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1.
Floor control for multimedia conferencing and collaboration 总被引:12,自引:0,他引:12
Floor control allows users of networked multimedia applications to utilize and share resources such as remote devices, distributed
data sets, telepointers, or continuous media such as video and audio without access conflicts. Floors are temporary permissions
granted dynamically to collaborating users in order to mitigate race conditions and guarantee mutually exclusive resource
usage. A general framework for floor control is presented. Collaborative environments are characterized and the requirements
for realization of floor control will be identified. The differences to session control, as well as concurrency control and
access control are elicited. Based upon a brief taxonomy of collaboration-relevant parameters, system design issues for floor
control are discussed. Floor control mechanisms are discerned from service policies and principal architectures of collaborative
systems are compared. The structure of control packets and an application programmer's interface are proposed and further
implementation aspects are elaborated. User-related aspects such as floor presentation, assignment, and the timely stages
of floor-controlled interaction in relation to user-interface design are also presented. 相似文献
2.
Handling a tertiary storage device, such as an optical disk library, in the framework of a disk-based stream service model,
requires a sophisticated streaming model for the server, and it should consider the device-specific performance characteristics
of tertiary storage. This paper discusses the design and implementation of a video server which uses tertiary storage as a
source of media archiving. We have carefully designed the streaming mechanism for a server whose key functionalities include
stream scheduling, disk caching and admission control. The stream scheduling model incorporates the tertiary media staging
into a disk-based scheduling process, and also enhances the utilization of tertiary device bandwidth. The disk caching mechanism
manages the limited capacity of the hard disk efficiently to guarantee the availability of media segments on the hard disk.
The admission controller provides an adequate mechanism which decides upon the admission of a new request based on the current
resource availability of the server. The proposed system has been implemented on a general-purpose operating system and it
is fully operational. The design principles of the server are validated with real experiments, and the performance characteristics
are analyzed. The results guide us on how servers with tertiary storage should be deployed effectively in a real environment.
RID="*"
ID="*" e-mail: hjcha@cs.yonsei.ac.kr 相似文献
3.
Wen-Syan Li K.Selçuk Candan Kyoji Hirata Yoshinori Hara 《The VLDB Journal The International Journal on Very Large Data Bases》2001,9(4):312-326
Due to the fuzziness of query specification and media matching, multimedia retrieval is conducted by way of exploration.
It is essential to provide feedback so that users can visualize query reformulation alternatives and database content distribution.
Since media matching is an expensive task, another issue is how to efficiently support exploration so that the system is not
overloaded by perpetual query reformulation. In this paper, we present a uniform framework to represent statistical information
of both semantics and visual metadata for images in the databases. We propose the concept of query verification, which evaluates queries using statistics, and provides users with feedback, including the strictness and reformulation alternatives
of each query condition as well as estimated numbers of matches. With query verification, the system increases the efficiency
of the multimedia database exploration for both users and the system. Such statistical information is also utilized to support
progressive query processing and query relaxation.
Received: 9 June 1998/ Accepted: 21 July 2000 Published online: 4 May 2001 相似文献
4.
Steve Benford John Bowers Lennart E. Fahlén Chris Greenhalgh Dave Snowdon 《Multimedia Systems》1997,5(2):93-104
This paper explores the issue of user embodiment within collaborative virtual environments. By user embodiment we mean the
provision of users with appropriate body images so as to represent them to others and also to themselves. By collaborative
virtual environments we mean multi-user virtual reality systems which explicitly support cooperative work (although we argue
that the results of our exploration may also be applied to other kinds of collaborative system). The main part of the paper
identifies a list of embodiment design issues grouped by the general themes of personal representation, conveying activity,
embodiment in heterogeneous systems, embodiment of agents, and ethical issues. These issues are illustrated with examples
from our own DIVE and MASSIVE collaborative virtual environments. The paper also uses this set of issues as an analytical
framework for comparing a number of other communication technologies. 相似文献
5.
A. Savidis N. Maou I. Pachoulakis C. Stephanidis 《Universal Access in the Information Society》2002,1(4):274-287
The concept of ubiquitous computing reflects an infrastructure in which users are engaged in mobile interaction sessions within
environments composed of dynamically varying computational resources. In this paradigm, applications are required to continuously
follow end users and provide high-quality interaction while migrating among different computing devices and dynamically utilizing
the available input/output (I/O) resources of each device. In the context of such interaction scenarios, the principle of
continuity, which emphasizes the uninterrupted sequence of dialogue activities, is put forward as a key design goal. This
paper presents an application experiment demonstrating interface migration, distributed I/O control, and dynamic I/O reconfiguration.
The adopted dialogue design approach is discussed, along with the identified interaction design requirements, from the perspective
of dialogue continuity. Finally, the employed software engineering strategy is presented, elaborating on the way dialogue
mobility, distribution, and dynamic I/O control have been accomplished.
Published online: 11 June 2002 相似文献
6.
为了解决流媒体直播在Internet中传输带宽不足、用户接入多样性等问题,本文探讨了流媒体在IP网络中一般的传输控制技术,提出了一种基于联播的流媒体实时传输控制策略以适应网络带宽的动态变化。首先通过组播方式以及RTP/RTCP协议实现流媒体的实时传输;之后对自适应传输的算法进行了详细的分析和设计,并采用多线程技术实现了网络状况监测和实时码流切换控制;最后通过研究及实验数据分析对比,证明该方案可提高多路并发流传输效率的有效性,并且可以给客户端用户带来较好的用户体验。 相似文献
7.
Giancarlo Fortino Carlo Mastroianni Wilma Russo 《Journal of Network and Computer Applications》2009,32(1):135-157
Content distribution networks have recently been introduced as a more efficient alternative to centralized servers for the delivery of static content as well as media streaming services ranging from TV broadcasts to video on-demand. Content Distribution Networks can also efficiently provide collaborative playback service, which allows a synchronous group of users to select, simultaneously watch altogether and share the control of a multimedia session. This paper presents the definition and analysis of the Hierarchical Cooperative Control Protocol (HCOCOP), which allows a synchronous group of users to share the control of the media streaming session provided by a Content Distribution Network. The analysis phase, which was supported by discrete-event simulation, was carried out to characterize the efficiency of the protocol on the basis of the following defined performance indices: blocking probability, denial probability, server load and network load. The performances obtained for architectures based on Content Distribution Networks are compared with those obtained for centralized architectures providing collaborative playbacks. The comparison shows that HCOCOP significantly improves performance of media streaming control. 相似文献
8.
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. 相似文献
9.
Many video applications tolerate continuous media (CM) scaling. Scaling is acceptable due to human tolerance to degradation
in picture quality, frame loss, and end-to-end delay. CM scaling enables the network to utilize its resources efficiently
for supporting additional customers and to increase its revenue. However, due to quality degradation, users will not be willing
to tolerate scaling unless it is coupled with monetary or availability incentives. We propose a pricing policy and a corresponding
admission control scheme for scalable video applications. The pricing policy is two-tiered, based on a connection set-up component
and a scalable component. Connections that are more scalable are charged less, but are more liable to be degraded. The proposed
policy trades off performance degradation with monetary incentives to improve user benefit and network revenue and to decrease
the blocking probability of connection requests. We demonstrate by means of simulation that this policy encourages users to
specify the scalability of an application to the network. 相似文献
10.
The idea of the information society is pervasive and varied and, in this context, universal access is itself a multi-faceted
concept. However, the notion of universality presupposes an analysis and understanding of what both unifies and discriminates
among different individual members of a community of technology users. This paper addresses these ideas and, in particular,
seeks to illustrate some techniques which can support such an analysis in a variety of task domains. Of special interest here
is a specific case study which examines the use of biometric processing as a means of managing access in the broadest sense.
It is argued that not only is the field of biometric measurement one where understanding similarities and differences is the
essence of what is required, but also that this offers the opportunity to establish and explore a variety of practical techniques
of very wide significance in the context of universal access.
Published online: 18 May 2001 相似文献
11.
The elicitation or communication of user requirements comprises an early and critical but highly error-prone stage in system
development. Socially oriented methodologies provide more support for user involvement in design than the rigidity of more
traditional methods, facilitating the degree of user–designer communication and the ‘capture’ of requirements. A more emergent
and collaborative view of requirements elicitation and communication is required to encompass the user, contextual and organisational
factors. From this accompanying literature in communication issues in requirements elicitation, a four-dimensional framework
is outlined and used to appraise comparatively four different methodologies seeking to promote a closer working relationship
between users and designers. The facilitation of communication between users and designers is subject to discussion of the
ways in which communicative activities can be ‘optimised’ for successful requirements gathering, by making recommendations
based on the four dimensions to provide fruitful considerations for system designers. 相似文献
12.
A buffer-inventory-based dynamic scheduling algorithm for multimedia-on-demand servers 总被引:2,自引:0,他引:2
We present a producer-consumer model of multimedia-on-demand (MOD) servers. The producer retrieves media data from a disk
and places it into a set of buffers, while the consumer sends out the data in the buffers to the users. We develop for the
producer a buffer-inventory-based dynamic scheduling (BIDS) algorithm that guarantees non-zero inventory and non-overflow
of data in the buffers to meet the continuity requirement and no-loss of data for each media stream. The algorithm can deal
with heterogeneous me dia streams as well as the transient circumstances upon service completions and arrivals of new requests.
To smooth out the impact of bursty data of variable-bit-rate media streams and therefore increase the maximum admissible load
of requests, we also introduce into the scheduling scheme a time-scale-dependent peak consumption rate and a virtual cycle
time. Based on BIDS, an effective admission control mechanism can be easily established by checking two simple conditions
respectively on the overall system load and buffer size. Our algorithm is very easy to implement. Experiments carried out
with an actual disk system and real video stream data verify that it is more robust compared to static scheduling algorithms
previously proposed in the literature, especially when handling variable-bit-rate media streams. 相似文献
13.
S. Arbanowski S. van der Meer S. Steglich R. Popescu-Zeletin 《Personal and Ubiquitous Computing》2001,5(1):34-37
In the last few years, a variety of concepts for service integration and corresponding systems have been developed. On the
one hand, they aim for the interworking and integration of classical telecommunications and data communications services.
On the other, they are focusing on universal service access from a variety of end-user systems. Many of the technical problems,
resulting from the service integration, and service personalisation have been solved during the last years. However, all these
systems are driven by the concept of providing several technologies to users by keeping the peculiarity of each service.
Looking at humans’ communication behaviour and their communication space, it is obvious that human beings interact habitually
in a set of contexts with their environment. The individual information preferences and needs, persons to interact with, and
the set of devices controlled by each individual define their personal communication space. Following this view, a new approach
is to build communication systems not on the basis of specific technologies, but on the analysis of the individual communication
spaces. The result is a communication system adapted to the demands of each individual (I-centric). The communication system
will act on behalf of users’ demands, reflecting recent actions to enable profiling and self-adaptation to contexts and situations.
In this paper, we introduce I-centric Communications, an approach to design communication systems that adapt themselves to
the individual communication space and individual environment and situation. In this context “I” means I, or individual, “Centric”
means adaptable to I requirements and a certain user environment. 相似文献
14.
Eve M. Schooler 《Multimedia Systems》1996,4(5):210-225
As integrated services have become available to the desktop, users have embraced new modes of interaction, such as multimedia
conferencing and collaborative computing. In this paper, we provide a survey of past and present research that has influenced
this application area, and describe research directions for the future. 相似文献
15.
Gerd Schürmann 《Multimedia Systems》1996,4(5):281-295
Electronic mail for traditional text exchange as asynchronous communication means between computer users is widely built upon
in many application areas. Whereas Multimedia-Mail systems – including text, graphics, still images, audio, video and documents
– were limited to isolated communities – at least two very promising approaches are being under development: the MIME (Multipurpose
Internet Mail Extension), an extension of Internet Mail as well as the Multimedia Teleservice based on CCITT Recommendation
X.400(88) being under development within the BERKOM project funded by the German TELEKOM. The store-and-forward mechanism
inherent to electronic mail is complemented in the later one by an additional exchange mechanism allowing the resolution of
references to message content, e.g. video. Such references may be put into a message in place of the content itself. Internet/MIME
and OSI/X.400, their interworking, asynchronous information server access via Multimedia-Mail, as well as possible future
developments especially in the area of asynchronous Computer Supported Cooperative Work (CSCW) are discussed. 相似文献
16.
Securing SOAP e-services 总被引:4,自引:0,他引:4
E. Damiani S. De Capitani di Vimercati S. Paraboschi P. Samarati 《International Journal of Information Security》2002,1(2):100-115
Remote service invocation via HTTP and XML promises to become an important component of the Internet infrastructure. Work
is ongoing in the W3C XML Protocol Working Group to define a common standard, and solutions like SOAP and XML-RPC are already
used in a few situations, demonstrating the potential. However, no standard technique for access control security is currently
defined for these protocols. In this paper, we propose an approach that relies on the XML structure of SOAP requests to support
fine-grained authorizations at the level of individual XML elements and attributes that comprise a SOAP call. The result is
a simple yet general technique to specify and enforce fine-grained access control for e-services.
Published online: 13 November 2001 相似文献
17.
Video and audio compression techniques allow continuous media streams to be transmitted at bit rates that are a function
of the delivered quality of service. Digital networks will be increasingly used for the transmission of such continuous media
streams. This paper describes an admission control policy in which the quality of service is negotiated at stream initiation,
and is a function of both the desired quality of service and the available bandwidth resources. The advantage of this approach
is the ability to robustly service large numbers of users, while providing increased quality of service during low usage periods.
Several simple algorithms for implementing this policy are described and evaluated via simulation for a video-on-demand scenario. 相似文献
18.
Domenico Ferrari 《Multimedia Systems》1996,4(6):299-304
Protocols for multimedia communication are needed to integrate into a single network services intended to satisfy the different
requirements of multiple types of traffic. An essential prerequisite for designing these protocols is that the services to
be offered by the network must be selected and specified in detail. We present the service models proposed, or being developed,
by the Internet community, by the ATM community, and by the Tenet Group. We compare their common characteristics, which reveal
the characteristics of the first integrated services networks are likely to offer. The services referred to in this paper
are those at the network and transport layers, which support the services to be offered to the system's end users. 相似文献
19.
This paper presents an overview of some of the key issues which have emerged in recent years surrounding the growth and application
of e-commerce in the global information infrastructure (GII). Increased access to the Internet, the Internet as a strategic
resource for business, trust and security issues surrounding e-commerce, and calls for a regulatory and legal framework to
protect buyers and sellers, are four critical areas that need to be addressed by industry, government and the individual.
In attempting to synthesise some of the contemporary key issues in e-commerce, we conclude by suggesting that research into
this subject must embrace both external and internal factors as this will engender a deeper understanding of the role of e-commerce
in the so-called ‘knowledge-driven economy’. 相似文献
20.
This study deals with cognitive cooperation in the context of the design of cooperative computer support for sharing aircraft
conflict detection and resolution tasks between human and machine in air traffic control. In order to specify some necessary
cooperative capabilities of such a system, we have observed an artificial situation on a simulator where two radar controllers
(RCs) had to cooperate for the management of a heavy traffic within a single sector. This paper reports the analysis of the
verbal communications between the two RCs recorded during the simulation. The results enabled us to describe the elements
of a common frame of reference (COFOR), elaborated and updated by the two RCs, as a crucial cooperative activity in this kind
of situation. They also show the role of this COFOR in the implicit detection and resolution of interference between the RCs’
individual activities. Their contribution to design, associated with other investigations and the state of the art, is discussed. 相似文献