Yuewei Wang

Video staging: a proxy-server-based approach to end-to-end video delivery over wide-area networks

Real-time distribution of stored video over wide-area networks (WANs) is a crucial component of many emerging distributed multimedia applications. The heterogeneity in the underlying network environments is an important factor that must be taken into consideration when designing an end-to-end video delivery system. We present a novel approach to the problem of end-to-end video delivery over WANs using proxy servers situated between local-area networks (LANs) and a backbone WAN. A major objective of our approach is to reduce the backbone WAN bandwidth requirement. Toward this end, we develop an effective video delivery technique called video staging via intelligent utilization of the disk bandwidth and storage space available at proxy servers. Using this video staging technique, only part of a video stream is retrieved directly from the central video server across the backbone WAN whereas the rest of the video stream is delivered to users locally from proxy servers attached to the LANs. In this manner, the WAN bandwidth requirement can be significantly reduced, particularly when a large number of users from the same LAN access the video data. We design several video staging methods and evaluate their effectiveness in trading the disk bandwidth of a proxy server for the backbone WAN bandwidth. We also develop two heuristic algorithms to solve the problem of designing a multiple video staging scheme for a proxy server with a given video access profile of a LAN. Our results demonstrate that the proposed proxy-server-based approach provides an effective and scalable solution to the problem of the end-to-end video delivery over WANs.

A network-conscious approach to end-to-end video delivery over wide area networks using proxy servers

In this paper we present a novel network-conscious approach to the problem of end-to-end video delivery over wide-area networks using proxy servers situated between local-area networks (LANs) and a backbone wide-area network (WAN). We develop a novel and effective video delivery technique called video staging via intelligent utilization of the disk bandwidth and storage space available at proxy servers. We also design several video staging methods and evaluate their effectiveness in reducing the backbone WAN bandwidth requirement. Our results demonstrate that the proposed proxy-server-based, network-conscious approach provides an effective and scalable solution to the problem of the end-to-end video delivery over wide-area networks.

Weighted striping in multimedia servers

To cope with the increasing demand of customers, more magnetic disks may need to be added to a multimedia server to support a higher number of concurrent accesses. Due to the rapid improvement in the performance of magnetic disks, the newly added disks usually have higher sustained I/O bandwidth and bigger storage capacity. The traditional uniform striping in an environment with heterogeneous disks in the same striping group cannot fully utilize the I/O bandwidth and storage capacity of the newly added, higher performance disks. In this paper, we propose weighted striping techniques to fully utilize the I/O bandwidth and storage capacity of higher performance disks in a multimedia server. Our results show that weighted striping techniques greatly improve the performance of multimedia servers.

Efficient video file allocation schemes for video-on-demand services

Abstract. A video-on-demand (VOD) server needs to store hundreds of movie titles and to support thousands of concurrent accesses. This, technically and economically, imposes a great challenge on the design of the disk storage subsystem of a VOD server. Due to different demands for different movie titles, the numbers of concurrent accesses to each movie can differ a lot. We define access profile as the number of concurrent accesses to each movie title that should be supported by a VOD server. The access profile is derived based on the popularity of each movie title and thus serves as a major design goal for the disk storage subsystem. Since some popular (hot) movie titles may be concurrently accessed by hundreds of users and a current high-end magnetic disk array (disk) can only support tens of concurrent accesses, it is necessary to replicate and/or stripe the hot movie files over multiple disk arrays. The consequence of replication and striping of hot movie titles is the potential increase on the required number of disk arrays. Therefore, how to replicate, stripe, and place the movie files over a minimum number of magnetic disk arrays such that a given access profile can be supported is an important problem. In this paper, we formulate the problem of the video file allocation over disk arrays, demonstrate that it is a NP-hard problem, and present some heuristic algorithms to find the near-optimal solutions. The result of this study can be applied to the design of the storage subsystem of a VOD server to economically minimize the cost or to maximize the utilization of disk arrays.

Two Emerging Serial Storage Interfacesfor Supporting Digital Libraries: Serial Storage Architecture(SSA) and Fiber Channel-Arbitrated Loop (FC-AL)

Digital libraries require not only high storage space capacity but also high performance storage systems which provide the fast accesses to the data. These requirements can not be efficiently supported with the traditional SCSI interfaces. Several serial storage interfaces have been proposed for constructing storage systems with high transfer bandwidth, large storage capacity, and fault tolerance feature. Among them, Serial Storage Architecture (SSA) and Fibre Channel-Arbitrated Loop (FC-AL) are considered as the next generation storage interfaces with broad industry support. Both technologies support simple cabling, long transmission distance, high data bandwidth, large capacity, fault tolerance, and fair sharing of link bandwidth. In this paper, a tutorial and a comparison of these two technologies are presented. The tutorial examines their interface specifications, transport protocols, fairness algorithms, and capabilities of fault tolerance. The comparison focuses on their protocol overhead, flow control, fairness algorithms, and fault tolerance. The paper also summarizes the recently proposed Aaron Proposal which incorporates features from both SSA and FC-AL and targets at merging these two technologies.

Interface comparisons: SSA versus FC-AL

The serial storage architecture and fibre channel-arbitrated loop interfaces offer a simple cabling system, higher bandwidth, the ability to connect more than 100 disks, fault tolerance, and fair accesses on the channel. This article investigates the performance of these two emerging serial storage interfaces for fairness, latency, overhead and aggregate throughput under various traffic loads.

Supporting continuous media: is Serial Storage Architecture (SSA) better than SCSI?

The existing SCSI (Small Computer System Interface) parallel bus has been widely used in supporting multimedia applications. However, it may not fully utilize the aggregate throughput from disks in supporting continuous media because of its unfair bus accesses. The emerging serial interface, Serial Storage Architecture (SSA), provides high data bandwidth, fair accesses and fault tolerance. The fairness algorithm in SSA ensures that a fraction of the data bandwidth is allocated to each disk. In this paper, we study the performance of SSA and SCSI in supporting continuous media.

On providing highly available fault-tolerant video-on-demand services

Due to the large number of magnetic disks involved in a video server, the probability of disk failure is fairly high. Traditional parity-based and duplex-based (mirroring) approaches provide full data recovery, but do not guarantee full availability of the service in the presence of even a single disk failure. If a video server would like to provide non-disruptible services to a large number of viewers, the issue of high availability needs to be addressed. The authors proposed a general scheme for accomplishing both fault tolerance and high availability in a video server. The tradeoffs between memory buffer space and redundant disk storage space are discussed. A video allocation problem based on the proposed scheme is formulated and heuristic algorithms to solve this problem are presented. The scheme can be easily implemented in a highly available fault-tolerant video server.

Performance of a Scalable Multimedia Server with Shared-Storage Clusters

The existing SCSI parallel bus has been widely used in various multimedia applications. However, due to the unfair bus accesses the SCSI bus may not be able to fully utilize the potential aggregate throughput of disks. The number of disks that can be attached to the SCSI bus is limited, and link level fault tolerance is not provided. The serial storage interfaces such as Serial Storage Architecture (SSA) provide high data bandwidth, fair accesses, long transmission distance between adjacent devices (disks or hosts) and link level fault tolerance. The fairness algorithm of SSA ensures a fraction of data bandwidth to be allocated to each device. In this paper we would like to know whether SSA is a better alternative in supporting continuous media than SCSI. The scalability of a multimedia server is very important since the storage requirement may grow incrementally as more contents are created and stored. SSA in a shared-storage cluster environment also supports concurrent accesses by different hosts as long as their access paths are not overlapped. This feature is called spatial reuse. Therefore, the effective bandwidth over an SSA can be higher than the raw data bandwidth and the spatial reuse feature is critical to the scalability of a multimedia server. This feature is also included in FC-AL3 with a new mode called Multiple Circuit Mode (MCM). Using MCM, all devices can transfer data simultaneously without collision. In this paper we have investigated the scalability of shared-stroage clusters over an SSA environment.