The multimedia multicasting problem

This paper explores the problems associated with the multicasting of continuous media to support multimedia group applications. The interaction between multicasting and the delivery of multiple time-correlated continuous-media streams with real-time delay requirements poses various new and interesting problems in research on communication protocols and architectures. We describe these problems, and identify where the opportunities are for effective solutions, all in the context of providing an overview of the current state of research in multimedia multicasting. The issues we discuss include quality of service, resource reservations, routing, error and traffic control, heterogeneity, and the use of hierarchical coding and open-loop control techniques.     

Scalability support for multiparty multimedia communications

In this paper, we propose a new communication abstraction known as the group channel which facilitates and supports the implementation of multiparty interactive multimedia (MIM) applications such as video conferencing. The group channel is a high-level abstraction for group communication. The credit scheme and the dynamic bandwidth calibration scheme are provided as an integral part of the group channel service for allocating network bandwidth dynamically as participants join and leave the group channel. The multimedia transport protocol (MTP) is proposed as a realization of the group channel service in the ATM network. Its prototype implementation and a simple multiparty video-conferencing application built on top of the MTP prototype are described in this paper. Our results show that the group channel is capable of guaranteeing the performance of MIM applications irrespective of the group size and differences in workstation speeds.     

Design and evaluation of a multimedia storage server for mixed traffic

The relative simplicity of access to digital communications nowadays and the simultaneous increase in the available bandwidth are leading to the definition of new telematic services, mainly oriented towards multimedia applications and interactivity with the user. In the near future, a decisive role will be played in this scenario by the providers of interactive multimedia services of the on-demand type, which will guarantee the end user a high degree of flexibility, speed and efficiency. In this paper, some of the technical aspects regarding these service providers are dealt with, paying particular attention to the problems of storing information and managing service requests. More specifically, the paper presents and evaluates a new storage technique based on the use of disk array technology, which can manage both typical multimedia connections and traditional requests. The proposed architecture is based on the joint use of the partial dynamic declustering and the information dispersal algorithm, which are employed for the allocation and retrieval of the data stored on the disk array. We also define efficient strategies for request management in such a way as to meet the time constraints imposed by multimedia sessions and guarantee good response times for the rest of the traffic. The system proposed is then analyzed using a simulation approach.     

Dynamic real-time scheduling strategies for interactive continuous media servers

In this paper, we propose and study a dynamic approach to schedule real-time requests in a video-on-demand (VOD) server. Providing quality of service in such servers requires uninterrupted and on-time retrieval of motion video data. VOD services and multimedia applications further require access to the storage devices to be shared among multiple concurrent streams. Most of the previous VOD scheduling approaches use limited run-time,0 information and thus cannot exploit the potential capacity of the system fully. Our approach improves throughput by making use of run-time information to relax admission control. It maintains excellent quality of service under varying playout rates by observing deadlines and by reallocating resources to guarantee continuous service. It also reduces start-up latency by beginning service as soon as it is detected that deadlines of all real-time requests will be met. We establish safe conditions for greedy admission, dynamic control of disk read sizes, fast initial service, and sporadic services. We conduct thorough simulations over a wide range of buffer capacities, load settings, and over varying playout rates to demonstrate the significant improvements in quality of service, throughput and start-up latency of our approach relative to a static approach.     

Failure recovery algorithms for multimedia servers

In this paper, we present two novel disk failure recovery methods that utilize the inherent characteristics of video streams for efficient recovery. Whereas the first method exploits the inherent redundancy in video streams (rather than error-correcting codes) to approximately reconstruct data stored on failed disks, the second method exploits the sequentiality of video playback to reduce the overhead of online failure recovery in conventional RAID arrays. For the former approach, we present loss-resilient versions of JPEG and MPEG compression algorithms. We present an inherently redundant array of disks (IRAD) architecture that combines these loss-resilient compression algorithms with techniques for efficient placement of video streams on disk arrays to ensure that on-the-fly recovery does not impose any additional load on the array. Together, they enhance the scalability of multimedia servers by (1) integrating the recovery process with the decompression of video streams, and thereby distributing the reconstruction process across the clients; and (2) supporting graceful degradation in the quality of recovered images with increase in the number of disk failures. We present analytical and experimental results to show that both schemes significantly reduce the failure recovery overhead in a multimedia server.     

Synchronized delivery and playout of distributed stored multimedia streams

Multimedia streams such as audio and video impose tight temporal constraints for their presentation. Often, related multimedia streams, such as audio and video, must be presented in a synchronized way. We introduce a novel scheme to ensure the continuous and synchronous delivery of distributed stored multimedia streams across a communications network. We propose a new protocol for synchronized playback and compute the buffer required to achieve both, the continuity within a single substream and the synchronization between related substreams. The scheme is very general and does not require synchronized clocks. Using a resynchronization protocol based on buffer level control, the scheme is able to cope with server drop-outs and clock drift. The synchronization scheme has been implemented and the paper concludes with our experimental results.     

On periodic resource scheduling for continuous-media databases

The Enhanced Pay-Per-View (EPPV) model for providing continuous-media services associates with each continuous-media clip a display frequency that depends on the clip's popularity. The aim is to increase the number of clients that can be serviced concurrently beyond the capacity limitations of available resources, while guaranteeing a constraint on the response time. This is achieved by sharing periodic continuous-media streams among multiple clients. The EPPV model offers a number of advantages over other data-sharing schemes (e.g., batching), which make it more attractive to large-scale service providers. In this paper, we provide a comprehensive study of the resource-scheduling problems associated with supporting EPPV for continuous-media clips with (possibly) different display rates, frequencies, and lengths. Our main objective is to maximize the amount of disk bandwidth that is effectively scheduled under the given data layout and storage constraints. Our formulation gives rise to -hard combinatorial optimization problems that fall within the realm of hard real-time scheduling theory. Given the intractability of the problems, we propose novel heuristic solutions with polynomial-time complexity. We also present preliminary experimental results for the average case behavior of the proposed scheduling schemes and examine how they compare to each other under different workloads. A major contribution of our work is the introduction of a robust scheduling framework that, we believe, can provide solutions for a variety of realistic EPPV resource-scheduling scenarios, as well as any scheduling problem involving regular, periodic use of a shared resource. Based on this framework, we propose various interesting research directions for extending the results presented in this paper. Received June 9, 1998 / Accepted October 13, 1998     

Spatio-temporal effects of multimedia objects storage and delivery for video-on-demand systems

As the number of video streams to be supported by a digital video delivery system (DVDS) increases, an improved understanding of the necessity for reliable and cost-efficient support for a considerable number of video streams (in the magnitude of tens of thousands), and the dependency largely on software capabilities emerges. Even in the presence of an optimal hardware configuration, or model, and associated costs, using software to exploit the underlying hardware capabilities is of paramount importance. Although a number of DVDSs have become operational, their ability to deliver the required services mainly depends on the small number of streams supported and the hardware trade-offs. It is imperative that current software developments account for the eventual scalability of the number of video streams without commensurate increase in hardware. In this paper, we present strategies for the management of video streams in order to maintain and satisfy their space and time requirements. We use a DVDS architectural model with functionally dichotomized nodes: a single-node partition is responsible for data retrieval, while the remaining partition of nodes accepts user requests, determines object locations, and routes requests through the network that connects both partitions. We present a detailed analysis of the issues related to queuing I/O requests and data buffering. The discussion includes the requirements for arranging and scheduling I/O requests and data buffers, with the objective of guaranteeing the required data availability rates for continuous media display.     

Infopipes: An abstraction for multimedia streaming

To simplify the task of building distributed streaming applications, we propose a new abstraction for information flow – Infopipes. Infopipes make information flow primary, not an auxiliary mechanism that is hidden away. Systems are built by connecting predefined component Infopipes such as sources, sinks, buffers, filters, broadcasting pipes, and multiplexing pipes. The goal of Infopipes is not to hide communication, like an RPC system, but to reify it: to represent communication explicitly as objects that the program can interrogate and manipulate. Moreover, these objects represent communication in application-level terms, not in terms of network or process implementation.     

MING-I: a distributed interactive multimedia document development mechanism

The next generation of interactive multimedia documents can contain both static media, e.g., text, graph, image, and continuous media, e.g., audio and video, and can provide user interactions in distributed environments. However, the temporal information of multimedia documents cannot be described using traditional document structures, e.g., Open Document Architecture (ODA) and Standard Generalized Mark-up Language (SGML); the continuous transmission of media units also raises some new synchronization problems, which have not been met before, for processing user interactions. Thus, developing a distributed interactive multimedia document system should resolve the issues of document model, presentation control architecture, and control scheme. In this paper, we (i) propose a new multimedia document model that contains the logical structure, the layout structure, and the temporal structure to formally describe multimedia documents, and (ii) point out main interaction-based synchronization problems, and propose a control architecture and a token-based control scheme to solve these interaction-based synchronization problems. Based on the proposed document model, control architecture, and control scheme, a distributed interactive multimedia document development mechanism, which is called MING-I, is developed on SUN workstations.     

Scheduling and data layout policies for a near-line multimedia storage architecture

Recent advances in computer technologies have made it feasible to provide multimedia services, such as news distribution and entertainment, via high-bandwidth networks. The storage and retrieval of large multimedia objects (e.g., video) becomes a major design issue of the multimedia information system. While most other works on multimedia storage servers assume an on-line disk storage system, we consider a two-tier storage architecture with a robotic tape library as the vast near-line storage and an on-line disk system as the front-line storage. Magnetic tapes are cheaper, more robust, and have a larger capacity; hence, they are more cost effective for large scale storage systems (e.g., video-on-demand (VOD) systems may store tens of thousands of videos). We study in detail the design issues of the tape subsystem and propose some novel tape-scheduling algorithms which give faster response and require less disk buffer space. We also study the disk-striping policy and the data layout on the tape cartridge in order to fully utilize the throughput of the robotic tape system and to minimize the on-line disk storage space.     

A standard model for multimedia synchronization: PREMO synchronization objects

This paper describes an event-based synchronization mechanism, which is at the core of the inter-media synchronization in the upcoming standard for multimedia presentation, PREMO. The synchronization mechanism of PREMO is a powerful tool, based on a small number of concepts, and on cooperation among active objects, and represents a synthesis of various synchronization models described in the literature. This model can serve as a basis for the implementation of complex synchronization patterns in multimedia presentations, both purely event-based, as well as time-based.     

A multimedia social interaction service for inclusive community living: Initial user trials

The move from institution to community care has resulted in many people receiving care at home. For some, disability or frailty restricts their involvement in social activities outside the home, resulting in unacceptable social isolation. This problem is compounded if the person has a speech or language impairment. In this paper, we will describe a communication service designed to provide nonspeaking people with a means to interact socially when living independently, based on the sharing of stories using pictures and other media. Initial exploration on the usability of the system by a pair of representative users will be described. Published online: 6 November 2002     

Broadband Cellular Radio Telecommunication Technologies in Distance Learning: A Human Factors Field Study

This paper presents a virtual classroom field experiment utilising broadband cellular radio telecommunication technologies and involving real users. The aim of the investigation was to experiment in the field cellular broadband systems in realising virtual classroom situations. In particular, we investigated learners’ performance and usability aspects of the multimedia tele-education system including ease of use, usefulness, telepresence and users’ satisfaction about the system. Results confirmed the effectiveness of the multimedia system in terms of both technical and psychological features. Some operational results and practical solutions were obtained as well. They included the basic features of multimedia systems used in virtual classroom and the correct procedures for training teachers and learners in the equipment use.     

RCSP and stop-and-go: a comparison of two non-work-conserving disciplines for supporting multimedia communication

To support emerging real-time applications, high-speed integrated services networks must provide end-to-end performance guarantees on a per-connection basis in a networking environment. Resource management algorithms must accommodate traffic that may get burstier as it traverses the network due to complex interactions among packet streams at each switch. To address this problem, several non-work-conserving packet-service disciplines have been proposed. Non-work-conserving servers may be idle and hold packets under certain conditions, to reconstruct, fully or partially, the traffic pattern of the original source inside the network and prevent the traffic from becoming burstier. We compare two non-work-conserving service disciplines. Stop-and-go uses a multilevel framing strategy to allocate resources in a single switch and to ensure traffic smoothness throughout the network. Rate controlled static priority (RCSP) decouples the server functions with two components: (1) a regulator to control traffic distortion introduced by multiplexing effects and load fluctuations in previous servers, and 2) a static priority scheduler to multiplex the regulated traffic. We compare the two service disciplines in terms of traffic specification, scheduling mechanism, buffer space requirement, end-to-end delay characteristics, connection admission-control algorithms, and achievable network utilization. The comparison is first done analytically, and then empirically by using two 10-min traces of MPEG compressed video.     

2PSM: an efficient framework for searching video information in a limited-bandwidth environment

We present a novel technique, called 2-Phase Service Model, for streaming videos to home users in a limited-bandwidth environment. This scheme first delivers some number of non-adjacent data fragments to the client in Phase 1. The missing fragments are then transmitted in Phase 2 as the client is playing back the video. This approach offers many benefits. The isochronous bandwidth required for Phase 2 can be controlled within the capability of the transport medium. The data fragments received during Phase 1 can be used to provide an excellent preview of the video. They can also be used to facilitate VCR-style operations such as fast-forward and fast-reverse. Systems designed based on this method are less expensive because the fast-forward and fast-reverse versions of the video files are no longer needed. Eliminating these files also improves system performance because mapping between the regular files and their fast-forward and fast-reverse versions is no longer part of the VCR operations. Furthermore, since each client machine handles its own VCR-style interaction, this technique is very scalable. We provide simulation results to show that 2-Phase Service Model is able to handle VCR functions efficiently. We also implement a video player called {\em FRVplayer}. With this prototype, we are able to judge that the visual quality of the previews and VCR-style operations is excellent. These features are essential to many important applications. We discuss the application of FRVplayer in the design of a video management system, called VideoCenter. This system is intended for Internet applications such as digital video libraries.     

The optimal location of replicas in a network using a READ-ONE-WRITE-ALL policy

We consider the problem of locating replicas in a network to minimize communications costs. Under the assumption that the read-one-write-all policy is used to ensure data consistency, an optimization problem is formulated in which the cost function estimates the total communications costs. The paper concentrates on the study of the optimal communications cost as a function of the ratio between the frequency of the read and write operations. The problem is reformulated as a zero-one linear programming problem, and its connection to the p-median problem is explained. The general problem is proved to be NP-complete. For path graphs a dynamic programming algorithm for the problem is presented. Received: May 1993 / Accepted: June 2001