Distributed multimedia applications: A review

Review

Distributed multimedia applications: A review

Neil Williams and Gordon S Blair

The arrival of distributed multimedia technology has the potential both to create new application areas and augment those that already exist. However, to achieve this potential system developers must fully understand the nature of multimedia information systems and the mechanisms necessary for such systems to operate successfully. It is the quest for this knowledge which has initiated research into the needs of distributed multimedia applications. This paper provides a sdrvey of multimedia applications research, and assesses its contribution to the understanding of distributed multimedia applirations.

Key~vords: multimedia, distributed computing

Research advances in computer science often follow on from developments in underlying technology support�9 Distributed computh~g illustrates such an event with its emergence due to advances in processor, memory, and communications technologies. Technological advances have also led to the development of hardware support for multimedia computing. Until recently, the integration of these two types of system has been limited by the lack of suitable communications infrastructure. However, a progressive increase in network bandwidth now provides the ability to process multimedia information in a distributed system.

This new generation of information technology has the potential to both create new application areas and augment those that currently exist. However, to realize this potential it is important that application developers are provided with desired levels of system support. Distributed systems research must therefore understand the needs of applications and the mechanisms necessary for them to operate successfully. It is the quest for this understanding which has initiated research into the

Distributed Multimedia Research Group, Computing Department, Lancaster University, Bailrigg, Lancaster LAI 4YR, UK (Email: [nw,[email protected]) Paper received: 12 January 1992; revised paper received: 7 March 1992

needs of distributed multhnedia applications. This paper discusses this applications research with the following objectives:

�9 to provide a survey of research into distributed multimedia applications;

�9 to assess the contribution of applications research to the development of distributed multimedia computing.

T H E E M E R G E N C E O F M U L T I M E D I A

Trends in informat ion technology (a user perspective)

T o understand the motivation behind multimedia computing, it is important to consider information technology from the point of view of the end user (as opposed to the technologist). To an end user, information technology is concerned with access to various forms of information and the ability to cooperate through these forms of information. Any actual technology which helps in this task is merely a means to an end.

From this perspective, it is possible to identify two separate aspects of information technology, namely the forms o f media available to an end user and the ability to efficiently communicate using these media forms. In both these areas, the modern user of information is coming under increased pressure. These pressures are discussed in more details below.

Forms of media In recent years, there has been a dramatic increase in the range of media used to convey information. Initially, communication was limited to simple forms of media such as voice and paper. This century, however, has witnessed the introduction of a greater variety of media types such as the telephone and visual forms of media.

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Distributed multimedia applications: N Williams and G Blair

In the latter part of the century, this trend has accelerated and there is now a wide range of media types available to convey information.

These advances provide a great opportunity for new developments in a range of areas such as education and commerce. However, there are also a number of problems associated with the growth of information in society. In particular, there is a great danger of creating hzformation overload. This problem can be seen, for example, in business where executives are required to make decisions based on an ever increasing variety and volume of information. Similar problems are also occurring in areas such as government, health care and education.

Problems of communication A further trend in information technology from a user perspective is the decentralization of information. Most modern organizations are very large and tend to consist of a number or separate institutions spread across a wide geographical area. These institutions typically cooperate through the sharing and exchange of information. Thus, communication is a vital concern for most organizations and efficient communications can make the difference between successful operation and failure. Without the appropriate forms of communication, there is a danger of h~formation starvation, i.e. decision makers do not have the right information to make the correct decisions.

Requirements for information technology The end user is therefore faced with the two problems of information overload and information starvation. They may either have too much information or may not have the right information. There is therefore a need to help

�9 the end user to manage information to ease the burden created by the increasing importance of information. Essentially, the end user needs support to get the right information to the right people at the right time. This clearly cannot be achieved by manual systems. Thus, there is a requirement for automation in the process of information management.

Trends in informat ion technology (a systems perspective)

From a systems perspective, information technology is concerned with the processing of information and the ability to communicate information between different sites. More specifically, information technology is seen as a combination of computing technology and communications infrastructures. The aim of this technology is essentially to manage information for the end user.

The most noticeable trend in information technology from a system perspective has been the increasing hltegration of media. Traditionally, computer systems dealt exclusively with numerical calculations. However, text processing soon became an important concern for

computer designers. Communications technologies were also developed to Support the transmission o f textual and numerical data. More recently, there has been a dramatic increase in the range of media types supported by computers and communications technologies. Sig- nificant steps have been taken in integrating graphics into computer workstations and communications technology. Researchers are now tackling the harder problems presented by audio and video.

What is multimedia?

The previous sections have highlighted important trends in information technology from both the end user and technology perspective. Two themes have emerged from this discussion. Firstly, the variety of media types is an important feature of modern information systems. Secondly, in order to deal with the variety, httegration is a critical concern. These observations provide a good working definition o f multimedia:

MULTIMEDIA = VARIETY + INTEGRATION

It is necessary for a multimedia system to support a variety of media types. This could be as modest as text and graphics or as rich as anirfiation, audio and video. However, this alone is not sufficient for a multimedia environment. It is also important that the various sources of media types are integrated into a single system framework. A multflnedia system is then one which allows end users to share, communicate and process a variety of forms of information in an integrated manner.

In essence, multimedia systems are attempting to solve the problems of information management by integrating the various forms of media into the computer/communications infrastructure. There are two benefits of achieving this level of integration:

�9 the computer can help in the task of managing and processing the information;

�9 information users only have to deal with one integrated environment rather than a number of separate information subsystems.

This is tlae great benefit o f multimedia information systems and is the main motivation behind the current research on the subject.

Distributed multimedia computing

Multimedia systems have received a great deal of attention recently, and a number of successful prototypes have been developed. Some systems are also now available commercially. However, it is important to draw a distinction between multimedia systems which operate on a single computer workstation and those which can span a networked environment. Most of the

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developments to date have been on single workstations. There has been much less work on networked systems.

The term distributed multhnedia system is introduced to describe the general case of a number of workstations intercofinected by one or more networks. The problems of managing multimedia in a distributed system are great and introduce a number of unresolved research problems. In contrast, the technological problems of multimedia workstations are much better understood.

M U L T I M E D I A A P P L I C A T I O N S

The opportunities for multimedia computing are immense. There are many areas of application where the introduction of multimedia can enhance existing systems. Similarly, there are many new areas of application made possible by the emergence of multimedia. This section examines some'of the potential application areas of multimedia (with particular emphasis on distributed multimedia applications). Each of the following areas are covered:

�9 office automation; �9 service industry applications; �9 retail applications; e- domestic applications; �9 science and engineering; �9 cultural activities.

This section also highlights the emergence of computer supported co-operative work (CSCW) as an important development with implications for distributed multimedia technology.

Office applications

A main beneficiary of multimedia technology is envisaged as being office and business systems. Offices produce and consume large amounts of information which can take many forms. It is not surprising therefore that office systems have been widely targeted for pilot multimedia applications. The following sub-sections cover the various areas which have been identified for investigation by researchers.

Multimedia documents: creation, storage and retrieval Document production was one of the first application areas to be affected by the advent of multimedia computing. The integrated text/graphics word processor has been a commercial product for several years and has achieved widespread success through the popularity of desktop publishing. The extension of documents to incorporate audio and video is the obvious development path for this type of application. Research work in this area has tended to concentrate on two main issues, namely document editing and document storage and retrieval.


Document edithtg Document editors have been a popular research area in recent years due to their importance as a main component in a multimedia system. MINOS l'z, Dia- mond 3, HERODE 4 and BALZAC 5 have constructed editors which investigate the functionality required by end users of multimedia systems. These projects have mainly concentrated on the user interfaces of multimedia editors and their methods of viewing, editing and manipulating the various media types. They have also tended to be single user applications with little bearing on distributed systems research. It is, howev.er, apparent that multi-user editing is an application area which will become popular with increased usage of distributed multimedia computing 6. GUIDANCE 7 is currently attempting to produce design principles specific to multi-authored multimedia document preparation. Si- milarly, Multiwork 8 also investigated the cooperative working aspects of multimedia editing and group working in general.

hlformation browshlg Information browsing is a further application area which is important within a multimedia environment. However, the amount and variety of information within a multimedia system can be difficult to'browse through and may cause information overload. Hence, the methods of access to information and its presentation to the user are important issues to consider. The Thinking Machines Corporation 9, for example, is developing support for users to find and retrieve multimedia information from various platforms. Hyper- media I~ techniques are expected to be a useful aid to this form of information browsing and their potential is being investigated in HYTEA 11 and CAPS 12. DE- MON 13 is also developing support for interactive document presentation across a distributed system.

Storage and retrieval Multimedia documents present many problems" for storage and retrieval systems due to the range and bulk of the information 14. These problems have previously been addressed by MULTOS 15 and DOMESDAY 16 and similar research, is currently continuing i n SPRITE 17. The difficulties encountered when attempting to combat storage problems involve both computational and engineering issues. The computational view is concerned with the nature of documents, i.e. the information contained within them, the structure of that information, and its management. The engineering view in contrast is more directly related to overcoming the hardware limitations of storage technologies.

Computationally, multimedia documents are usually structured as compound objects consisting of a number of component parts, each part being a specific media type~8, 19. Storage of a document can then take place by parsing the document structure and sending the components to a device capable of recording that particular

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type of information. An example of this would be a text component being stored on a low capacity magnetic drive whilst a video component is written to a high speed optical device.

Retrieval of documents 2~ requires the various stored components to be accessed and brought to the requesting workstation. The methods used to facilitate this retrieval can be quite complex due to the nature of the information. Research is involved in using techniques such as query languages Is, knowledge based classifica- tion, and document modelling 2~ to support the retrieval process. The derivation of standards such as the Office Document Architecture (ODA) 22 is also a highly important objective for work inthis area. PODA-223, for example, is attempting to advance the ODA standard to support multimedia document handling in the context of multi-vendor systems.

The engineering difficulties of storage and retrieval arise from the.relatively low input/output bandwidth of storage devices ~md their limitations regarding multiple and conflicting access requests 24. It is expected that new storage technologies, perhaps similar to non-volatile memory modules, will be required before these problems can be satisfactorily solved 25. Additional issues include the need to synchronize the transmission of distributed document components as they are brought to a requesting workstation and the ability to tolerate failure situations within the communication system 26.

Requirements for multimedia office applications Investigations into the requirements of office environments have been numerous over the last few years due to the increase in computing support for tasks associated with office working. ASTRA 27, ELO 28, and PANDA 29 have attempted to understand office technol- ogY with an emphasis being placed on office integration and information exchange. The results of this research will be important in the development of multimedia systems within office environments. Current and future research into office system requirements will need to understand the potential for distributed multimedia computing and assess its expected benefits.

Multimedia electronic nmil Multimedia electronic mail is an application area which is likely to be applicable to a number of multimedia environments 3~ Unlike text mail, however, multimedia messages can be extremely large and difficult to manage 32. The size of mail messages, for example, may range from a few kilobytes to many megabytes 25 making the storage requirements extremely variable and difficult to foresee. It is possible that large components of mail messages such as video may be referenced, but not duplicated at receiving sites. Access to the message would re, quire real-time transmission of these components from the creator's location. Although this approach may help reduce storage problems, it involves a high degree of inter-system management. It

would be difficult for example, to allo W a mail application to safely delete a message component which was referenced by a number of receiving systems.

As well as being large, multimedia messages may also be highly structured (a mail message being an example of a multimedia document which consists of a number of different information components). Mail applications will have to understand the structure of messages sent from a range of different systems. Hence, the necessity for standards which describe how messages can be structured is an important issue in the development of multimedia mail applications. Until a full understanding of the structuring requirements of multimedia documents is achieved, however, it will be difficult to develop standards which are able to support tile full range of possibilities.

Service industry applications

The education, finance and health services have always been large consumers of computing technology. Many new developments in the computing industry have been initially derived from research in one of these three areas. It is not surprising, therefore, that all three are investigating the potential of multimedia for enhancing the services they provide.

Educational The use of multimedia in education has been widespread for many years. In schools and colleges within the UK there has been a continuous move towards computing support for teaching since the introduction of the home computer in the 1970s. This inexpensive technology has the capability to use text, image, and sound to supplement and enhance the more traditional teaching methods. It is interesting to note that unlike the commercial world where multimedia is considered a mechanism for processing types of information not previously available, multimedia in education has been utilized because of its ability to make learning an interesting and more desirable activity.

An additional breakthrough in educational multimedia came with the introduction of optical disk technology33.34. -The use of optical disks as information sources with interactive teaching applications has been highly useful in both schools and commercial training institutions 3s. With the initial lack of communications support, however, the full use of this type of application was constrained by the high cost of producing the information and the relatively low ability for its distribution. The emergence of the required communications technology is now allowing research to investigate the potential for teaching and training applications where central information sources can be accessed from remote sites. JANUS 36, LAT 37, and OLE 3s, for example, are currently assessing the benefits of distributed multimedia technology within the educational environment.


A number of pilot applications are also being developed within educational research to demonstrate the possibilities for distributed multimedia computing. Applications for creating multi-authored multimedia courseware are being developed within MATIC 39, AAT 4~ and CAPTIVE 41 whilst ESM BASE 42 is investigating the database requirements of authoring systems. Research within Livenet 43, EPOS 44, CAMCE 45 and OLEW 46 is more directly concerned with the access and distribution of information to course students. As educational systems become more automated and build up information libraries it will be likely that information will be exchanged between organizations on a regular basis. Standards for future educational systems, therefore, will become highly important with the increased level of organizational interworking. LEAST 47 is developing recommendations for emerging standards for the representation and exchange of information between educational systems.

Financial The finance industry is regarded as one of the world's main consumers of information. The success of a financial organization is dependent upon the effectiveness of its information gathering and communication systems. The nature of the financial markets requires that relevant information is quickly filtered out and made available to those people making investment decisions based on market conditions. The information received may be from a number of different sources, e.g. company reports and political statements, which may include a variety of media types. It is important, therefore, that the system receiving, communicating and presenting the information is capable of handling the various forms of information it may encounter. �9 To provide the necessary level of information proces-

sing and communications support requires the use of a distributed multimedia system. A number of financial application areas are, therefore, being studied to understand their information requirements. BANK'924s and MERCHANT 49 are two projects looking at the distribution aspects of banking and retail cash handling respectively. DIVIDEND 5~ and PROVIDE sl, meanwhile, are assessing the benefits of audio/visual communications within financial environments.

Health The health service consists of a wide range of equipment that produces high volumes of information in various forms. Scanning equipment, for example, produces video output whilst x-ray machines produce high quality images. The quality of the information available to medical staff and its accessibility are highly important when patients lives are at stake. To enhance this information or its access methods in any way is therefore an extremely useful endeavour.

Distributed multimedia computing provides the sup-


port infrastructure to build medical systems which can hold many forms of information and allow access to this information both quickly and easily from any location. Information systems with this level of processing and communications power will also benefit the administrative aspects of the health industry. Many of the current problems in the UK health service can be attributed to poor information systems which either do not provide enough information or do not allow information to flow properly throughout the organizational structure. Future information systems which support both multimedia and distribution will provide the platform needed to build the types of application required for medical environments.

A number of research projects have investigated the potential for multimedia in the health industry. Due to the importance of images in the medical field a number of projects including AEM152, COVIRA 53, FEIP 54, MURIM 55 and QUIRT 56 have all investigated image processing techniques to improve medical systems. Although not necessarily aimed at distributed multimedia technology these projects show the type of image processing performed in medical environments and highlight the importance of the image content. MU- SIC 57, MULTIMED 5s, AVICA 59 and the BERKOM Heart Hospital 6~ are more specifically aimed at the communication of information within a medical system. TELEMED 61 is also looking at the communication of medical data as well as its management and control within an information system. Further work in AIDMED 62, BIOLAB 63, HOME 64, MIM165, MEDI- C A 66 and MMONS 67 is developing support systems for medical staff who interact with multimedia information. Research in this area is also being undertaken at the University of Washington where they are developing a Digital Neuroanatomist Knowledge System 6s.

The research discussed above shows there is a great deal of activity in the medical field with respect to distributed multimedia technology. The objective of this research is to foresee the nature of future medical applications and the support infrastructures required to enable them. Standards are, of course, highly important if a number of health systems are to interwork successfully. Research in RICHE 69, Telemedicine v~ and SCP-ECG 7~, therefore, is attempting to develop standards for open systems to support health care.

Retail applications

Multimedia provides opportunities in many retail areas where the technology can be applied to provide customers with comprehensive, up to date information. The information provided may either describe a product or be the product itself and can be made available at a wide range of locations, including domestic properties. The potential of multimedia in the retail industry is being investigated in a number of areas.



Publishing Multimedia technology has the potential to affect the publishing industry in a variety of ways. Newspaper publishers, for example, have a similar need to finance organizations for quickly obtaining and communicating information from a number of sources. The availability of multimedia computing enhances the capabilities of the information systems which perform this task. DIMPE 72, for example, is investigating the support systems necessary for the publishing industry. Similar work is being carried out as part of the Telepublishing 73 project which is attempting to derive a future working scenario in the printing and publishing industry.

A further application area created by multimedia computing is electronic publications 74'75, i.e. the production of newspapers, magazines and books in electronic form enabling publishers to utilize audio and video in addition to text and image. On-line publications are able to provide readers with current information in a highly dynamic and interactive form. It is conceivable that electronic publications will eventually become an integral part of sophisticated information systems which can provide access to a variety of information available on a global multimedia network. This information including newspapers, books, journals, internal company reports, etc. would of course require a high degree of information management and widespread availability of high-speed networks. The BERKOM telepublishing

-system 6~ is investigating the use of high speed networking to support electronic publishing.

Travel and property The publishing industry has been mentioned as an area where multimedia technology can help replace paper based products with electronic alternatives. Electronic information has the advantage of being more comprehensive, up to date and interactive. The travel industry would also benefit from this advanced method of presenting information. Customers could be provided with access points to information systems with audio and video descriptions of holiday locations. If accessed via a hypermedia style interface, this capability would allow customers to browse at leisure through suitable holiday resorts and be presented with descriptions far superior to those currently provided in magazines. Many people travel to holiday resorts only to find they are disappointed with the eventual location. More informative information systems which provide custo- mer specific information through selective browsing would reduce this type of problem. The MCPR 76 project is looking at the issues related to the use of multimedia technology within the travel industry.

The property market is a further area where information is presented through paper-based media. Property is initially viewed through a magazine or newspaper which gives little indication of the location, condition and internal layout. A multimedia information system utilizing audio and video would provide a means of

showing potential customers much more detail than presently available. The extra information accessible through a computer system thus reduces the need for numerous visits to unsuitable properties. Distribution of the information would allow customers to view properties from anywhere in the country, from a local source, possibly even their own home. The benefits to both buyers, vendors, and property agents would be high due to the large reduction in time wasted over visiting numerous properties. GTE Laboratories 77 are currently assessing the use of distributed multimedia systems within the property market.

Domestic applications

For many years the main communication methods used to access domestic properties have been mail, telephone, radio and television. Each of these communication systems have limitations regarding their support for interaction and information selection. Television and telephone companies have attempted to address this limitation with the use of teletext, in the Case of television, and information lines, in the case of the telephone. Both systems attempt to provide a range of information which can be selectively browsed. The limiting factors of these systems are their restricted media types and methods of interaction.

The introduction of communication technologies capable of transmitting multimedia to domestic properties is providing the necessary infrastructure for home users to access a wide range of information services. Home shopping, cookery lessons, home maintenance, and home safety are examples of information which could be made available. Although the examples given are specifically aimed at domestic requirements, the provision of multimedia technology in the home would also provide users with the ability to work from home when required. The potential for multimedia in the home is therefore an important area for investigation. The issues related to computing technology for the home are being addressed in HIVE 78 and IIH 79. HOME s~ meanwhile, is developing standards for the integration of heterogeneous domestic applications.

Science and engineering applications

Whilst a large proportion of research effort has been put into the application of multimedia computing to office and business systems, the scientific and engineering fields are also a prime area for investigation. There is a difference between office-based and technical applications in the quality of the information which must be supported. Multimedia in the office is largely seen as a person to person communication mechanism where audio and video can support decision making and cooperative working through videoconferencing. In this type of application area the resource intensive media


such as audio and video are usually transient and require no analytical processing regarding their content. Since the processing of the audio and video is by the user through eyes and ears, it is possible to reduce the quality in order to lower the burden on processor, communications and storage resources.

Technical multimedia applications are more likely to analyse information to derive conclusions about its content. The use of multimedia may not be person to person, but source to analyser where the analyser may be a human or a digital device. Technical applications, therefore, place much tighter restrictions on the accep- table quality of the information. Research into the requirements of scientific and technical application areas is highly important in fully understanding the nature of the information and the processing to be performed on it 8~. Without this research, future distributed systems may be biased towards supporting office information ~a~ocessing.

A number of research projects are currently investigating the requirements of technical multimedia computing. The majority of research is concerned with the communication issues related to technical multimedia information. RESAM 82 and MARIN 83, for example, are developing application pilots to demonstrate the effectiveness of remote expert support within technical environments. DIMUN 84, DIDAMES 85 and CAR 86, meanwhile, are using multimedia communication to support distributed manufacturing and design. Similar work is also being carried out as part of the BER- KOM 6~ manufacturing project. The PROMISE 87 project is investigating the use of multimedia information as an aid to process control engineers. Multimedia technology aimed at supporting technical information is also having an effect in areas such as agriculture 8s and urban planning 89.

In addition to communication systems, information libraries also form an important part of scientific and technical environments. Quick and easy access to information is of prime importance to any scientist or engineer. A number of research projects, therefore, are attempting to develop information technology which will improve the quality of technical information systems. KWICK 9~ GEOTEL 9t, and CORE 92 are all involved in developing support for on-line multimedia information. The applicability of the Office Document Architecture for technical documents is also important and being considered within the FODATEC 93 project.

Cultural applications

The application of multimedia to office and scientific environments is possibly the most obvious and most applicable because of the technological background of the research teams involved'. The cultural field, however, has an immense potential for multimedia due to its high use of visual information. In comparison to the more traditional areas a number of research organizations are


investigating the possibilities for multimedia technology in this domain. With the range of information types available, it is possible to imagine applications which will ailoxq art galleries and museums to enhance their exhibits with a multimedia information system. The European Museums Network 94, fo'r example, is developing a pilot scheme for displaying exhibits at several sites simultaneously. The number of people able to view these exhibits would therefore increase dramatically.

More specifically for the art world, multimedia computing provides artists with a tool for constructing, storing and displaying their creations. It may not be uncommon to see multimedia workstations in art galleries using the range of available media types to display audio/visual art. Teaching art and supporting design processes will be a future use of multimedia technology. VASARI 95 is aiming to develop a pilot visual arts system for archiving and retrieving images.

Computer Supported Co-operative Working

CSCW 96 has evolved over the last five years to combine the understanding of the nature of group working with the enabling technologies of computer networking, systems support and applications. I.t is now recognized that CSCW is inherently a multi-disciplinary research topic and requires the application of a number of disciplines including sociology, organizational science, 16sychology and computer science.

In work on CSCW, four general classes of cooperative system have emerged97:

�9 Message systems Message systems are descendants of early electronic mail programs which allowed a user using a central machine, to send textual messages to other users on the same machine. As wide area networks designed to support computer communication became more widespread, electronic mail systems increased in complexity and functionality. This development resulted in the formation of a Message Handling System (MHS) model described in the CCITT X40098 series of standards documents. Each message system makes use of a particular message format to transfer information (a message format is often defined as a part of most message standards). Structured message systems are based on the principle of extending the amount of machine processible semantic information available by adding structure to the existing message formats. Systems of this class include the C O S M O S 99 and AMIGO I~176 projects and the Object Lens I~ Stru- del 1~ and ISM l~ systems.

�9 Computer conferenchlg Computer conferencing systems are also a development of the original electronic mail programs. However, structure is imposed in terms of how messages are grouped. A typical computer confer-



encing system consists of a number of groups called conferences, each of which has a set of members and a sequence of messages. Conferences are often arranged so that they individually address a single topic. A user subscribes to those conferences which are of interest. Usually, the system stores information about how far each conference member has read. This information is normally held along with conference messages in one central database rather than the individual mailbox approach used in messaging systems. Examples of this class of systems include Notepad 1~ and COM 1~

�9 Meethlg rooms A typical automated face-to-face meeting room consists of a conference room furnished with a large screen projector, a computer (or network of computers), a number of individual input/voting terminals, and a control terminal. The computer system supporting the meeting often makes use of multi-user software based on some form of analytical decision technique ~~ Software for graphics, vote tally and display also form part of the normal meeting facility. Examples of meetings rooms include the CoLab 1~ Project Nick I~ and the Plann- ing Laboratory at the University of Arizona ~~

�9 Co-attthorhlg and argumentation systems Co-authoring and argumentation systems are a general class of system which aim to support and represent the negotiation and argumentation involved in group working. The cooperative authoring of documents is demonstrative of this class of cooperation where the final generation of a document represents the product of a process of negotiation between authors. This class of systems is characterized by their widespread use of hypertext technology. Argumentation systems include glBIS 11~ and SIBYL TM while coauthoring systems include Quilt 112 and CoAuthor 113.

One of the most interesting aspects of CSCW is the range of application areas which are being proposed. Many of these application areas intrinsically involve multimedia. For example, messaging systems often involve multimedia components, Similarly, conferencing systems can be greatly enhanced by multimedia information. The area of CSCW, therefore, ought to be of great interest to technologists developing multimedia systems. A number of multimedia research projects are looking at the benefits of audio/visual communication in a CSCW environment. IACIS TM, MIAS IIs, Euro- coop ]16, DIME ]17 and MultiG 118 arc all developing interactive environments for audio/visual communication between remote users. Similar work in Cruiser 119, Rapport 12~ and TeleCollab TM is also developing CSCW environments which utilize multimedia communication to improve their effectiveness. APPSN 122 and IPSN1123 are two further projects investigating the use of interactive communication to help people with special

needs. Mobile group working is also going to be important as electronic information becomes more widespread. Telestation TM and MAPS 125 are developing mbbile communication services to support cooperative working and remote access to information.

Note that there is some overlap between the application areas in CSCW and the various application areas discussed throughout this section. This is not surprising as support for group activities is fundamental to many fields of application (office systems, scientific collaboration, etc.). Therefore, it is a mistake to see CSCW as a separate area of application. Rather, the key to CSCW is the multi-disciplinary nature of the subject. Such an approach is valid in many of the application areas described above.

EVALUATION

This review has highlighted the plethora of work in the area &distributed multimedia applications. In addition, the significant impact that multimedia technology can have on a wide range of areas has been demonstrated. However, it is important to introduce a note of caution into the discussion. There are still a number of major problems with the state of the art in distributed multimedia computing. Some of these problems are discussed below;

. �9 Lack o f commercial involvement At present, most of the multimedia applications are at an experimental or research and development stage. Commercial products in multimedia seem a long way away. The only area where products are emerging is in the special case of stand-alone applications, i.e. multimedia applications for single workstations.

�9 Lack" o f digital sohttions Many of the applications listed in this report have been developed on either analogue techno!ogy or on a hybrid analogue]digital solution. Few have ex- perimented with completely digital solutions 126. This has al lowed interesting prototypes to be developed but has deferred many of the technical i problems associated with digital media.

�9 Need for high pelformance experhnental networks Both of the problems discussed above are to a large extent caused by the lack of experimental high speed networking facilities. This is particularly true in the case of wide area networks wh.ere B-ISDN technologies are not yet readily available. This has led to a lack of experience in developing multimedia applications on high speed digital networks and has also delayed commercial interest in the area.

�9 Danger o f bottom-up development Many of the applications that have been developed have been produced by technologists with little emphasis on the end users of the technology. This has meant that a number of multimedia applica-


tions have not been popular with end user communities. This trend can be seen, for example, with videoconferencing applications. There are some notable exceptions to this rule. However, generally, the view of technologists has been predominant in the emergence of applications.

�9 Lack of systems hlfrastructure One of the most noticeable trends is the lack of a systems infrastructure in most of the development work. The vast majority of applications have been developed directly on top of a hardware base with little help being provided in the management of resources across the network. This has meant that most applications are tightly bound to one particular hardware environment and hence are not portable to other configurations. This situation can be compared to the state of the art in parallel processing. At present, in parallel computing, a number of te6hlaiques exist to run specific languages or applications on specific styles of hardware architecture. However, the lack of an agreed system platform has meant that these applications remain special purpose and cannot be ported to other environments. This has severely curtailed the development of parallel processing.

�9 Lack offorttmfor distributed multhnedia compttlblg The work highlighted in this report is split over a number of research communities, e.g. distributed systems, telecommunications and cognitive science, and is also funded from a variety of sources (RACE, ESPRIT, AIM, DELTA, etc.). This has led to a disparity in the field and the lack of a forum to bring together the various skills necessary to develop distributed multimedia applications.

In summary, distributed multimedia computing is an area of great promise. However, the problems highlighted above must be addressed before significant progress can be made.

M U L T I M E D I A A P P L I C A T I O N S U P P O R T SYSTEMS

This application survey has provided an insight into some of the needs of distributed multimedia applications. This work supplements other research aimed at understanding the requirements of multimedia systems. Associated work is looking into the requirements of multimedia applications 127,tzs, multimedia information systems t29'13~ and multimedia communications infrastructures 13t-134. This section discusses the key factors which have emerged from this particular study.

User-oriented design

It is important that systems infrastructures should be carefully tailored for the particular needs of distributed

Distributed mult imedia applications: N Williams and G Blair

multimedia applications. As highlighted above, many existing applications have been developed in a bottom- up manner and hence do not necessarily reflect the needs of the end user. This approach has often led to unnatural and inappropriate designs. Given the demanding nature of multimedia applications, it is particularly important that end users are involved at an early stage of multimedia applications. This concern is one of the major motivations of the CSCW community. It is therefore envisaged that the CSCW community can play an important role in the future of distributed multimedia applications and underlying technologies.

Integration

As discussed previously, the term multimedia encom- passes a wide range of types. In addition, within each type there exists a similar variety of qualities of service (QoS). This variation in information types is illustrated in Figure 1.

As discussed earlier, one of the key challenges of a multimedia system is to integrate the various types and qualities of service within one system framework. This aspect of multimedia is particularly challenging for existing system technologies.

Real-time performance

Multimedia information requires real-time performance in handling a number of media types. This is especially true for the continuous media types such as audio and video. T h e problems in achieving such levels of performance, however, are immense.

In more detail, techniques are required which will deal with multimedia information in real-time in terms of:

�9 storage; �9 processing; �9 transmission.

Again, the issue of performance is demanding for current technologies. Therefore, a great deal of research effort is being directed towards developments of

QoS

CD colour colour full scan

greyscale full scan

mono full scan greyscale

colour s low scan

greyscale s low scan

voice mono mono slow scan

I I I I Type audio image video

Variety of media types text

Figure l



technology to deal with the high performance requirements of multimedia 137' J3s

Dynamic and flexible management

To help meet its performance requirements a multimedia system will need flexibility in the way it utilizes the available resources. In order to achieve this flexibility a high degree of management control will need to be provided. The role.of system management is to allocate requested resources according to a number of quality of service criteria. This task may involve providing a reduced service to applications willing to accept a level of degradation, or the preemption of resources allocated to a lower priority request.

Indeed, the whole question of performance is more fundamental when applied to multimedia systems. Rather than reducing management overheads in an attempt to improve performance, it may well be necessary in multimedia systems to pay the managerial overheads to ensure a minimum level of service. This notion of having sufficient resources only if they are managed correctly is called the 'window of scarcity '139 (see Figure 2).

Essentially, multimedia computing demands respon- sive management in order to optimize the use of resources 14~ Without this optimal management, it will not be possible to realize the more demanding classes of hmltimedia application such as real-time multimedia conferencing.

Specific application demands

Multimedia applications make a number of specific demands of the underlying technology. In particular, it is possible to identify two key areas where multimedia applications require system support: synchronization and groups. These areas are discussed in turn below.

Synchronization The variation in use of multimedia information due to the wide range of possible application areas requires an extensive range of synchronization mechanisms to support multimedia applications TM. Synchronization is required in distributed systems to control the event

interactiw

/:i~-quaSt:

Requh'ements

rernc~

1980 1990 2000

11ardwa~ resou,-ces in yearX

Figure 2 The 'window of scarcity'

orderings and precise timings of multimedia interac- tions ]42. To illustrate the need for synchronization, consider the case of a multimedia presentation. In such a presentation it may to necessary to display captions at various points of the presentation. Similarly, it might be necessary to have an audio soundtrack played together with a related video sequence. In analysing the requirements of multimedia applications, two styles of synchronization can be identified 141" 143.

�9 event-driven synchronization; �9 continuous synchronization.

Event-driven synchronization Event-driven synchronization corresponds to the situation where it is necessary to initiate an action (such as playing back a video sequence) elsewhere in a distributed system. The timing of this action may correspond to a particular point in a document presentation, a user mouse action or a System device reaching a particular state. Event driven synchronization is extremely important in the types of application described in the section on multimedia applications. Many of these applications will be accessing several information sources and sinks and may be associated with several different co-operating users. The management of the information flow between the various components requires notification of system events and user actions. Research is currently investigating mechanisms for supporting event driven

-synchronization in multimedia systems 144.

Conthtttotts synchronization It is also necessary in multimedia systems to specify ongoing relationships across data connections. For example, there is a requirement for a conthlttotts s)'nchronization relationship across two or more real- time channels. This means that sets of real-time presentation devices must be tied together so that they consume data in fixed ratios even when their incoming data originate from different sources. An example of this form of synchronization is a 'lip-sync' relationship between a video transmission and separately stored soundtrack.

Continuous synchronization could be specified in terms of the event driven mechanisms described above. However, with this approach application programmers are required to deal with an unacceptable level of complexity in specifying synchronization algorithms. It is important that application programmers can delegate responsibility for continuous synchronization to a third party. It has been suggested, therefore, that continuous synchronization should be viewed as a transparency issue and algorithms for synchronization be encapsu- lated in managers. Figure 3 illustrates the use of a manager to achieve continuous synchronization transparency.

Groups The emergence of CSCW has highlighted the impor-


Multimedia Application

Register..for_event

Exceptions

Synchronisation Manager

Stream B Figure 3 Achieving synchronization transparency

tance of groups in multimedia applications t45. It is important that support is provided for group interac- tions in systems infrastructures. For example, facilities

-are required to transmit multimedia information to a number of users simultaneously. This is a difficult problem for networking technology particularly in the case of continuous media types. It is also important to provide techniques to co-ordinate groups, e.g. to control access to shared material in a group conference. Present systems do not provide appropriate mechanisms for this style of coordination.

Heterogeneity and standards

Many of the classes of application described above involve users at remote sites inter-working and ex- changing information across a network. In the real world, it is unlikely that all users will share a common infrastructure. It is therefore important to provide support for users to share information across different types of network, different operating systems, and a range of workstations. It is also important in multimedia systems to cater for the wide range of media formats (e.g. PAL and NTSC video formats). Without this ability, multimedia computing will not fulfil its potential as the main component of the next generation of communication technologies.

The normal solution to heterogeneity is to build layered models which factor out system dependent information as you progress upwards through the layers. Over time, these interfaces are normally agreed and standardized across manufacturers. This method of dealing with heterogeneity, however, has an adverse effect on performance due to the processing overheads


involved at each layer. Developers of high performance multimedia systems, therefore, may need an alternative method of approaching this problem.

Standardization is obviously an important aspect in solving heterogeneity and there are a number of existing standards which have been developed regarding the communication of information, e.g. Open Systems Interconnection and Open Distributed Processing. The existing standards, however, are not necessarily applicable to the new technologies which enable multimedia information. It is important, therefore, that these standards develop to support the new types of information available in a distributed system.

Importance of support platforms

In addition to the required technological advances to deal with performance, synchronization, etc, it is also important to provide system platforms to support the development of multimedia applications. The role of such a platform would be to sit between the application programmer and the underlying technology and provide a high level application programming interface (or API). This approach is illustrated in Figure 4.

Such an application platform should mask out complexity introduced by both multimedia and distribution. Furthermore, to provide the confidence required by industry to develop multimedia applications, such a platform ought to be based on existing standards work such as OSI and ODP.

C O N C L U S I O N S

This review has provided a survey of distributed multimedia applications. The opportunities of distributed multimedia computing have been highlighted in such diverse areas as health, education, office systems, the financial sector, retailing, scientific and engineering disciplines, the arts and in the home. The biggest growth areas seem to be. in health, education, and manufacturing where there is a significant interest in multimedia informati6n systems. The report has also

Multimedia Applications -multimedia conferencing, distance learning, medical systems

Application Platform

Multimedia Teclmology - storage, transmission,

processing

Figure 4 An application platform



discussed pr~)blems with the state of the art and highlighted some o f the ma in requirements of distributed mul t imedia applicat ions.

It is argued that there is a need for experimental high- speed networks and for appl icat ion pla t forms to aid development work. The former is necessary to provide experience of the problems of suppor t ing mul t imedia on high-speed networks and to encourage the commercial - izat ion of dis t r ibuted mul t imedia technology. The lat ter is impor t an t to ease the task of mul t imedia developments and to suppor t the portabi l i ty of applicat ions. The development of an appl icat ion p la t form would, however, require the in tegrat ion of a n u m b e r of areas including dis t r ibuted systems, high per formance proto- cols and documen t architectures. S tandardiza t ion is also an impor t an t concern in such a platform, and would involve a n u m b e r of s tandards activities, especially OSI and O D P (and to a certain extent ODA). Such an approach would greatly benefit the field of dis t r ibuted mul t imedia comput ing and contr ibute towards its future success.

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Distributed multimedia applications: A review