an architecture for adaptive multimedia content delivery

New Generation Computing, 18(2000)375-389 Ohmsha, Ltd. and Springer-Verlag

COMPUTING � 9 Ltd. 2000

An Architecture for Adaptive Multimedia Content Delivery

K a n a m e H A R U M O T O Cybermedia Center, Osaka Universi~ 5-1 Mihogaoka, Ibaraki, Osaka 567-0047, JAPAN harumoto�9 o s a k a - u , ac . j p

Tadashi N A K A N O Department of lnformation Systems Engineering Graduate School of Engineering, Osaka Universi~ 2-1 Yamadaoka, Suita, Osaka 565-0871, JAPAN t n a k a n o ~ i s e , eng . o s a k a - u , ac . j p

Shinji SHIMOJO Cybermedia Center, Osaka Universi~. 5-1 Mihogaoka, Ibaraki, Osaka 567-0047, JAPAN sh imoj o~cmc, o s a k a - u , ac . j p

Received 18 January 2000 Revised manuscript received 20 April 2000

Abstract In this paper, we propose an architecture for multimedia content delivery considering Quality of Service (QoS), based on both the policy-based network and the best-effort network. The architecture consists of four fundamental elements: multimedia content model, application level QoS policy, QoS adaptation mechanism, and delivery mechanism. Applications based on current architecture loses their meaning by drastically degrading quality when network congestion occurs. Despite of this all-or-nothing architecture, applications based on our adaptive architecture can reduce its quality and then negotiate with the network entity, keeping its quality measure as much as possible even when network congestion occurs. We may consider a quality measure for Web pages, total page transmission time, and transmission order of inline objects as a segregation. We then define a language to specify application level QoS policies for Web pages and implement a delivery mechanism and a QoS adaptation mechanism to fulfill these policies.

Keywords: Multimedia Content, Quality of Service, Content Delivery.

376 K. Harumoto, T. Nakano and S. Shimojo

w Introduction The characteristics of data which database systems must handle are dras-

tically changing. Database systems must now deal with voice, video, image and spatial data in addition to text and numerical data. The sizes of these new types of da ta are generally much larger than that of text and numerical data, and they have the notions of quality and timeliness which are not found in text and numerical data. Database systems are also dealing with distributed data because of the evolution of the Internet. The distributed multimedia applications such as the W W W (World Wide Web), VoD (Video on Demand) systems, and NVR (Networked Virtual Reality) systems are examples of such systems.

On the other hand, computer networks are diversifying their characteristics. Regarding communication speed, gigabit networks are becoming available. Furthermore, home and mobile users can now easily access the Internet via dial- up links, where typical communication speed is expressed in kilobit per second. The emergence of QoS enabled networks is another important change in network systems. In traditional networks, there is no guarantee of data transmission rate because they only support best-effort traffic. In QoS enabled networks, however, network resources can be reserved for data transmission, so that we can have a guaranteed data transmission rate.

These drastic changes in database systems and computer networks require tha t we reconsider data distribution architecture for multimedia content, because the quality of distributed multimedia applications, such as the WWW, VoD systems, and NVR systems largely depends on available network and system resources. If the quality of the contents is deteriorated or it takes a long time to transmit, they would lose their meaning.

The application behavior for multimedia content delivery depends on the type of service provided by the underlying network. On the best-effort type network, there is no guarantee of resources. If enough network resource cannot be provided, the content quality is reduced.

On the other hand, on the guaranteed-service network, the quality is as- sured once the application is admitted. An application simply requests necessary network resource to achieve its best quality. If the requested network resource is not available, the application is rejected. This model suits high-quality mul- t imedia content such as on-demand movies in pay-per-view format.

However, this all-or-nothing model is too limiting for most multimedia content delivery applications. If the application can accept reduced quality and request smaller amounts of network resource, its execution is more likely to succeed. Even on the best-effort network, an application could at tempt to retain quality as much as possible by estimating current available network resources and adapt by reducing its quality. This process is called adaptation.

In terms of system architecture, many studies of QoS architecture are ongoing. 1.s) Some of them provide a notion of "QoS renegotiation," that is, the end system renegotiates its request to other end system when the at tempt trial is denied. However, it is unclear in these studies how an application uses network services for renegotiation. This is partly because at that time, there was little

An Architecture for Adaptive Multimedia Content Delivery 377

foundation for interaction between a QoS enabled network and an application. Recent discussion of a policy framework 10) in I E T F gives a concise foundation of QoS architecture, which is described later. To construct an application based on QoS architecture, however, further discussion should be made to determine how an application adapts to a policy-based network.

For adaptation, the quality deterioration may differ on each application. A movie trailer, for example, could not be shown under a certain frame rate. Also there are multiple ways to reduce an application's quality, depending on network resources admitted.

Therefore, the s t ra tegy for adaptive mult imedia content delivery should be defined along with the application itself. An adapta t ion policy is well suited for QoS provisioning networks, such as IntServ or DiffServ. On these policy- based networks, there are rising expectations that a certain amount of network resources could be given to a class of applications. Therefore, we can expect a concise application adapta t ion behavior by specifying a policy. By preparing a policy on how to adapt a given network resource, the quality of mult imedia content can be guaranteed. In contrast, it is difficult to specify these strategies for the best-effort network because network resources cannot be estimated. By specifying a policy for the adaptat ion, however, an application can reduce its quality.

To keep distributed mult imedia content delivery as effective as possible, an application policy should be introduced. In this paper, we introduce an application level policy for adapta t ion and we propose an architecture for mult imedia content delivery considering QoS. Then, we show an application of the proposed architecture to the content delivery in the WWW, which we have constructed based on the proposed architecture. In the delivery of mult imedia content, it is significant to introduce a notion of QoS for continuous media such as video and sound because their qualities are greatly affected by network resources. How- ever, the introduction of QoS notion is also significant for rather static media such as Web pages. Although we describe only one application in this paper, the architecture could be applicable to the general composite media, including continuous media.

w Architecture for Adaptive Multimedia Content Delivery

2.1 Policy-Based Network Both system resources and network resources dominate an application's

quality. However, in this paper, we concentrate only on network resources because we are interested in interaction of the end system and networks.

Considering architecture for multimedia content delivery, there are three participants: a server, a client, and a network. Data is delivered at the client's request. In the case of mult imedia content delivery, the network resources such as bandwidth must be maintained between the server and the client. To guarantee network resources, each router in the pa th between the server and the client should understand how much resource needs to be given to the application.


Content Bandwidth ~ Client Server _.~t~o~ Broker I - - J policy

/ /signaling~ ~

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......... , ~ z ~:: :: ii::i:: ::ii i:: iiii ?: ii~ii ii iii ?:iil ii ii ::iiii ilili::ii,:ii il.i i ii ili iiiiiiiil ii ili iiiilililili::ili:: ii ii::.i i i i i:: iiiilil i :.iiii i:. :.i i ili:i:.ii:: ::: ............ ................. twork

Fig. 1 The Policy-based Network

Current ly , the discussion on provisioning QoS in the In te rne t is jus t under way. The re are two proposed mechanisms in I E T F for provisioning QoS in the In terne t : the in tegra ted services (IntServ) 11) and the differentiated services (DiffServ) 2). In tServ a rch i tec ture can guarantee abso lu te quali ty by using R S V P (resource ReSerVat ion Protocol ) . DiffServ archi tec ture , which provides QoS on hop -by -hop basis, is a t t r ac t ing growing a t ten t ion in the In te rne t communi ty . Dit tServ archi tec ture has the advan tage of its scalabil i ty because it does not deal wi th per-flow traffic but deals with aggregate traffic, and it is sui table for the s t ruc tu re of the In ternet . On DiffServ archi tec ture , a P r e m i u m service can be p rov ided for desired flows. 6) By using In tServ or DiffServ archi tecture , a ne twork service can be guaran teed . Al though b o t h In tServ and DitPServ have mechan i sms to provide QoS, the m a n a g e m e n t of ne twork resources is necessary. W i t h o u t the rigid m a n a g e m e n t of network resources, even these mechan i sms canno t guaran tee QoS.

Therefore , for the m a n a g e m e n t of ne twork resources, a Bandwid th Broker (BB) is proposed 1~ On a pol icy-based network, there are BBs which m a n a g e resources. A policy de te rmines how much of a ne twork ' s resources can be given to a specific appl icat ion execut ion. A BB pushes policies to the routers in its domain . Figure 1 shows this m a n a g e m e n t flow.

Therefore , on the pol icy-based network, the following scenario could oc- cur. First , an appl icat ion requests a certain a m o u n t of ne twork resource to achieve the best quality. I f the policy server admi t s the request based on the cur rent available resources, an appl icat ion could run on its bes t quality. How- ever, if it is not admi t ted , then, the appl icat ion s ta r t s negot ia t ing with the pol icy server for an adapta t ion . T h a t is, the appl icat ion reduces its qual i ty and requests a smal ler amoun t of the ne twork resources. Once admi t t ed , an appl icat ion mus t keep its proposed amoun t of ne twork resource to fit the one it is given.

On the best-effort type network, there is no pol icy server to manage the ne twork resources and no guaran tee of resources. Therefore , the appl ica t ion itself moni to rs the current avai lable network resource and adap t s to the qual i ty p e r m i t t e d by t ha t resources. I f the network resource changes, the appl ica t ion changes its qual i ty to fit to the available resources.

An Architecture for Adaptive Mult imedia Content Delivery 379

2.2 Quality Measures for Adaptation of the Multimedia Content Delivery To make multimedia content delivery such as the W W W adaptive, we

should introduce quality measures for adaptation, tha t is, what we should op- timize. Therefore, we consider rather static media as dynamic and continuous media and introduce the quality measures. That is, we consider the time of the presentation, the order of the content presentation, and their resolution as quality measures of the whole presentation. In the WWW, the total time to present a whole page depends largely on how much bandwidth we can get as well as the volume of the content. If it gets long, a user gets frustrated. This

can be considered as a quality measure of that page. The other important measure for quality is a notion of segregation. That

is, we define what is important and what is not among the multimedia components. The content considered more important should be separated from the rest. Segregation can be defined by either authors or users. In the current description language for the WWW, i.e., HTML (Hypertext Markup Language), we cannot define an order of the content to be presented. However, some content may be more important than others in that page, and a user or an author may

want to define the order of the contents to be presented. Quality measures are used for adaptation. Although we respect all the

quality measures, some are implemented as measures to be optimized and some as constraints.

2.3 Functional Models Considering the above quality measures, we propose our architecture for

multimedia content delivery in Fig. 2. We should note that this figure shows only a functional model. This model does not imply which function should be implemented on which part - - a server, a client or a network.

Our proposed architecture consists of four fundamental elements:

�9 multimedia content model, �9 application level QoS policy (a-policy), �9 delivery mechanism, and �9 QoS adaptation mechanism.

[ 1 ] Multimedia Content Model Multimedia content is modeled and represented as a composition of mul-

tiple media components. For example, in Web pages, text, images, and other types of data are combined in an HTML document. A multimedia content model may define three relations among objects: a composite relation, a spatial relation, and a time/synchronization relation. HTML documents do not include time/synchronization relation. If the multimedia content contains continuous media such as video or sound, they must ii~elude time/synchronization information in a similar way to SMIL? ) These relations result in fundamental constraints for adaptation.

Segregation of multimedia components must address their multiple variants in quality. For example, an image may have variants representing different


request p QOSmechanismadaptation i qchoose/select m status report ~deliver request

Delivery i mechanism

Multimedia contents model data model time model quality model

Fig. 2 The Content Delivery Architecture

resolutions or format, and a video may have variants representing different frames per second. Since these variants require different amounts of a network resource, we can find an appropriate variant suite for available resource. These variants are often called LeD (Level of Detail). Further, we could interchange media with the same semantics. For example, we could replace an image with text that has the same meaning when sufficient network resource could not be given. This is called alternative. If a multimedia content model contains LeD and alternative, we could use them to implement segregation. In the case of VRML, it contains LeD. In case these are not contained in the content model, we should expand the model for adaptation. As described later, we expand HTML for segregation, such as different file formats.

[ 2 ] Application Level QoS Policy To adapt to the available network resource, we must define which quality

measure is implemented, how it is implemented, and which component should be segregated. This is called application level policy or a-policy.

An a-policy can be represented in the form of description or can be implemented within the program. For example, if we prefer to transfer a specific image earlier than others in a Web page, such segregation is written within an HTML document as described in section 3. The waiting time for an image to be displayed is defined as a constraints in our expanded HTML. On the other hand, in navigating the NVR system, since we prefer to see closer objects in more detail than other objects, this policy is implemented in the form of a program of the NVR system.

[ 3 ] Delivery Mechanism Between a server and a client, there exists a mechanism which delivers

multimedia content. The primary function of the delivery mechanism in our case is a serialization of multiple content. The serialization is a flow scheduling for static media, and means that we should put some order to the multiple components in the multimedia content. The order is made considering the seg-


regation. On transmission of mult imedia content, QoS control mechanism such as

flow shaping and flow scheduling, as shown in 3), should be done. However, on the policy-based network, because a certain amount of a network resource could be maintained, only the flow shaping should be done.

[ 4 ] QoS Adaptation Mechanism On top of the delivery mechanism, an adaptat ion mechanism exists to con-

trol QoS of the multimedia content. The QoS adaptat ion mechanism interacts with network services in different fashion, depending on the types of services provided. On the best-effort network, a QoS adapta t ion mechanism can only est imate current available network resource, par t ly by monitoring a response t ime or a packet loss ratio. Based on this estimation, it chooses an appropriate combination of components considering the a-policy of the multimedia content.

On the policy-based network, a QoS adaptat ion mechanism requests a certain amount of network resource to achieve the best quality. If this request can be admit ted by the policy server, an application could deliver its contents on its best quality. However, if it is not admitted, the QoS adaptat ion mechanism starts negotiating with the policy server for an adaptat ion. Tha t is, it reduces its quality and requests a smaller amount of the network resource.

w Adaptat ion Architecture for the W W W The World Wide Web (WWW) is the most popular mechanism to dis-

t r ibute mult imedia content on the Internet. In the W W W , impressive infor- mat ion can be provided by embedding a large number of inline objects such as still images, animated images, and background sounds in a Web page. However, if the available network bandwidth between the client and the Web server is insufficient, it takes a long t ime for a client to get all the inline objects in the Web page. Users often terminate the transmission of the Web page before it is completed, which can cause a great loss to companies which do business on the W W W . To solve this problem, an effective content delivery mechanism is required.

We may consider a quality measure for Web pages, total page transmission time, 4) and transmission order of inline objects 9) as a segregation. Because users may intentionally terminate the transmission of a Web page if it takes a long t ime to get all of the page's contents, total page transmission t ime should be controlled so that users are not irritated. Controlling transmission order of inline objects is also important because inline objects in a Web page generally appear on Web browsers in the order of transmission. By controlling transmission order of inline objects, we can obtain the following advantages:

�9 reduction of user-perceived latency, �9 impressive advertisement, and �9 effective presentation.

In the following subsections, we describe these policies, and how we can


use them to implement a QoS adaptat ion mechanism for the WWW.

3.1 Multimedia Content Model Multimedia content model for W W W is HTML. It describes page struc-

ture containing many graphics. In order to serve Web pages to clients with a variety of network bandwidths, the server must prepare a number of object variants in quality to meet the transmission t ime constraint. However, since prepar ing multiple variants beforehand will result in consumption of the storage of the server, we adopt the on-the-fly model. T h a t is, whenever the server receives a request for a Web page from a client, it performs the quality control of inline objects. The server can, however, arrange a cache storage to store the quality-controlled objects, which will alleviate the server 's computat ion load.

3.2 Describing A-policy for the WWW Here, we define a language to specify a-policy for W W W pages, the total

transmission t ime and transmission order of inline objects. In the proposed language, content providers can describe the total transmission time threshold and the transmission order of inline objects in the head section of the H T M L document. More detailed specifications can be described within the inline objects themselves.

[ 1 ] Specifying Transmission Time Controlling Policy

Transmission Time Threshold The transmission t ime threshold is specified in the head section of the HTML document as follows.

<head> <meta name="TransmissionTime" content="30"> </head>

This specification states that the content author wishes to transmit the page in about 30 seconds.

Priority of Images In order to deliver the Web page in the specified transmission t ime threshold, the quality of inline objects, especially of still images, may have to be reduced. In this case, content providers should be allowed to specify the priority of each inline image. For example, in a page describing a product lineup of a company, the photo images of new products should be given higher priority compared with the images of other products. The priority of the image quality can be specified as follows.

<img src="foo.jpg" priority="High"> <img src="bar.jpg" priority="Low">

In this example, the quality of the image foo.jpg will be preserved in comparison with tha t of bar.jpg.


Format Conversion The image formats commonly used in the W W W are J P E G and GIF. We can control the quality of JPEG images by means of the parameter called the quality-factor, by which we can reduce the data size of the image significantly while maintaining the image quality.

We cannot control the quality of GIF images in such a way. To reduce the da ta size of a GIF image, we can reduce the number of colors used or reduce the resolution of the image; these conversions may result in a low-quality image, however. Thus, we allow content providers to specify that the image can be converted to a JPEG image so that its quality can be controlled.

The following specification allows the format conversion from GIF to J PEG when the image quality becomes very low.

<img src="foo.gif" allow-"ToJpegIfLowQuality">

As for animated GIF images, the content author can control quality by reducing the number of frames by the following specification.

<img src="bar.gif" allow-"ReduceFrameRate">

To apply these specifications to every image in the page, the author can write the following in the head section of the Web page.

<head> <meta name="AllowAll" </head>

content="ToJpegIfLowQuality">

[ 2 ] Specifying Transmission Order Controlling Policy Each inline object whose time order is specified must be assigned a unique

identifier in the HTML document, and is referred to with the identifier in the description of the transmission order. The transmission order is specified by four elements: seq (sequential transmission), par (parallel transmission), xfer (transfer of an inline object), and dto (description of transmission order). Below we describe the syntax and semantics of these elements along with their usage through examples.

The seq Element A seq element indicates sequential transmission of inline objects. It must contain one or more xfer elements. The following example indicates that three objects with identifiers A, B, and C are to be transferred in sequential order.

<seq> <xfer object="A"/> <xfer object="B"/> <xfer object="C"/>

</seq>

384 K. H a r u m o t o , T. N a k a n o a n d S. S h i m o j o

The pa r Element A par element indicates parallel transmission of inline objects. The description is almost the same as the seq element. However, this element must have the slice attr ibute, whose meaning is explained later. The following example indicates that three objects with identifiers A, B, and C are to be transferred in parallel.

<par slice="lO"> <xfer object="A"/> <xfer object="B"/> <xfer object="C"/>

</par>

The xfer Element An xfer element indicates transfer of an object identified by the value of the object at tr ibute, and it can also be used to specify transfer of a fragment of the object. To specify a partial transmission, either of the following a t t r ibutes can be used.

�9 wolume at tr ibute specifies the volume of the fragment to be transferred. �9 range at tr ibute specifies the range of the fragment to be transferred.

We show two examples of the effective use of the partial transmission.

�9 Suppose tha t there is a Web page containing a main image A and two images for advertisement, B and C. If we first transfer half of the segment of A, and then transfer B and C, and lastly transfer the rest of A, we can provide the information for advertisement effectively while keeping user's a t tent ion to the page. Such a transmission order can be described as follows.

<seq> <xfer object="A" volume="50%"/> <xfer object="B"/> <xfer ob ject="C"/> <xfer object="A '' volume="50%"/>

</seq>

�9 As for an animated GIF image, t ransmit t ing the first frame is enough to complete the presentation of the Web page. Thus, the remaining frames can be t ransmit ted after all the other images have been transmitted. Such a transmission order is described as follows.

<seq> <xfer object="A" volume="if"/> <xfer ob ject="B"/> <xfer object="C"/> <xfer object="A" volume="rest"/>

</seq>

The dto Element A dto element encloses the transmission order description. This element can have the following attributes:


�9 rest attribute The rest attribute is used to specify the transmission order of inline objects for which the transmission order is not specified. Those inline objects will be transmitted after the inline objects for which the transmission order is specified, either in sequential order or in parallel, according to the value of this attribute. The possible values are 'seq' and 'par'.

�9 ca ch e attr ibute If a client has some cached copies of the inline objects, there are two ways to present them in the client's Web browser. One is to present them according to the specified transmission order, and the other is to present them immediately regardless of the specification. By using the cache attribute, content providers can control the presentation order of cached copies. The possible values are 'ordered' and 'immediate'.

[ 3 ] Example Figure 3 presents an example of the proposed specification. We show how

the inline objects are t ransmit ted based on the description. This W W W page contains one important image and one picture consisting of three interlaced images and one animated image. Moreover, a background sound and many other images are embedded. Based on the description, the important image is transferred first. Next, four partial images are transferred in parallel so that it gives the users a quick preview of the full picture. After that, the background sound, the rest of the frames of the animated image and other images whose transmission order is not specified are transferred sequentially. Note that the quality of these inline objects may be reduced if they cannot be delivered in the specified transmission time threshold, i.e., within 30 seconds. In such a case, however, the quality of the important image is preserved in comparison with other objects.

3.3 QoS Adaptation Mechanism To control the quality of Web pages, the server must know the effective

network bandwidth between the server and the client. If a QoS enabled network is available, network bandwidth can be reserved for the page transmission. In this case, the reserved bandwidth can be regarded as the effective network bandwidth. If a best-effort type of service is used for the page transmission, the effective network bandwidth is estimated by monitoring the data transmission between the server and the client. Because the available network bandwidth may vary from moment to moment in the current best-effort type internet, the server must continuously monitor the transmission.

Once the effective bandwidth is estimated, the server calculates the reduction rate R from the total amount of data to be transmitted (D), the specified transmission time threshold (T), and the estimated network bandwidth (B) by the following formula:

T • R - - - -

D


<html> <meta name="TransmissionTime" content="30"> <meta name:"AllowAll" content="ToJpegIfLowQuality"> <dto rest="par" cache="ordered">

<seq> <xfer ob ject="B"/> <par slice=" i0">

<xfer object:"C" volume="If"/> <xfer ob ject:"m"/> <xfer object="E"/> <xfer ob ject="F"/>

</par> <xfer ob ject="A"/> <xfer object="C" volume="rest"/>

</seq> </dto> <bgsound src="bgm.midi" id="A">

</head> <body>

<img src="important.jpg" id="B" priority="High"> <img src="animation.gif" id="C"> <img src="interlacel.gif" id="D"> <img src="interlace2.gif" id="E"> <img src="interlace3.gif" id="F">

</body> </html>

Fig. 3 Example of the Specif ication

If R < 1, the server reduces the file size of each image by controlling its quality so that the sum of the data volume to be transmitted becomes about R t imes the sum of the data volume of the original image files.

3.4 Delivery Mechanism Since it is difficult to synchronize the transmissions on multiple T C P

connections, we decided to use a single connection to implement the transmission order control. To transfer multiple inline objects over a single TCP connection with the specified order, we must rearrange the bytes of the inline objects. We call such a rearrangement the transmission serialization.

Figure 4 illustrates the way to serialize the transmission of inline objects in which the transmission order is specified. A parallel transmission is emulated by subdividing the transmission of the contained elements into multiple, equal-size pieces and transmitting them alternately from the front. The number of subdi- vided pieces (s) is determined by the slice value which is specified as an attribute of the par element. If the slice value is specified as a simple integer value (e.g., "5"), it is directly used as the number of subdivision. If it is specified as a t ime


Fig. 4 Transmiss ion Serialization

value (e.g., "500ms"), the number of subdivision is calculated from the specified time (t), the total size of the contained elements (d), and the effective network bandwidth between the server and the client (B) by the following formula:

d S - t x B"

To realize the serialized transmission of inline objects, we can employ range requests (also known as partial GET) of HTTP/1 .1 . However, the overhead is not negligible when the specification contains parallel transmissions. In that case, the browser needs to learn the file size of every inline object to per- form the transmission serialization. In addition, the total size of range requests becomes large in proportion to the slice value.

To reduce the overhead, we have proposed a new protocol, HTSP (Hy- pertext Streaming Protocol), to realize the transmission order control of inline objects. 9) The new method, MGET, is introduced in HTSP to retrieve multiple objects with specified order by a single request.

w Conclusion In this paper, we have proposed architecture for adaptive multimedia

content delivery whose four basic elements are multimedia content model, application level QoS policy (a-policy), delivery mechanism, and QoS adaptation mechanism. We have presented the application of the proposed architecture to the content delivery in the WWW. Our proposed architecture can also be applied to other systems such as NVR. 3~

An a-policy gives direction on how we can reduce an application's presentation quality under limited system and network resources, based on the segregation of components. However, our QoS adaptation mechanism tries to retain the original semantics of presentation in the W W W or the NVR system as much as possible. In a more advanced QoS adaptation mechanism, we could change the semantics by replacing presented information itself. A notion called InfoLoD has been proposed as such a mechanism to control the detail of presented information by LoD. ~)

As the standardization of DiffServ architecture in the IETF proceeds, the service model of the policy-based network becomes clear. Then we can build a more concise architecture for adaptive multimedia content delivery.


Acknowledgements This research was supported by "Research for the Future" Program of

Japan Society for the Promotion of Science under the Project "Advanced Mul- t imedia Content Processing" (Project No. JSPS-RFTF97P00501).

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Kaname Harumoto, Ph.D.: He received the M.E. and Ph.D.(Eng.) degrees from Osaka University, Osaka, Japan, in 1994 and 1998, respectively. From 1994 through 1999, he was with the Depart- ment of Information Systems Engineering, Graduate School of Engineering, Osaka University. Since November 1999, he has been an Assistant Professor in Computat ion Center (currently, the name has changed to Cybermedia Center), Osaka University. His research interests include database systems, especially in advanced network environments. He is a member of IEEE.

Tadashi Nakano: He received the B.E. degree from Osaka Uni- versity in 1999. Currently, he is a Ph.D. candidate in Gradua te School of Engineering, Osaka University. His current research interests include multimedia content delivery architecture.

Shinji SHIMOJO, Ph.D.: He received the M.E. and a Dr.E. degrees from Osaka University in 1983 and 1986, respectively. From 1986 through 1989, he was an Assistant Professor in the Depart- ment of Information and Computer Sciences, Faculty of Engi- neering Science, Osaka University. From 1989 through 1998~ he was an Associate Professor and since 1998, he has been a Profes- sor in Computat ion Center (currently, the name has changed to Cybermedia Center), Osaka University. He was engaged in the project of object-oriented multimedia presentation system called Harmony. His current interests cover wide diversity of multimedia applications such as News On Demand System, mult imedia database and networked virtual reality. He is a member of ACM and IEEE.

an architecture for adaptive multimedia content delivery

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