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Telecommunications networks for remote interactive multimedia

Michael Biggar and Carol Scott
Telecom Australia Research Laboratories
Advances in multimedia workstations, software systems, storage for multimedia and user interfaces which allow the presentation of multimedia information have produced an environment in which interactive multimedia systems are developing at a rapid pace. Most current systems are local in their service range, but there will be an increasing demand for long distance multimedia communications. Multimedia communication issues are discussed in this paper. Present day networks go some way towards satisfying the service support requirements of multimedia, but the future Broadband Integrated Services Digital Network (B-ISDN) will ultimately have the capacity and flexibility required to ensure multimedia applications are completely freed from geographical restrictions.

1. Introduction

Recently, there have been considerable advances in the components necessary to permit the development of powerful multimedia applications. These have occurred in the areas of hardware and software, and, to a lesser degree, standards.

Hardware developments have led to the ready availability of 24/32 bit colour display boards for PCs/workstations, allowing the presentation of high quality colour still and moving images, and graphics. "Video in a window" boards complement this by permitting real time video to be presented with other information in an integrated manner. The capability to reproduce high quality sound is also becoming more common. At a more fundamental level, the processing power and backplane speeds of computers permit the manipulation and transfer of large amounts of information, including motion video. Rapid, efficient image compression is possible in a single inexpensive chip. Plug in boards that implement standard motion video coding methods in real time on just a few chips will be available within the next year.

Complementary to advances in PC/Workstation hardware are the software developments that allow these hardware capabilities to be exploited. These include the development of composite documents which combine media (e.g. text and graphics) in the one document. This now allows desktop publishing in which one can actually see what is to be printed. It is also now possible to paste, not just line drawings, but high quality images into other documents, providing a new flexibility for desktop publishing and document preparation. Software systems are emerging that permit shared working by two or more users on the one document. Co-workers can therefore edit the same document interactively and simultaneously. Hypermedia systems offer the potential for information presentation in the most efficient and flexible manner possible in any given application by providing a hierarchical and cross indexed structure to complex multimedia documents. A very recent advance has been the emergence of real time information handling software systems suited to the manipulation of real time information such as audio and video, providing the capability to manipulate (record, store, play, edit, copy, paste) these in the same way as ordinary documents.

Standards are also beginning to be developed to permit the widespread exchange of multimedia information. The ISO is studying stored audio and video systems, database access, multimedia/hypermedia representation, computer graphics systems and others. CCITT covers telecommunication service definition, network support, signalling and coding of communicative audio and video. Relevant activity in CCIR includes the television service definition and CMTT covers standards for coding of broadcast services for transmission.

While some of this standards activity concerns familiar applications, new and vastly different applications will emerge from some of the computer oriented developments. Initially, these will he confined to local applications, using local storage devices and proprietary interfaces and storage formats. At best, some of these could be shared over a Local Area Network (LAN). Increasingly, though, there will be pressure to extend the range of multimedia applications so that even sophisticated multimedia applications, like hypermedia documents, can be transferred across the country and around the world, and information in a variety of formats can be accessed from diverse and remote locations. There will, therefore, be increasing pressure on public telecommunications network providers to support this type of communications.

2. Multimedia communications

The principal features of multimedia communications which impact directly on the telecommunications network are: Clearly, communication networks must provide great flexibility to support the diverse range of services, rates, qualities, configurations, etc. The networks will also have to take account of the inherent link between the service components to ensure that relevant timing constraints can be satisfied and to control the tariffing arrangements for these complex services. Many other issues arise concerning the control of multipoint multimedia applications and the management of information distributed throughout the network.

3. Multimedia communications - network options

Recent developments in telecommunication network evolution are taking us into a future with vastly more transmission capacity available for transmission of a range of digital information.

3.1. Integrated Services Digital Network (ISDN)

The ISDN offers much greater digital capacity than has been available generally before. Multiples of 64 kbit/s are available from this network, and this is sufficient to support limited shared workspace applications, interactive access to image or text/image databases (with transfer times of a few seconds) and even some lower quality video applications. Large files and complex documents could be exchanged over this network much faster than by the traditional low cost modem but, for many multimedia applications, the network would remain a bottleneck to response time.

For some multimedia applications, standard transmission methods have been defined that will support combined data, audio and video over the ISDN. CCITT Rec. H.221 (CCITT, 1990) defines a multiplexing structure for several 64 kbit/s channels used to support audiovisual services defined by other CCITT Recommendations. However, this structure is not intended for universal support of multimedia services.

3.2. Metropolitan Area Networks (MANs)

Offering greater capacity than the 64 kbit/s based ISDN, MANs are intended principally to support LAN-LAN interconnections (Pretty, 1990). Telecom Australia's "FASTPAC" service will be one of the first of these available in the world, and is due for commercial release during 1992. Backbone rates of this network are in the range of tens of Mbit/s to over 100 Mbit/s. Common interfaces will be the main throughput limitation since they will conform to standard LAN systems such as Ethernet or Token Ring (ie. of order 10 Mbit/s).

By providing transparent interconnection between LANs, these networks will provide the infrastructure to allow remote interactive multimedia applications to flourish. The remote systems will appear to be connected to one very large LAN, and the high capacity will ensure that reasonably fast response times are achieved. The MAN standard (IEEE 802.6) is based on fast packet switching methods in which LAN packets are split into a number of segments for transmission and switching. This means that a wide range of service rate demands can be accommodated and that connection control for different applications can be integrated. MANs are seen as a major stepping stone towards the B-ISDN.

3.3. Broadband Integrated Services Digital Network (B-ISDN)

The high speed networking capabilities of the B-ISDN are complementary to the requirements of multimedia services and will enable a variety of new, innovative applications across all market sectors. The B-ISDN, to be introduced in the later half of this decade, will offer User Network Interfaces (UNIs) of 155 or even 620 Mbit/s, sufficient to support even digital High Definition Television (HDTV) applications (Day, 1990).

The use of Asynchronous Transfer Mode (ATM) (again packet based, using short, fixed length packets called cells) as the transport mechanism for the B-ISDN is intended to provide flexibility for the carriage of all known, as well as unforeseen, services. The cell based transport allows adaptation to required service rate requirements and accommodates asymmetrical bandwidth needs easily. Furthermore, low level signalling capabilities permit multiplexing of the different components of a multimedia connection at the cell level. That is, each media has its own cell stream, permitting great flexibility in the routing of the individual media within the network, as well as matching of the cell stream attributes (such as quality of service, and therefore cost) to match the needs of each medium. For example, file transfer data may be much more tolerant of errors or cell losses, because of high level error control, than real time video services.

A discussion of the B-ISDN and its suitability for the support of multimedia is provided in Biggar (1991).

4. B-ISDN Support of interactive multimedia

Assuming that the B-ISDN is the long term home of multimedia communications services, the following subsections provide some discussion of the various issues that arise when considering the demands of multimedia services on the network.

4.1. Service component synchronisation

One of the most obvious requirements for multimedia services is the need to ensure appropriate timing relationships between the components of a multimedia service if they follow paths within the network which could lead to differential delays. This consideration is of particular importance for real time interactive applications.

Examples of multimedia applications in which synchronisation will be most important include audio/video synchronisation for both distributive and communicative video applications, shared workspaces in which it is essential that the same workspace is seen simultaneously by each participant.

4.2. Multipoint working

Extension of multimedia services beyond the self contained PC/Workstation or LAN environment will permit access to remote and diverse databases, and communicative multimedia between sites. One of the major capabilities, however, will be the ability to involve multiple participants. This is already proving to be one of the most important features of the video conferencing service.

A range of issues arise when considering multipoint, multimedia service capabilities. Some of these are:

Other implications will emerge once the diversity of multimedia applications are considered in multipoint environments.

4.3. Service integration

Because multimedia applications encompass not only different media but also multiple grades of the same media, there is a clear requirement to rationalise the various media into common structures, minimising the terminal complexity and maximising its capability to access diverse service types.

The most obvious application of this concept is in the most demanding service type - video. Work is already well advanced in the definition of hierarchical, or layered, video coding architectures that allow interworking across a broad range of services. This will mean that one terminal can accept and present a video signal almost independently of the original source and transmitted resolution, frame rate, etc (Scott, 1990). Complementary studies are required on integration of the various other service components.

4.4. Additional presentation issues

Presentation of the various media components of a multimedia application to a user in a coherent and easily assimilated fashion has already been identified as an important area of ongoing study. However, the provision of multimedia services via a communications network introduces additional issues to be considered.

These issues include: how to provide control of the connections, which may be to different sites, in a manner that is "user friendly"; what tariffing feedback should be provided to allow the user to monitor and "control" the price paid for a particular multimedia connection; and how control of a multimedia connection is to be divided between the user and network operator, and whether the arrangement should vary between media.

4.5. Media conversion/translation

The proliferation of a diverse range of terminals with differing capabilities will introduce interworking issues much wider than just the type of coding method to be used. Terminals able to use different subsets of the possible media will exist, and these may be used to access the same data or even be involved in a multimedia multipoint conference connection. This implies the ability to perform conversion between the media.

An example where this capability might be required is the interrogation of a text based electronic mailbox via an audio only telephone. If this capability is to be permitted, then text to speech conversion will be required somewhere in the link. Another example might be the inclusion of a participant with videophone capability into a multimedia conference where computer graphics files are being exchanged. In this situation, the means to convert the graphics image to standard video signal format would be required.

Investigations are required to determine the range of media conversions which may be required, the feasibility and importance of providing them and the important question of where the conversion should occur. Must it be provided within the network or is it a terminal/database issue?

4.6. Interworking across networks

During the transitional period as the B-ISDN is adopted, and possibly for some considerable time afterwards, some elements of the communication links needed for the support of multimedia applications may be provided over different networks. The various constraints of Metropolitan Area Networks, Narrowband-ISDN, various LANs, etc, will mean that interworking becomes a serious issue.

While interworking across networks is often considered to be solely a network consideration, many service issues also arise, such as how much of the multimedia multiplex should be passed through a network constrained by bit rate or functionality. How much of the decision making process should be given to the user, and for how much will the network intelligence be responsible? How should a multipoint connection be implemented if one of the participants can only be contacted over a low rate network or on a terminal of limited capability (single media)?

Integration of each of the various media is also important in this situation since, for example, the layered "Universal Video Coding" architecture would permit lower rate (and quality) subsets of a video signal to be passed over a rate constrained connection (Tan, 1991).

5. Conclusions

We are now seeing dramatic advances in computing capabilities, and in particular personal computers and workstations, that mean that new forms of information manipulation and presentation become practical. Associated developments in software systems and "hypermedia" applications are providing maximum. potential for use of information in a way that matches the needs of the user and the possible media. A large demand to provide complementary communications capabilities can be expected to free these new information systems from constraints of local access.

At the same time, switched network capacities are increasing (and developments in other areas such as signal processing occurring,) to the point where we can consider support of more traditional media, such as television and high quality audio distribution, that has not been possible on the public network in the past.

These developments indicate the need for an overall framework for the support of these services under the banner of "multimedia" (which can include single media as special cases). Identification of the special requirements of these services, how these can be satisfied, the impact on the network and the most effective means of presenting the service to the customer are important areas for further investigation.

This paper has provided an initial view of the impact that multimedia services may have on communications networks, what the network options and evolutions may be, and a more detailed look at some of the issues that must be considered as the B-ISDN evolves to support this important service category. The B-ISDN has the transmission capacity and flexibility suited to the support of all the components of a multimedia connection, and should be able to deliver very fast response times and a high perceived performance (potentially indistinguishable from operation with local peripherals). However, there remain several important areas to be studied to ensure that this vision can be realised.

6. Acknowledgment

The permission of the Executive General Manager, Telecom Australia Research Laboratories, to publish this paper is acknowledged.

7. References

Biggar, M. and Scott, C. (1991). Multimedia telecommunications services on the B-ISDN. Proceedings Australian Multimedia Communications, Applications and Technology Workshop, Sydney, 1-2 July 1991, pp.162-168.

CCITT (1990). Frame structure for a 64 to 1920 kbit/s channel in audiovisual teleservices. Recommendation H221.

Day, A. and Dorman, D. (1990). Towards an Australian broadband network infrastructure. Telecommunication Journal of Australia, 40(2), 3-14.

Pretty, R. (1990). FASTPAC: Telecom Australia's high speed LAN interconnect network utilising QPSX fast packet switching technology. Proceedings Australian Fast Packet Switching Workshop, Melbourne, 9-11 July 1990, pp. 200-204.

Scott, C., Biggar, M. and Dorman, D. (1990). Getting the Picture - Integrated Video Services in B-ISDN. Telecommunication Journal of Australia, 40(2), 21-25.

Tan, W. (1991). Advanced Video Service Features through the UVC Architecture. Proceedings Australian Broadband Switching and Services Symposium, Sydney, 3-5 July 1991, pp. 8-14.

Authors: M. J. Biggar and C. J. Scott
Telecom Australia Research Laboratories
770 Blackburn Road, Clayton 3168, Victoria, AUSTRALIA

Please cite as: Biggar, M. J. and Scott, C. J. (1992). Telecommunications networks for remote interactive multimedia. In Promaco Conventions (Ed.), Proceedings of the International Interactive Multimedia Symposium, 313-319. Perth, Western Australia, 27-31 January. Promaco Conventions. http://www.aset.org.au/confs/iims/1992/biggar.html

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