placement, admission control, and I/O-scheduling algorithms, as well as determine the corresponding buffer space requirements of the proposed VOD storage system. We show that the proposed VOD system can provide VCR and multi-resolution services to the viewing clients and at the same time maintain the load-balancing property. Received June 9, 1998 / Accepted April 26, 1999     

PopCap: popularity oriented proxy caching for peer-assisted Internet video-on-demand streaming services

With the success of Internet video-on-demand (VoD) streaming services, the bandwidth required and the financial cost incurred by the host of the video server becoming extremely large. Peer-to-peer (P2P) networks and proxies are two common ways for reducing the server workload. In this paper, we consider a peer-assisted Internet VoD system with proxies deployed at domain gateways. We formally present the video caching problem with the objectives of reducing the video server workload and avoiding inter-domain traffic, and we obtain its optimal solution. Inspired by theoretical analysis, we develop a practical protocol named PopCap for Internet VoD services. Compared with previous work, PopCap does not require additional infrastructure support, is inexpensive, and able to cope well with the characteristic workloads of Internet VoD services. From simulation-based experiments driven by real-world data sets from YouTube, we find that PopCap can effectively reduce the video server workload, therefore provides a superior performance regarding the video server’s traffic reduction.     

Staggered push - a linearly scalable architecture for push-based parallel video servers

With the rapid performance improvements in low-cost PCs, it becomes increasingly practical and cost-effective to implement large-scale video-on-demand (VoD) systems around parallel PC servers. This paper proposes a novel parallel video server architecture where video data are striped across an array of autonomous servers connected by an interconnection network. To coordinate data transmissions from multiple autonomous servers to a client station, a staggered push scheduling algorithm is proposed. A system model is constructed to quantify the performance of the architecture. Unlike most studies, this work does not assume the existence of a global clock among the servers and tackles two problems arising from server asynchrony: inconsistent schedule assignment and traffic overlapping. The former problem is solved by using an admission scheduler and the latter problem is solved by an over-rate transmission scheme. Analytical results prove a remarkable property of the staggered push architecture: as long as the network has sufficient capacity, the system can be scaled up linearly to an arbitrary number of servers. Design examples and numerical results are used to evaluate the proposed architecture under realistic assumptions and to compare it against other architecture.     

Efficient Movie Retrieval Strategies for Movie-on-Demand Multimedia Services on Distributed Networks

In this paper, for a network-based multimedia Video/Movie-on-demand(VoD/MoD) service, we design and analyze efficient retrieval strategies to minimize both the access times of the movies and the block rates. We consider a heterogeneous set of servers and a generic network topology in which clients can request for movies from any site. We design and analyze a multiple servers retrieval strategy (MSRS) to retrieve the movies requested by the clients and present a rigorous analysis on its performance with respect to access times of the requested movies and the block rates. A generalized approach of MSRS is designed in a judicious manner using a two-step approach. In the first step, we partition the available bandwidth among the requested movies and in the second step, we derive optimal portions of the movies to be retrieved from each of the servers for each movie, based on allocated bandwidths in the first step. Thus, with the optimal playback portions of the movies using aggregate retrieval bandwidth from several servers, the access times of the movies are minimized. In the first step, in addition to the access times, we minimize the block rates by balancing the total accesses/requests among the servers. In generating the retrieval schedule, our scheme utilizes the available bandwidth (resource) among the servers and guarantees to use less buffer space than a single server retrieval strategy (SSRS). With this two-step approach, a complete flexibility is provided in tuning the access times of the movies and also shown to be robust to any variations in the user access rates of the movies, in reality. Rigorous simulation experiments are presented to observe the performance of MSRS with respect to some important system dependent parameters. Comparing with SSRS, MSRS shows better performance in the simulation.     

Modeling and analysis of multi-channel P2P VoD systems

Peer-to-Peer (P2P) technology has recently become a tremendously attractive solution to offload servers in large-scale Video-on-Demand (VoD) applications by utilizing the upload capability of participating peers. However, the alleviation of server load may not be very effective in the multi-channel P2P VoD systems due to the intra-channel and inter-channel upload bandwidth imbalances. In this paper, we evaluate the impact of these bandwidth imbalances on the system performance through two analytically models: a queuing network model which describes the whole system, and a stage-based model which describes a single channel. Our models capture several aspects of peer behavior, such as participating in the system, sojourning in a channel, downloading and uploading the content, wandering around channels and leaving the system. We apply our models to three potential P2P VoD designs: Naive bandwidth Allocation Design (NAD), Independent-channel Chunk-aware bandwidth Allocation design (ICA) and Cross-channel Chunk-aware bandwidth Allocation design (CCA). By developing an asymptotic theory to provide theoretical results, we analytically show that ICA can perform better than NAD, and CCA can perform best of the three designs in terms of server load. We also present optimization problems and simple heuristic strategies for ICA and CCA. Our analytical results are validated by extensive simulations.     

Frame Selection for Dynamic Caching Adjustment in Video Proxy Servers

By caching video data, a video proxy server close to the clients can be used to assist video delivery and alleviate the load of video servers. We assume a video can be partially cached and a certain number of video frames are stored in the proxy server. In our setting, the proxy server is allowed to cache the passing data from the video server. A video provides several options (levels) in terms of bandwidth requirement over the server-proxy path. For each video, the proxy server decides to cache a smaller amount of data at a lower level or to accumulate more data to reach a higher level. The proxy server can dynamically adjust the cached video data by choosing an appropriate level based on the network condition or the popularity of the video. We propose a frame selection scheme, Dynamic Chunk Algorithm, to determine which frames are to be cached in the proxy server for the dynamic caching adjustment scenario. The algorithm guarantees the rate constraint over the server-proxy path to be satisfied for each level. This approach also maintains the set of cached frames at a higher level as a superset of the cached frames at a lower level. Hence, it enforces the proxy server to simply cache more data without dropping frames when it intends to reduce network bandwidth consumption for a video and vice versa.     

流内容分送中的媒体后缀动态缓存技术研究

基于带前缀缓存的流调度方案OBP（optimized batch patching）提出了媒体后缀的增量缓存算法IC-BP和预分配缓存算法PA-BP,推导出两种算法下传输单一流媒体对象各自所需的平均骨干带宽、服务器平均使用输出通道数和代理所需最大缓存容量,并分析了以上两种缓存算法的综合传输代价．结果表明,两种缓存算法均有效降低了骨干带宽消耗和服务器负载,传输代价均明显低于带前缀缓存的OBP．而PA-BP克服了IC-BP算法中每次批处理调度时都至少需请求一个批处理长度补丁的缺点．因而具有更低的传输代价,其性能优于IC-BP缓存算法．