Introduces the design, implementation and evaluation of a generic software architecture for on-demand video servers. We describe different key components for controlling the storage and network devices within the server. The interactive collaborations between these software components are also illustrated. The experimental results indicate a very promising direction in exploring the right combinations of these software components. The server is thus able to increase the number of concurrent video accesses with the same hardware configuration. For instance, with the right combinations, the system achieved about 80% of the storage system bandwidth of four disks, about 70% of the storage system bandwidth of six disks, and generally reached the maximal achieved SCSI bandwidth when eight disks are used over two SCSI buses. Our research and experimental results are based on video servers currently under construction across a variety of hardware platforms, including SMP, DMP and clusters of PCs or workstations. The most advanced prototype server is based on an SGI shared-memory multiprocessor with a mass storage system consisting of RAID-3 disk arrays. With all the enabling/management schemes, we were able to further investigate interesting research issues by considering the user's access profiles for taking advantage of popular video titles. The results were significant, with a range of 60% improvement given a 512 kByte block size. In addition to the experimental results, theoretical performance models were also developed that closely match to our collected experimental results.

Asynchronous transfer mode (ATM) networks are scalable via a wide variety of physical link speeds and can be run in both the local and wide areas. Bandwidth reservation and quality of service guarantees make ATM attractive to deliver multimedia information in real-time. Existing protocol suites can be extended. However, they do not give access to those characteristics. Therefore, applications demand an ATM application programming interface (API) to take advantage of those features. This paper covers a special syntax mapping of the ATM API services on top of X/Open Transport Interface (XTI) which is able to give applications access directly to the special quality and traffic services of an ATM network. A particular realization of the API on the XTI environment is proposed and implemented on the MacOS networking platform. It provides a flexible and modular design of the ATM networking. Finally, the paper concludes with one ATM-aware application (video on demand) which requires real-time streaming data.

Future video-on-demand (VOD) servers will need to support many existing and emerging video data types. These data types include 15-fps (frames per second) animation, 30-fps NTSC (National Television Systems Committee) quality video and 80-fps HDTV (High Definition Television) video. The different display speeds and frame sizes of these various video types impose a major constraint on the design of VOD storage systems. This paper presents the results of an experimental study, conducted on a Silicon Graphics Inc. Onyx computer system, that investigated the impact of these video types on the design of a VOD storage system. The key issues involved in supporting these different video types in a VOD environment are: (1) the video allocation method, and (2) the proper block size (a block is a basic unit of several contiguous video frames that will be accessed from several disks each time a request is made) to use for data striping and retrieval. Two allocation schemes, logical volume striping and application level striping, along with varying frame and block sizes for each of the three different video data types are examined. The focus of our study is to determine the maximum number of concurrent accesses that can be supported with a guaranteed quality of service. The degree of scalability (i.e., striping data over more disk arrays) of the experimental VOD system used is also studied.

Video-on-demand (VOD) systems can support multiple concurrent video accesses with guaranteed user-controlled quality of service (QoS). The growth of VOD systems is driven by the increasing need for distributed multimedia applications such as company training, distance learning, telemedicine, and home entertainment. We propose and demonstrate an ATM-based (asynchronous transfer mode) VOD system (including VOD servers, clients and connection networks) based on a Macintosh platform. ATM is a promising network standard which may satisfy various requirements of VOD systems. In this VOD system, time-based data are encoded and decoded using the MPEG (Moving Picture Experts Group) standard. Issues related to VOD system design, including the multimedia programming environment, the required system modification to support remote MPEG playback, ATM networking, process scheduling, and buffer management for both VOD servers and clients, are discussed and analyzed based on the Macintosh platform. A prototype VOD system is used to explore the design issues proposed. The Macintosh platform provided an efficient and jitter-free VOD system supporting MPEG movie playback through ATM networks.

Future video-on-demand (VoD) servers will need to support many existing and emerging video data types. These data types include 15-fps (frames per second) animation, 30-fps National Television Systems Committee (NTSC) quality video, and 60-fps high definition television (HDTV) video. The different display speeds and frame sizes of these various video types impose a major constraint on the design of VoD storage systems. This paper presents the results of an experimental study, conducted on a Silicon Graphics Inc. (SGI) Onyx computer system, that investigated the impact of these video types on the design of a VoD storage system. The key issues involved in supporting these different video types in a VoD environment are as follows: (1) the video allocation method and (2) the proper block size (a "block" is a basic unit of several contiguous video frames that will be accessed from several disks each time a request is made) to use for data striping and retrieval. Two allocation schemes, logical volume striping and application level striping, along with varying frame and block sizes for each of the three different video data types are examined. The focus of our study is to determine the maximum number of concurrent accesses that can be supported with a guaranteed quality-of-service (QoS). The degree of scalability (i.e., striping data over more disk arrays) of the experimental VoD system used is also studied. Based on our experimental results, application level striping demands smaller block sizes for all three video types, and more concurrent accesses can be distributed over the storage devices. The experimental results demonstrate that application level striping has excellent scalability for animation and NTSC videos.

Communication between processors has long been the bottleneck of distributed network computing. However, recent progress in switch-based high-speed local area networks (LANs) may be changing this situation. Asynchronous transfer mode (ATM) is one of the most widely-accepted and emerging high-speed network standards which can potentially satisfy the communication needs of distributed network computing. We investigate distributed network computing over local ATM networks. We first study the performance characteristics involving end-to-end communication in an environment that includes several types of workstations interconnected via a Fore Systems' ASX-100 ATM switch. We then compare the communication performance of four different application programming interfaces (APIs). The four APIs were Fore Systems' ATM API, the BSD socket programming interface, Sun's remote procedure call (RPC), and the parallel virtual machine (PVM) message passing library. Each API represents distributed programming at a different communication protocol layer. We evaluated two popular distributed applications, parallel matrix multiplication and parallel partial differential equations, over the local ATM network. The experimental results show that network computing is promising over local ATM networks, provided that the higher level protocols, device drivers, and network interfaces are improved.>

Recent progress in switch based high speed local area networks (LANs) makes distributed network computing promising. Three evolving switch based high speed networks are the High Performance Parallel Interface (HIPPI), Fiber Channel (FC), and Asynchronous Transfer Mode (ATM) standards. We study how high performance computing can be carried out over such networks. High performance computing can be characterized as follows: it includes multiple modules and each module is executed in a processor; its communication data flow forms a special application topology and usually such application topologies are regular; and it requires frequent communication between adjacent modules in the application topology. In order to reduce the amount of time required for a processor to set up a connection during the execution of an application, we propose a new communication protocol called the Virtual Permanent Connection (VPC). For a given application topology, a set of connections are set up and permanently maintained during the execution of the application. Communication between processors are via this group of connections. We study how a set of VPCs are chosen based on a given application topology (this process is called application topology embedding).

Emerging high-speed networks provide several hundred megabits per second to several gigabits per second of raw communication bandwidth. However, the maximum achievable throughput available to the end-user or application is quite limited. In order to fully utilize the network bandwidth and to improve the performance at the application level, a careful examination of I/O subsystems is essential. In this paper, we study one emerging high-speed network, the Fibre Channel network. The objectives of this study are: to understand how the I/O subsystem relates to network operations; to evaluate and analyze the performance of such a subsystem; and to propose possible approaches for improving the maximum achievable bandwidth. We show (by simply modifying device driver code) a 75% maximum achievable bandwidth improvement. Other ways of improving network performance are also discussed.>

Communication between processors has long been the bottleneck of distributed network computing. However recent progress in switch-based high-speed local area networks (LANs) may be changing the situation. Asynchronous transfer mode (ATM) is one of the most widely-accepted and emerging high-speed network standards which can potentially satisfy the communication needs of distributed network computing. We investigate distributed network computing over local ATM networks. We first study the performance characteristics involving end-to-end communication in an environment that includes several types of workstations interconnected via a Fore Systems' ASX-100 ATM Switch. We then compare the communication performance of four different application programming interfaces (APIs). The four APIs were Fore Systems ATM API, BSD socket programming interface, Sun's Remote Procedure Call (RPC), and the Parallel Virtual Machine (PVM) message passing library. Each API represents distributed programming at a different communication protocol layer. We evaluate parallel matrix multiplication over the local ATM network. The experimental results show that network computing is promising over local ATM networks.>