The Analysis and Performance of Multi-Rate Service in Distributed Video-on-Demand Systems

In this paper, we develop an end-to-end analysis of a distributed Video-on-Demand (VoD) system that includes an integrated model of the server and the network subsystems with analysis of its impact on client operations. The VoD system provides service to a heterogeneous client base at multiple playback rates. A class-based service model is developed where an incoming video request can specify a playback rate at which the data is consumed on the client. Using an analytical model, admission control conditions at the server and the network are derived for multi-rate service. We also develop client buffer requirements in presence of network delay bounds and delay jitter bounds using the same integrated framework of server and network subsystems. Results from an extensive simulation show that request handling policies based on limited redirection of blocked requests to other resources perform better than load sharing policies. The results also show that downgrading the service for blocked requests to a lower bitrate improves VoD system performance considerably. Combining the downgrade option with restrictions on access to high bitrate request classes is a powerful tool for manipulating an incoming request mix into a workload that the VoD system can handle.     

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.     

DVB-IPTV content download services—overview and use cases

IPTV services have been widely deployed by network operators around the world over the last years. However, real-time streaming of Linear TV and Video-on-Demand (VoD) offerings, especially in High Definition quality, still puts a high burden on the network and content servers concerning bandwidth, Quality-of-Service, processing performance and scalability if 100.000s of users have to be supported simultaneously. While multicast delivery can cope with some of these problems for Linear TV services, the unicast VoD services cannot take advantage of that and especially the request for on-demand content is expected to substantially grow in the future. With the introduction of Content Download Services (CDSs), operators have the option to provide IPTV services in innovative ways: They can provide high-quality video services to users with limited access bandwidth, offload the streaming request for blockbuster movies at peak times from the VoD servers or provided personalized advertisements for insertion into a live program event in advance to the users end device. The Digital Video Broadcast (DVB) Project has recently finalized its CDS specification within its IPTV specification efforts. DVB CDS supports push and pull delivery models with unicast, multicast and peer-to-peer distribution in order to enable various business models and use cases. In this work we introduce the specified technology and map it to example use cases and business models.     

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.     

Designing and scaling distributed VoD servers

Planning Video-on-Demand (VoD) services based on the server architecture and the available equipment is always a challenging task. We created a formal model to support the design of distributed video servers that adapt dynamically and automatically to the changing client demands, network and host parameters. The model makes giving estimations about the available throughput possible, and defines evaluation criteria for VoD services relating to utilization and load balance, video usage, client satisfaction and costs. The dynamism of the frame model originates from the possible state transitions which have to be defined in a core model. The core model is responsible for configuration recommendation which determines how clients are served depending on the properties of their requests, system configuration and system load. Furthermore, it decides on the optimal placement of the server components in the network. The usability of the model is illustrated on examples.     

VoD on steroids : Optimized content delivery using distributed video servers over best-effort Internet

This paper addresses the problem of delivering a long-duration continuous media document, typically a movie, over unreliable communication links like the ones that make up the Internet. Packet loss/drop is one of the main problems that plague Internet's use for offering multimedia services. The framework presented here addresses analytically this problem by offering closed-form solutions for partitioning and scheduling the delivery of a document by multiple spatially distributed servers. The goal is to offer uninterrupted playback to clients while minimizing their access-time.The solid mathematical foundation presented, enables the study of multi-server document delivery using unreliable communications for both CBR and VBR media. It is also shown how slow connections that would otherwise prevent the deployment of Movie-on-Demand class services, could be used to offer such services in an optimal manner. The paper also addresses the problem of optimally arranging the available servers.A rigorous simulation study that explores the potential of the proposed approach concludes the paper. Our simulations show a super-linear speedup in access-times and also the robustness of the proposed scheme, capable of handling unknown network conditions by shifting server “load”.     

Access Time Minimization for Distributed Multimedia Applications

The problem of minimizing the access time of a requested multimedia (MM) document on a network based environment is addressed. A generalized version of this problem is formulated and retrieval strategies that minimize the access time of the user-requested MM document from a pool of MM servers are proposed. To this end, we design single-installment and multi-installment MM document retrieval strategies, through which the minimization of access time can be carried out. The main idea is to utilize more than one MM server in downloading the requested document. Each server assumes the responsibility of uploading a predetermined portion of the entire document in a particular order. Single- and multi-installment strategies differ in the number of disjoint document pieces each server sends to the client. We first introduce a directed flow graph (DFG) model to represent the retrieval process and generate a set of recursive equations using this DFG. Then, we derive closed-form solutions for the portions of the MM document downloaded from the various servers and the corresponding access time. We present rigorous analysis for these two strategies and show their performance under MPEG-I and MPEG-II video streams playback rates. Their behavior under different network bandwidths is also examined, revealing in-depth information about their expected performance. We also show that in the case of a multi-installment strategy, the access time can be completely controlled by fine tuning the number of installments. Since the number of installments is software tunable, the adaptive nature of the strategies to different channel bandwidths is also demonstrated. Important trade-off studies with respect to the number of servers involved in the retrieval process and the number of installments are presented. In the case of a heterogeneous network employing a single-installment strategy, we prove that the access time is independent of the server sequence used. Illustrative examples are provided for ease of understanding.     

Evaluation of a comprehensive P2P video-on-demand streaming system

Video-on-demand (VoD) streaming has recently become a popular service on the Internet, with several companies offering videos to a global audience. However, traditional client/server based VoD streaming systems can be very bandwidth intensive and expensive to maintain, especially for high quality video content. To improve the scalability these systems, the use of peer-to-peer (P2P) networking has been proposed, but despite the efficiency of applications such as BitTorrent for downloading of large files, it is not simple to use P2P techniques for streaming. Problems such as firewalls and freeloaders reduce the efficiency of both types of P2P systems, but for real-time services such as streaming, the result can be reduced playback quality. Other issues include the traffic load imposed on ISPs by P2P networks, which can motivate ISPs to interfere with the P2P traffic. Finally, protecting against malicious modification of content can increase overhead, response times, and startup delays.We consider these issues to be fundamental to the problem of P2P based VoD, but despite the large amount of research that has been done in this field, these issues have largely been ignored. To address this, we present an evaluation of the Streaming P2P Protocol (SPP) architecture. By studying the problem as a whole we have found a simple and comprehensive solution that addresses all the four issues listed above. To show that the system is not only scalable, but also that it can be implemented efficiently, we have used both simulations and experiments on PlanetLab for evaluation. The results show that the combination of cache nodes and use of end-user resources found in the SPP architecture can give a low load on servers and ISPs, even when firewalls are taken into consideration. Furthermore, we observed low startup delays and few playback errors during the PlanetLab experiments. The scalable and low-cost distribution of content possible with the SPP architecture should be suitable for both large-scale commercial distributors and users of community networks with limited resources.     

中国高性能宽带信息网环境下视频点播业务模型

针对因特网无法提供电信级服务质量保证的问题,提出了中国高性能宽带信息网(3Tnet)环境下一种大规模视频点播(Video-on-Demand,VoD)业务模型.该模型适应实时播放及高清晰回放需求,在骨干网采用内容分发网络,在接入网采用P2P策略.讨论了该模型的可行性,给出了性能评估.仿真结果证明该模型支持3Tnet上大规模VoD业务.     

Multiple-server movie-retrieval strategies for distributed multimedia applications: a play-while-retrieve approach

In this paper, we present a generalized approach to retrieve a long-duration movie requested using a network-based video-on-demand service infrastructure employing multiple servers. We design and analyze a play-while-retrieve (PWR) playback strategy for this multiserver environment such that the access time (waiting time for the clients) is minimized. For this strategy, we use both the single-installment and multi-installment retrieval strategies to analyze the performance of the service system. For the above-mentioned retrieval strategies, we explicitly derive closed-form expressions for a minimum access time. For the case of multi-installment retrieval strategy, we conduct asymptotic performance analysis that quantifies the ultimate performance bounds of our strategy. We demonstrate analytically the impact of a large-scale network, as well as the impact of indefinitely increasing the number of installments, on the performance of such a multiserver service system. We then address the problem of buffer management at the client site, which is a closely related issue that has a significant influence on the performance of the strategy, and also serves as a key issue in making the service system attractive for clients. We derive relationships that quantify the minimum amount of buffer expected at the client site to have a smooth presentation with this multiserver service structure. Finally, we perform simulation experiments to verify all our theoretical findings. In the experiments, we compare the performance of PWR strategy with that of play-after-retrieve strategy, and discuss certain important points that are crucial for implementing a real-life working multiserver service system.     

Optimizing content placement in a peer-assisted VoD architecture

Recently, a new peer-assisted architecture to build content delivery systems has been presented. This architecture is based on the use of the storage capacity of end-users’ set-top boxes (STBs), connected in a peer-to-peer (P2P) manner in order to help the content servers in the delivery process. In these systems, the contents are usually split into a set of smaller pieces, called sub-streams, which are randomly injected at the STBs. The present paper is focused on Video on Demand (VoD) streaming and it is assumed that the STB-based content delivery system is deployed over the global Internet, where the clients are distributed over different ISP networks. In this scenario, three different strategies are studied for increasing the percentage of data uploaded by peers, in order to offload the content servers as much as possible. First of all, a new mechanism is presented which determines which sub-stream has to be placed at which STB by a Non-Linear Programming (NLP) formulation. A different strategy for reducing the content server load is to take advantage of the available bandwidth in the different ISP networks. In this sense, two new mechanisms for forwarding the VoD requests to different ISP networks are presented. Finally, the present paper also shows that in some situations the available uplink bandwidth is associated with STBs that do not have the required sub-streams. Regarding this concern, a new mechanism has been designed that dynamically re-allocates some streams, which are being transmitted from specific STBs, to different STBs, in order to find the necessary resources to start new streaming sessions.     

Rate-sensitive leverage of QoS and QoP for ubiquitous video streaming via buffer-aware feedback control

Providing real-time Internet video streaming anytime, anywhere and using any devices from different access networks preserves more challenges to equilibrate the quality of service (QoS) and security protection (QoP). Because encryption/decryption for video packets are time-consuming processes to protect real-time video streaming services from eavesdropping, our observation is that the playback buffer occupancy (PBO) can simply indicate time availability to adjust security level to affect the packet sending rate. In this paper, we present an end-to-end buffer-aware feedback control from client PBO for effectively securing media streaming for heterogeneous clients over ubiquitous Internet. That is, security-level adjustments can be applied further to keep PBO running away from overflow and underflow to pursue an effective leverage between QoS and QoP. To further boost the protection, we also apply the Diffie-Hellman key negotiation method to provide the dynamic key changes. Moreover, since the running PBO will vary on the dynamics of Internet from access time, client devices and access networks, the different applied security levels and key changes during the video streaming session will make eavesdropper more difficult to recover all the encrypted videos delivered in public networks. We demonstrate the leverage performance in preserving both QoS and QoP for ubiquitous video streaming in our proposed schemes by comprehensive experiments on a true VoD system. The experimental results show our secure VoD scheme can achieve cost-effective leverage of QoS and QoP from different inserted network dynamics, even if client buffer size is limited to 256 KB only.     

Zebroid: using IPTV data to support STB-assisted VoD content delivery

IPTV, unlike Internet TV, delivers digital TV and multimedia services over IP-based networks with the required level of quality of service (QoS) and quality of experience (QoE). Linear programming channels in IPTV are delivered through multicast, which is highly scalable with the number of subscribers. Video-on-demand (VoD) content, on the other hand, is typically delivered using unicast, which places a heavy load on the VoD servers and all the network components leading to the end-user set-top boxes (STBs) as the demand increases. With the rapid growth of IPTV subscribers and the shift in video viewing habits, the need to efficiently disseminate large volumes of VoD content has prompted IPTV service providers to consider the use of STBs to assist in video content delivery. This paper describes our current research work on Zebroid, a potential VoD solution for fiber-to-the-node (FTTN) networks, which uses IPTV data on a recurring basis to determine how to select, stripe, and preposition popular content in selected STBs during idle hours. A STB requesting VoD content during the peak hours can then receive necessary stripes from participating STBs in the neighborhood. Recent VoD request access patterns, STB availability data, and capacity data on network components are taken into consideration in determining the parameters used in the striping algorithm of Zebroid. We show both by simulation and emulation on a realistic IPTV testbed that the VoD server load can be reduced by more than 70% during peak hours by allocating only 8 GB of storage on each STB. The savings achieved through Zebroid would also allow IPTV service providers to add more linear programming channels without expensive infrastructure upgrades.     

InstantLeap: an architecture for fast neighbor discovery in large-scale P2P VoD streaming

In large-scale peer-to-peer (P2P) video-on-demand (VoD) streaming applications, a fundamental challenge is to quickly locate new supplying peers whenever a VCR command is issued, in order to achieve smooth viewing experiences. For many existing commercial systems which use tracker servers for neighbor discovery, the increasing scale of P2P VoD systems has overloaded the dedicated servers to the point where they cannot accurately identify the suppliers with the desired content and bandwidth. To avoid overloading the servers and achieve instant neighbor discovery over the self-organizing P2P overlay, we design a novel method of organizing peers watching a video. The method features a light-weight indexing architecture to support efficient streaming and fast neighbor discovery at the same time. InstantLeap separates the neighbors at each peer into a streaming neighbor list and a shortcut neighbor list, for streaming and neighbor discovery respectively, which are maintained loosely but effectively based on random neighbor list exchanges. Our analysis shows that InstantLeap achieves an O(1) neighbor discovery efficiency upon any playback “leap” across the media stream in streaming overlays of any size, and low messaging costs for overlay maintenance upon peer join, departure, and VCR operations. We also verify our design with large-scale simulation studies of dynamic P2P VoD systems based on real-world settings.     

Fast techniques for the optimal smoothing of stored video

Work-ahead smoothing is a technique whereby a server, transmitting stored compressed video to a client, utilizes client buffer space to reduce the rate variability of the transmitted stream. The technique requires the server to compute a schedule of transfer under the constraints that the client buffer neither overflows nor underflows. Recent work established an optimal off-line algorithm (which minimizes peak, variance and rate variability of the transmitted stream) under the assumptions of fixed client buffer size, known worst case network jitter, and strict playback of the client video. In this paper, we examine the practical considerations of heterogeneous and dynamically variable client buffer sizes, variable worst case network jitter estimates, and client interactivity. These conditions require on-line computation of the optimal transfer schedule. We focus on techniques for reducing on-line computation time. Specifically, (i) we present an algorithm for precomputing and storing the optimal schedules for all possible client buffer sizes in a compact manner; (ii) we show that it is theoretically possible to precompute and store compactly the optimal schedules for all possible estimates of worst case network jitter; (iii) in the context of playback resumption after client interactivity, we show convergence of the recomputed schedule with the original schedule, implying greatly reduced on-line computation time; and (iv) we propose and empirically evaluate an “approximation scheme” that produces a schedule close to optimal but takes much less computation time.     

一种嵌入式DSS客户端的架构设计及优化

达尔文流媒体服务器DSS(Darwin Streaming Server)因其良好的框架结构和开放性作为视频点播服务器广泛应用于各种流媒体系统中。本文基于嵌入式终端实现了一个DSS客户端,设计了该终端的体系架构,给出了多种媒体格式自适应支持以及提高用户体验的VCR操作的方法,并在性能上进行了优化。     

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。     

An active buffer management technique for providing interactive functions in broadcast video-on-demand systems

Multicast delivery is an efficient approach to the provision of a video-on-demand (VoD) service. Interacting with the video stream is a desirable feature for users. However, it is a challenging task to provide the functionality in the multicast environment because a lot of users share multicast delivery channels. In this paper, we propose an active buffer management technique to provide interactive functions in broadcast VoD systems. In our scheme, the client can selectively prefetch segments from broadcast channels based on the observation of the play point in its local buffer. The content of the buffer is adjusted in such a way that the relative position of the play point is kept in the middle part of the buffer. Our simulations show that the active buffer management scheme can implement interactive actions through buffering with a high probability in a wide range of user interaction levels.     

A VoD Application Implemented in Java

This article describes an implementation of a Video-on-Demand (VoD) system for the VoD interoperability test laboratory of the National Institute of Standards and Technology. It describes how Java can be used to implement the client side of a DAVIC based client-server system, which consists of a video server and a Set-Top Unit (STU) client. The communication between the video server and the STU is based on the Digital Storage Media Command and Control (DSM-CC) protocols. The VoD application is defined as a set of Java classes. These classes implement the graphical interfaces for user navigation and control. While this system is compliant with DAVIC specifications, it also permits an elegant integration of DAVIC services to the Internet environment.     

An Efficient Scheduling Algorithm for Information Delivery on VoD System

Minimizing transmission and storage cost for delivering video programs is an important aspect of video-on-demand (VoD) systems. Since the size of data is quite large, caching programs at cheap storage sites for future delivery can be very beneficial. In this paper, we propose a scheduling algorithm to aim directly on VoD systems under the metropolitan-area network. By mapping any delivery schedule into a connected path under a special weighted graph, the original scheduling problem can be reduced to the optimal Steiner tree problem. After analyzing the characteristics of the Steiner tree under the special graph, we introduce the concept of potential value and then formulate the cost of each Steiner tree as an equation of potential value. We can hence obtain the cost of each delivery schedule through calculating the corresponding equation of the potential value. Therefore, by comparing the cost of any possible Steiner tree, we can eventually find the optimal total cost for servicing all requests. Also, the time complexity of our algorithm is O(m ³ n ²), where m is the number of servers and n is the number of requests.