Continuous Media Server Research Articles

Streaming of Continuous Media for Distance Education Systems

Distance education created new challenges regarding the delivery of large size isochronous continuous streaming media (SM) objects. In this paper, we consider the design of a framework for customized SM presentations, where each presentation consists of a number of SM objects that should be retrieved and displayed to the user in a coherent fashion. We describe a retrieval optimizer (Prime) that captures the flexibilities and requirements imposed by the user query, user profile, and session profile. Then, it determines how this query script should be imposed against the continuous media (CM) server to reduce contention. We also provide a cost model to evaluate each proposed plan. Finally, we explain the role of memory buffering in alleviating the server bandwidth fragmentation problem. Our preliminary experimental results show the feasibility and effectiveness of our proposed model and techniques in generating near optimal retrieval.

A multi-threshold online smoothing technique for variable rate multimedia streams

Variable bit rate (VBR) compression for media streams allocates more bits to complex scenes and fewer bits to simple scenes. This results in a higher and more uniform visual and aural quality. The disadvantage of the VBR technique is that it results in bursty network traffic and uneven resource utilization when streaming media. In this study we propose an online media transmission smoothing technique that requires no a priori knowledge of the actual bit rate. It utilizes multi-level buffer thresholds at the client side that trigger feedback information sent to the server. This technique can be applied to both live captured streams and stored streams without requiring any server side pre-processing. We have implemented this scheme in our continuous media server and verified its operation across real world LAN and WAN connections. The results show smoother transmission schedules than any other previously proposed online technique.

Scalable and fault-tolerant support for variable bit-rate data in the exedra streaming server

We describe the design and implementation of the Exedra continuous media server, and experimentally evaluate alternative resource management policies using a prototype system that we built. Exedra has been designed to provide scalable and efficient support for variable bit-rate media streams whose compression efficiency leads to reduced storage space and bandwidth requirements in comparison to constant bit-rate streams of equivalent quality. We examine alternative disk striping policies, and quantify the benefits of innovative techniques for storage space allocation, buffer management, and resource reservation, which we developed to achieve both predictability and high-performance in handling disk and network data transfers of variable size. Additionally, we investigate the differences between diverse data replication schemes over disk arrays, and compare methods for disk access time reservation that enable tolerance of disk failures at minimal cost. Overall, we demonstrate the feasibility of building network media servers that exploit the latest advances in media compression technology towards reducing the cost of wide-scale streaming services for stored data.

Development and evolution of a heterogeneous continuous media server: a case study: Practice Articles

Media server software is significantly complicated to develop and maintain, due to the nature of the many interface aspects which must be considered. This paper provides a case study of the design, implementation, and evolution of a continuous media file server. We place emphasis on the evolution of the software and our approach to maintainability. The user interface is a major consideration, even though the server software would appear isolated from that factor. Since continuous media servers must send the raw data to a client application over a network, the protocol considerations, hardware interface, and data storage/retrieval methods are of the paramount importance. In addition, the application programmer's interface to the server facilities has an impact on both the internal design and the performance of such a server. We discuss our experiences and insight into the development of such software products within a small research-based university environment. We experienced two main types of evolutionary change: requirements changes from the limited user community and performance enhancements/corrections. While the former were anticipated via a generic interface and modular design structure, the latter were surprising and substantially more difficult to solve. Copyright © 2005 John Wiley & Sons, Ltd.

Development and evolution of a heterogeneous continuous media server: a case study

Media server software is significantly complicated to develop and maintain, due to the nature of the many interface aspects which must be considered. This paper provides a case study of the design, implementation, and evolution of a continuous media file server. We place emphasis on the evolution of the software and our approach to maintainability. The user interface is a major consideration, even though the server software would appear isolated from that factor. Since continuous media servers must send the raw data to a client application over a network, the protocol considerations, hardware interface, and data storage/retrieval methods are of the paramount importance. In addition, the application programmer's interface to the server facilities has an impact on both the internal design and the performance of such a server. We discuss our experiences and insight into the development of such software products within a small research-based university environment. We experienced two main types of evolutionary change: requirements changes from the limited user community and performance enhancements/corrections. While the former were anticipated via a generic interface and modular design structure, the latter were surprising and substantially more difficult to solve. Copyright © 2005 John Wiley & Sons, Ltd.

Optimal Cache Memory Exploitation for Continuous Media: To Cache or to Prefetch?

Network continuous-media applications are emerging with a great pace. Cache memories have long been recognized as a key resource (along with network bandwidth) whose intelligent exploitation can ensure high performance for such applications. Cache memories exist at the continuous-media servers and their proxy servers in the network. Within a server, cache memories exist in a hierarchy (at the host, the storage-devices, and at intermediate multi-device controllers). Our research is concerned with how to best exploit these resources in the context of continuous media servers and in particular, how to best exploit the available cache memories at the drive, the disk array controller, and the host levels. Our results determine under which circumstances and system configurations it is preferable to devote the available memory to traditional caching (a.k.a. “data sharing”) techniques as opposed to prefetching techniques. In addition, we show how to configure the available memory for optimal performance and optimal cost. Our results show that prefetching techniques are preferable for small-size caches (such as those expected at the drive level). For very large caches (such as those employed at the host level) caching techniques are preferable. For intermediate cache sizes (such as those at multi-device controllers) a combination of both strategies should be employed.

Controlled Buffer Sharing in Continuous Media Servers

Continuous media servers manage delay sensitive data such as audio and video clips. Once a server initiates the display of a clip on behalf of a client, it must deliver the data to the client in a manner that prevents data starvation. Otherwise, its display may suffer from disruptions and delays, termed hiccups. A hiccup-free display is important to a number of applications such as video-on-demand for entertainment, distance learning, news dissemination, etc. Buffer sharing enables a server to trade memory for disk bandwidth to service multiple clients by sharing data in memory, using a single disk stream. However, an uncontrolled buffer sharing scheme may reduce system performance. This paper presents Controlled Buffer Sharing (CBS) as a novel framework that facilitates sharing and supports both a hiccup-free display and VCR operations. It includes a configuration planner and a buffer pool management technique (applied at run time). CBS trades memory for disk bandwidth in order to meet the performance objectives of an application and minimize cost per stream. It uses bridging and merges two displays referencing the same clip when they are dt blocks apart. One insight of this framework is that dt is determined by market forces (cost of memory and disk bandwidth) and is independent of a clip's frequency of access. We use both analytical and simulation models to quantify the characteristics of CBS.

A New Block Fetching Scheme Considering Traffic Smoothing in Multimedia Servers

Typical block placement schemes generally assume CTL (Constant Time Length) block size, one block read for each stream in a round, round-robin striping, and peak rate-based admission control. Traditional smoothing schemes for stored continuous media objects do not consider the block layout of the storage system. Hence, the combination of schemes from the two domains can introduce new challenges. In this paper, we present a server transmission delay problem that arises when traditional block placement and smoothing schemes are used at the same time in a continuous media server. To resolve the problem, we first present two simple straightforward solutions, Server-side Block Prefetching and Multiple Block Read, and then propose a new solution Smoothed Fetching. SF overcomes the defects of the other two schemes by exploiting a smoothing technique when retrieving blocks from disks and using a tight admission control algorithm. Simulation results show that SF achieves the best performance among the three solutions.

Storing continuous media objects to multizone recording disks using multirate smoothing technique

Since multizone recording disks have different bandwidths and capacities depending on the zone in use, data placement schemes for traditional constant angular density disks are not suitable for multizone recording disks. In this paper, we propose a new block placement algorithm for multizone recording disks used for continuous media servers. The proposed scheme exploits the bandwidth-saving effect of smoothing variable bit rate data before storing them. The diversity of zone bandwidths in multizone recording disks enables it possible to achieve large smoothing effect using relatively small buffer space. Variable bit rate data blocks of an object are smoothed using multiple smoothing rates which are bandwidths of zones multiplied by the service time assigned to the object and are stored into the corresponding zones. This multirate smoothing technique decreases the buffer space required to provide deterministic service to clients. Simulation results show that a proper restructuring of blocks according to the smoothing algorithm results in dramatic performance enhancement in continuous media servers.

Modeling the Caching Effect in Continuous Media Servers

Caching is one of the most important schemes for improving the performance of continuous media servers. Continuous object caching enables a server to support more clients simultaneously since it reduces the disk load imposed at each round. However, without a quantative analysis of the disk load reduction induced by caching, the caching effect can not be reflected in the admission control scheme, which limits the number of simultaneous clients serviced. In this paper, we define a performance metric for caching scheme in the continuous media server, define an optimal caching, formalize three heuristic block replacement model and propose a novel near optimal caching scheme. For quantative analysis of the proposed scheme we also propose a probabilistic model of the caching effect in a continuous media server. The proposed model enables the development of efficient statistical admission control algorithms that can increase the number of clients serviced simultaneously. To show the potential of the model, we present a simple example of a statistical admission control algorithm and demonstrate the performance enhancement resulting from the use of the proposed model.

A Statistical Admission Control Scheme for Continuous Media Servers Using Caching

In continuous media servers, disk load can be reduced by using buffer cache. In order to utilize the saved disk bandwidth by caching, a continuous media server must employ an admission control scheme to decide whether a new client can be admitted for service without violating the requirements of clients already being serviced. A scheme providing deterministic QoS guarantees in servers using caching has already been proposed. Since, however, deterministic admission control is based on the worst case assumption, it causes the wastage of the system resources. If we can exactly predict the future available disk bandwidth, both high disk utilization and hiccup-free service are achievable. However, as the caching effect is not analytically determined, it is difficult to predict the disk load without substantial computation overhead. In this paper, we propose a statistical admission control scheme for continuous media servers where caching is used to reduce disk load. This scheme improves disk utilization and allows more streams to be serviced while maintaining near-deterministic service. The scheme, called Shortsighted Prediction Admission Control (SPAC), combines exact prediction through on-line simulation and statistical estimation using a probabilistic model of future disk load in order to reduce computation overhead. It thereby exploits the variation in disk load induced by VBR-encoded objects and the decrease in client load by caching. Through trace-driven simulations, it is demonstrated that the scheme provides near-deterministic QoS and keeps disk utilization high.

Clustered Scheduling Algorithms for Mixed-Media Disk Workloads in a Multimedia Server

Divisible load scenarios occur in modern media server applications since most multimedia applications typically require access to continuous and discrete data. A high performance Continuous Media (CM) server greatly depends on the ability of its disk IO subsystem to serve both types of workloads efficiently. Disk scheduling algorithms for mixed media workloads, although they play a central role in this task, have been overlooked by related research efforts. These algorithms must satisfy several stringent performance goals, such as achieving low response time and ensuring fairness, for the discrete-data workload, while at the same time guaranteeing the uninterrupted delivery of continuous data, for the continuous-data workload. The focus of this paper is on disk scheduling algorithms for mixed media workloads in a multimedia information server. We propose novel algorithms, present a taxonomy of relevant algorithms, and study their performance through experimentation. Our results show that our algorithms offer drastic improvements in discrete request average response times, are fair, serve continuous requests without interruptions, and that the disk technology trends are such that the expected performance benefits can be even greater in the future.

Decentralized resource management for a distributed continuous media server

Distributed continuous media server (DCMS) architectures are proposed to minimize the communication-storage cost for those continuous media applications that serve a large number of geographically distributed clients. Typically, a DCMS is designed as a pure hierarchy (tree) of centralized continuous media servers. In an earlier work, we proposed a redundant hierarchical topology for DCMS networks, termed RedHi, which can potentially result in higher utilization and better reliability over pure hierarchy. We focus on the design of a resource management system for RedHi that can exploit the resources of its DCMS network to achieve these performance objectives. Our proposed resource management system is based on a fully decentralized approach to achieve optimal scalability and robustness. In general, the major drawback of a fully decentralized design is the increase in latency time and communication overhead to locate the requested object. However, as compared to the typically long duration and high resource/bandwidth requirements of continuous media objects, the extra latency and overhead of a decentralized resource management approach become negligible. Moreover, our resource management system collapses three management tasks: (1) object location, (2) path selection, and (3) resource reservation, into one fully decentralized object delivery mechanism, reducing the latency even further. In sum, decentralization of the resource management satisfies our scalability and robustness objectives, whereas collapsing the management tasks helps alleviate the latency and overhead constraints.

Decentralized resource management for a distributed continuous media server

Distributed continuous media server (DCMS) architectures are proposed to minimize the communication-storage cost for those continuous media applications that serve a large number of geographically distributed clients. Typically, a DCMS is designed as a pure hierarchy of centralized continuous media servers. RedHi, a Redundant Hierarchical topology for DCMS networks, can result in higher utilization and better reliability over pure hierarchy. We focus on the design of a resource management system (RMS) for RedHi that can exploit the resources of its DCMS network to achieve these performance objectives. Our RMS is based on a fully decentralized approach to achieve optimal scalability and robustness. The major drawback of a fully decentralized design is the increase in latency time and communication overhead to locate the requested object. However, as compared to the typically long duration and high resource/bandwidth requirements of continuous media objects, the extra latency and overhead of a decentralized resource management approach become negligible. Moreover, our RMS collapses three management tasks (object location, path selection and resource reservation) into one fully decentralized object delivery mechanism, reducing the latency even further. Decentralization of the resource management satisfies our scalability and robustness objectives, whereas collapsing the management tasks helps alleviate the latency and overhead constraints. To achieve a high resource utilization, the object delivery scheme uses our proposed cost function, as well as various object location and resource reservation policies to select and allocate the best streaming path to serve each request. The object delivery scheme is designed as an application-layer resource management middleware for the DCMS architecture to be independent of the underlying telecommunication infrastructure. Experiments show that our RMS is successful in realization of the higher resource utilization for the DCMS networks with the RedHi topology.

Yima: a second-generation continuous media server

Continuous media data requires a streaming architecture that can manage real-time delivery constraints and address the large size of CM objects. Although commercial systems ordinarily use proprietary technology and algorithms, making it difficult to compare their products with research prototypes, the authors have designed and developed Yima, a second-generation CM server that demonstrates several advanced concepts. Although this system has not yet achieved the refinement of commercial solutions, it is operational and incorporates lessons learned from first-generation research prototypes, including complete distribution, efficient online scalability, and synchronization of several media streams within a single frame. The paper discusses the multinode server architecture.

QoS-adaptive bandwidth scheduling in continuous media streaming

In this paper, we present a QoS-adaptive admission control and resource scheduling framework for continuous media (CM) servers. The framework consists of two parts. One is a reserve-based admission control mechanism in which new streams, arriving during periods of congestion, are offered lower QoS, instead of being blocked. The other part is a scheduler for continuous media with dynamic resource allocation to achieve higher utilization than non-dynamic schedulers by effectively sharing available resources among contending streams and by reclamation which is a scheduler-initiated negotiation to reallocate resources among streams to improve overall QoS. This soft-QoS framework recognizes that CM applications can generally tolerate certain variations on QoS parameters; that is, it exploits the findings about human tolerance to degradation in quality of multimedia streams. Using our policy, we could increase the number of simultaneously running clients that could be supported and could ensure a good response ratio and better resource utilization under heavy traffic requirements. Our admission control and scheduling strategy provides three principle advantages over conventional mechanisms. First, it guarantees better total system utilization. Second, it provides better disk utilization and larger admission ratio for input CM streams, which is a major advantage. Third, it still presents acceptable play-out qualities compared to the conventional greedy admission control algorithm.

Automatic recovery from disk failure in continuous-media servers

Continuous-media (CM) servers have been around for some years. Apart from server capacity, another important issue in the deployment of CM servers is reliability. This study investigates rebuild algorithms for automatically rebuilding data stored in a failed disk into a spare disk. Specifically, a block-based rebuild algorithm is studied with the rebuild time and buffer requirement modeled. A buffer-sharing scheme is then proposed to eliminate the additional buffers needed by the rebuild process. To further improve rebuild performance, a track-based rebuild algorithm that rebuilds lost data in tracks is proposed and analyzed. Results show that track-based rebuild, while it substantially outperforms block-based rebuild, requires significantly more buffers (17-135 percent more) even with buffer sharing. To tackle this problem, a novel pipelined rebuild algorithm is proposed to take advantage of the sequential property of track retrievals to pipeline the reading and writing processes. This pipelined rebuild algorithm achieves the same rebuild performance as track-based rebuild, but reduces the extra buffer requirement to insignificant levels (0.7-1.9 percent). Numerical results computed using models of five commercial disk drives demonstrate that automatic rebuild of a failed disk can be done in a reasonable amount of time, even at relatively high server utilization (e.g., less than 1.5 hours at 90 percent utilization).

비디오 서버에서의 효율적인 대역폭 스케줄링 지원

멀티미디어 어플리케이션들은 기존의 화일 서버 기법으로는 쉽게 제공하지 못하는 보장된 검색 및 전송률을 요구한다. 본 논문에서는 CM(Continuous Media : 예를 들어 비디오) 서버를 위한 동적 협상 수락 제어(dynamic negotiated admission control)와 자원 스케줄링(resource scheduling) 기법을 제안한다. 이는 두 부분으로 구성되는데, 예약 기반 수락 제어 방법(reserve-baed admission control mechanism)과 동적으로 자원을 할당하는 스케줄러가 그것이다. 정적 스케줄러와 비교할 때, 제안된 기법은 경쟁하는 스트림들에게 이용가능 한 자원들을 효과적으로 공유할 수 있도록 해주며, 전반적인 QoS(Quality of Service)를 향상시키기 위해 자원의 재 할당을 요구하는 스트림들을 위한 스케줄러 초기화 협상(scheduler-initiated negotation)을 통해 높은 이용률을 얻을 수 있다. 본 논문에서 제안한 기법을 사용하여 동시에 실행시킬 수 있는 클라이언트의 수를 증가시킬 수 있으며 혼잡한 트래픽 상태에서도 좋은 응답 비율과 향상된 자원 이용률을 얻을 수 있다. Continuous multimedia applications require a guaranteed retricval and transfer rate of streaming data, which conventional file server mechanism generally does not provide. In this paper we describe a dynamic negotiated admission control and dick bandwidth scheduling framework for Continuous Media (CM : e.g., video) servers. The framework consists of two parts. One is a reserve-based admission control mechanism and the other part is a scheduler for continuous media streams with dynamic resource allocation to achieve higher utilization than non-dynamic scheduler by effectively sharing available resources among contending streams to improve overall QoS. Using our policy, we could increase the number of simultaneously running: clients that coo]d be supported and cot]d ensure a good response ratio and better resource utilization under heavy traffic requirements.

Design of Scalable Continuous Media Servers

Multimedia applications place high demands for quality-of-service (QoS), performance, and reliability on systems. These stringent requirements make design of cost-effective and scalable systems difficult. Therefore efficient adaptive and dynamic resource management techniques in conjunction with data placement techniques can be of great help in improving performance, scalability, and reliability of such systems. This is the focus of our paper.

QoS-based evaluation of file systems and distributed system services for continuous media provisioning

This paper presents a QoS-based performance analysis of file systems and distributed object services for Continuous Media (CM) provisioning, as well as the details and implementation experiences of a continuous media file system and associated CM servers. For this we have implemented QoS-driven CM servers and the Presto continuous media file system (PFS) in the context of a distributed multimedia application development environment, and validate the performance of PFS against that of the conventional Unix file system through an experimental evaluation. Using our CM server prototype, we next examine the effect of continuous media data delivery on the three different kinds of network protocols such as CORBA, UDP/IP, and TCP/IP, with respect to QoS provisioning and throughput.