Performance model of interactive video-on-demand systems

A large scale, distributed video-on-demand (VOD) system allows geographically dispersed residential and business users to access video services, such as movies and other multimedia programs or documents on demand from video servers on a high speed network. In this paper we demonstrate through analysis and simulation the need for a hierarchical architecture for the video-on-demand distribution network. We assume a hierarchical architecture, which fits the existing tree topology used in today's cable TV (CATV) hybrid fiber/coaxial (HFC) distribution networks. We develop a model for the design, configuration, program placement and performance evaluation of such systems. The model takes into account the user behavior, the fact that the user re quests are transmitted over a shared channel before reaching the video server containing the requested program, the finite input/output (I/O) capacity of the video servers, the exponential storage cost of the multimedia programs imposed by the adopted architecture of the video-on-demand distribution network, and finally the communication cost. In addition, our model allows batching of user requests at the video server and we study the effect of batching on the performance of the video server and on the delivered to the user Quality of Service (QoS). The design and evaluation is based on an extensive analytical and simulation study. The results in this paper contribute to the understanding of the tradeoffs between quality of service, server I/O, storage required, program placement, and commu nication cost. They are helpful in configuring the VOD dis tribution network, optimally placing the programs across the hierarchy of the video servers, and maximizing the performance of the overall system.

Previously proposed streaming protocols using broadcast or multicast are able to deliver multimedia files on-demand with required server bandwidth that grows much slower than linearly with request rate, or with the inverse of client start-up delay. The same efficiencies can be achieved for network bandwidth if delivery is over a true broadcast channel. This paper considers the required network bandwidth for on-demand streaming over multicast delivery trees. We consider both simple canonical delivery trees, and more complex cases in which delivery trees are constructed using both existing and new algorithms for randomly generated network topologies and client site locations. Results in this paper quantify the potential savings from use of multicast trees that are configured to minimize network bandwidth rather than the latency to the content server. Further, we determine the network bandwidth usage of particular immediate service and periodic broadcast on-demand streaming protocols. The periodic broadcast protocol is able to simultaneously achieve close to the minimum possible network and server bandwidth usage.

In a video-on-demand (VOD) system, it is desirable to provide the user with interactive browsing functions such as “fast forward” and “fast backward.” However, these functions usually require a significant amount of additional resources from the VOD system in terms of storage space, retrieval throughput, network bandwidth, etc. Moreover, prevalent video compression techniques such as MPEG impose additional constraints on the process since they introduce inter-frame dependencies. In this paper, we devise methods to support variable rate browsing for MPEG-like video steams and minimize the additional resources required. Specifically, we consider retrieval for a disk-array-based video server and address the problem of distributing the retrieval requests across the disks.Our overall approach for interactive browsing comprises (1) a storage method, (2) placement and sampling methods, and (3) a playout method, where the placement and sampling methods are two alternatives for video segment selection. The segment sampling scheme supports browsing at any desired speed, while minimizing the variation on the number of video segments skipped between samplings. On the other hand, the segment placement scheme supports completely uniform segment sampling across the disk array for some specific speedup rates. Experiments for the visual effect of the proposed segment skipping approach have been conducted on MPEG data. It is shown that the proposed method is a viable approach to video browsing.

The received quality of the video contents streamed over Video on Demand (VOD) networks is easily degraded by interference and other external factors during the encoding and transmission stages. However, the service provider generally bills the subscriber in accordance with the original fee, irrespective of the actual video quality received. Consequently, the subscribers’ rights are infringed and their dissatisfactions increased. To address this problem, the present study outlines a VOD billing method in which the video quality at the receiver end is evaluated using a watermarking scheme, and the fee charged by the service provider is then adjusted accordingly. The basic feasibility of the proposed approach is demonstrated by means of simulations using standard test video sequences. The results show that the watermarking scheme provides an effective means of evaluating the video quality at the receiver end, and thus provides a reliable basis for quality-dependent subscriber billing in VOD systems. Moreover, the watermarking scheme also reduces the size of the watermarked file. As a result, both the storage space requirement at the video server and the server network bandwidth requirement are reduced. Consequently, the proposed system provides a win-win solution for the subscribers and service providers in VOD systems.

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.

In a video-on-demand (VOD) environment, disk arrays are often used to support the disk bandwidth requirement. This can pose serious problems on available disk bandwidth upon disk failure. In this paper, we explore the approach of replicating frequently accessed movies to provide high data bandwidth and fault tolerance required in a disk-array-based video server. An isochronous continuous video stream imposes different requirements from a random access pattern on databases or files. Explicitly, we propose a new replica placement method, called rotational mirrored declustering (RMD), to support high data availability for disk arrays in a VOD environment. In essence, RMD is similar to the conventional mirrored declustering in that replicas are stored in different disk arrays. However, it is different from the latter in that the replica placements in different disk arrays under RMD are properly rotated. Combining the merits of prior chained and mirrored declustering methods, RMD is particularly suitable for storing multiple movie copies to support VOD applications. To assess the performance of RMD, we conduct a series of experiments by emulating the storage and delivery of movies in a VOD system. Our results show that RMD consistently outperforms the conventional methods in terms of load-balancing and fault-tolerance capability after disk failure, and is deemed a viable approach to supporting replica placement in a disk-array-based video server.

As computer and network technology advance, multimedia data can be transferred in real time on the Internet. The increasing user demands for various multimedia data make VOD (Video-on-Demand) services to be developed. VOD services are being used in lots of fields, such as entertainment, distance learning, home shopping, and interactive news. In comparison to the existing HTTP services, these VOD services have special features that the time for their services is longer and the services request more disks and network bandwidths. Therefore, compared to HTTP service environments, VOD services have some different workload patterns. In these VOD service environments, the existing load balancing algorithms researched before are not proper. In this paper, we propose a new load balancing algorithm that is based on the history of past user access patterns to make server loads even on hierarchically distributed VOD system environments. This algorithm uses a dynamic genetic algorithm. The proposed distributed VOD system environment consists of a number of VOD servers, which are distributed geographically, and control servers that manage each group of VOD servers. User requests are distributed to prevent convergence by distributing VOD servers geographically. We use a genetic algorithm based on history data to distribute user requests in a local service area. The information of user requests and services is stored and referred in a database as history data. By applying these history data to the fitness function of genetic algorithms, we implemented the genetic algorithm and operations for VOD systems. The load balancing algorithm proposed in this paper can distributed workloads by predicting workloads precisely on VOD environments.

This article describes video on demand (VOD) and near video on demand (NVOD) and explains the differences between the various types of VOD systems as they relate to telephone company (Telco), commmunity antenna or cable television (CATV), cellular TV, and hotel applications. System similarities of the various carriers are described, with the intent to identify as much common equipment as possible that will be compatible across the various applications. Basic VOD functional requirements are also discussed. Hotel VOD systems are really small CATV or Telco systems that can be expanded into full-size, commercially viable VOD systems easily because of their scalable architecture. The roles of image compression, video-friendly disk-storage systems, video servers, encryption, switching, transmission, and control-system elements in this VOD application are also discussed.

A design for a video service engine (VSE) with a small computer system interface (SCSI) is proposed. It is implemented to an ADSL-based near video on demand (NVOD) system as the video stream pump to provide interactive services. The description of the VSE follows the sequence of system overview, hardware architecture and operation flow control in order to give a comprehensive understanding of it. In addition, a video service trial which uses the VSE to pump 504 channels of program at the DS1 rate is also introduced. From the quality of service (QoS) test, the VSE successfully provides interactive service to the customer with a distance of 15000 feet from the central office. Hence, a reliable video delivery system with good quality is proved.

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.

Summary form only given. We present an implementation of a VOD (video on demand) system that addresses the problem of increasing video stream supply capabilities. To obtain fundamental video stream transfer characteristics on Ethernet, we first performed an experiment in which it became clear that bottlenecks of the CPU of a video server were the most serious. To solve this problem we implemented a distributed RAID4 (Redundant Arrays of Inexpensive Disks) method video server. Distributed RAID means extending the RAID method usually applied to disks to the servers, so as to achieve improvements in performance and reliability. The great advantage of this architecture is that the linear performance improvement can be achieved by adding inexpensive servers of a diffusion model.

Video-on-demand (VoD) is a service that has received much attention recently and the concept has become popular with computer and communication companies. Basically, VoD consists of a video server, interconnection network and user display equipment (UDE). It provides a similar service to the neighbourhood rental store. Videos or movies are distributed from the video server to users upon request through the network and users can view interactively using their UDE along with VCR-like functions (e.g. forward, rewind, pause and resume). VoD offers a convenient service since users do not have to leave their homes, which also leads to shorter response times than with today’s video stores. One important aspect of any VoD is the storage scheme used, which affects the amount and type of storage required, the maximum number of concurrent video streams and the average waiting time experienced by users of the service from the moment they choose a video to the moment video playback starts. The paper reviews some well known storage schemes, such as the phase based method and the phase based with replication method, and then proposes two new schemes that further increase the number of concurrent streams and reduce the waiting time, while reducing the total storage space required. These new schemes rely on two concepts called immediate playback RAM and sustainable playback storage. Using a case study, the new schemes are briefly compared with an existing scheme and their strengths and shortcomings are highlighted. Using some typical values, analyses are carried out that quantify the performance gain resulting from the new storage schemes.

Recent advances in the construction of broadcast schedules allow the bandwidth-efficient distribution of Variable Bit Rate (VBR) encoded video. Furthermore, most users are no longer severely limited by their local storage requirements, but are still limited in terms of available bandwidth. We examine an architecture that allows scalable video-on-demand (VoD) delivery, given bandwidth restrictions along the path from the distribution (video server) point to the user access point. We assume the use of a reservation scheme, such as RSVP, and we describe how a protocol based on a VoD broadcast algorithms can be deployed over a reservation- and multicast-capable Internet.

The main mechanism of Video on Demand (VoD) system is based on the balance between the need from customs and the system resources. To guarantee high quality of services, VoD systems can employ admission control schemes to decide whether a new request for resource services will be offered or not. In this paper, an admission control algorithm is proposed to improve the performance of the VoD system by using a different probability method. The proposed admission control algorithm was simulated on NS2 platform. Simulation experimental results show that the proposed admission control algorithm in this paper is characterized by better reducing the blockage for the VoD system.

The MPEG committee standardized the MPEG AVC (H.264) video coding standard in May 2003. The standard has since seen strong interest and adoption from the industry. A competing standard developed by Microsoft, referred to as VC-1, was standardized in SMPTE in April 2006. VC-1 is essentially a standardized version of Microsoft's Windows Media Video (WMV-9). Both H.264 and VC-1 are highly efficient compression standards that enable high-quality video services such as IPTV and Blu-ray Disc. H.264 and VC-1 are both mandated for high definition video services on Blu-ray Disc. These two standards are expected to form the basis for a new generation of high-quality broadband video services. The VC-1 and H.264 Video Compression Standards for Broadband Video Services covers these video coding standards, as well as issues in broadband video delivery. No other book about H.264 or VC-1 covers the standards in such detail. This book interprets the complex standards specifications and makes these new technologies accessible. Both authors have more than 12 years experience working on video compression and communications. The VC-1 and H.264 Video Compression Standards for Broadband Video Services is designed for researchers and a professional audience, including video engineers, and practitioners in consumer electronics, telecommunications and media compression industries. This book is also suitable as a secondary text or reference for advanced-level students in computer science and electrical engineering.