Carsten Griwodz

Long-term movie popularity models in video-on-demand systems: or the life of an on-demand movie

Large scale video-on-demand systems require that the serv ers offering the video retrieval and playback services are arranged as a distributed system in order to support a lar ge number of concurrent streams. If such a system is hierarchical, an end-node serv er handles the requests from a particular area, the ne xt server in the hierarchy takes the request over for several end-node servers if those can not answer the request and so on. This architecture pro vides for cost efficiency, reliability and scalability of serv ers. The end-node servers store only a limited set of the o verall available information which changes over time due to user interests. If a video is requested which is not available, this server contacts the next server in the hierarchy. To decide the size and location of the video serv ers and the location of videos in the hierarch y, the access behaviour of users must be considered. Various models for the simulation of user behavior (and thus, of the load induced on the video serv ers) have been presented in the literature. Only a fe w of these models are designed to take long-term effects into account because the basis for most of the models are short-term influences on a single video server and the load on this single machine. In this paper we describe a new user behavior model and show that various assumptions made within other models are unrealistic.

Protecting VoD the easier way

1. ABSTRACT Various on-demand systems require that large numbers of customers are provided with the same multimedia stream content or different but closely related content in short temporary sequence but not at exactly the same time. This includes video on demand and news on demand. A typical approach to increase the performance of such systems is caching. However in current commercial on-demand streaming applications in the Internet caches are used very rarely because a mechanism to protect the content from resale by the cache owners does not exist. A typical solution is to transfer all content via protected unicast transmissions, which is an approach that does not scale. We want to present a trivial scheme that provides similar protection for the content but be used efficiently with multicasting and caching. In this approach, the major part of the video is intentionally corrupted and can be distributed via multicast connections, while the part for reconstruction of the original is delivered to each receiver individually. We propose also means to discourage resale of the multimedia content by customers. One proposal introduces receiver-sided introduction of watermarks into the video, the other uses infrequent corrupt bytes to achieve uniqueness of each copy.

LC-RTP (loss collection RTP): reliability for video caching in the Internet

The increasing amount of audio-visual (AV) content that is offered by web sites leads to a network bandwidth and storage capacity problem. Caching is one of the techniques that can ease this problem. But even in a caching system the distribution of data (i.e. the AV content) should be bandwidth-efficient. Furthermore the delivery to the end-user must regard the restrictions implied by real-time data. This paper describes LC-RTP, an efficient and simple reliable multicast protocol that complies with RTP. Its deployment would require neither changes to the network infrastructure nor to existing end-user presentation software. It provides lossless transmission of AV content into cache servers and concurrently, lossy real-time delivery to end-users using multicast. It achieves reliability by retransmission. The traffic increase is minimal because the transmission of the AV content and any caching will take place while the end-user is served. Support for multicast in the distribution system ensures that all cache servers of a multicast group can cache an AV content while transmitting it to a consumer. Finally we present the results of long distance file transmissions in order to show that LC-RTP performs well and meets the requirements for lossless transmission of AV content.

Exploiting User Behaviour in Prefetching WWW Documents

As the popularity of the World Wide Web increases, the amount of traffic results in major congestion problems for the retrieval of data over wide distances. To react to this, users and browser builders have implemented various prefetching and parallel retrieval mechanisms, which initiate retrieval of documents that may be required later. This additional traffic is even worsening the situation. Since we believe that this will remain the general approach for quite a while, we try to make use of the general technique but try to reduce the destructive effects by retrieving less content which remains finally unread.

Middleware Services for Information Sharing in Mobile Ad-Hoc Networks

Information sharing is a mission critical key element in rescue and emergency operations. Mobile ad-hoc networks (MANETs) could provide a useful infrastructure to support information sharing, but appropriate applications are needed. To facilitate efficient application development for this type of infrastructure, middleware support is needed. In the Ad-Hoc InfoWare project, we are currently developing corresponding middleware services. In this paper, we discuss the application requirements that are imposed onto the middleware services, and we outline our technical approach to address the corresponding challenges. The architecture we propose comprises five main building blocks, namely knowledge management, a local and a distributed event notification service, resource management, and security and privacy management. We indicate design alternatives for these building blocks, identify open problems and relate our approach to the state-of-the-art.

Replication for a distributed multimedia system

Replicating data and services at multiple networked computers increases the service availability of distributed systems. This paper presents the design and implementation architecture of a replication mechanism for a distributed multimedia system medianode which is developed as an infrastructure to share multimedia-enhanced teaching materials among lecture groups. With the replication mechanism, medianode provides enhanced access to presentation materials in both connected and disconnected operation modes. The main contribution of this paper is the identification of new replication requirements in distributed media systems and a multicast-based update propagation mechanism by which not only the update events are signaled, but also the updated data are exchanged between replication managers.

Associating network flows with user and application information

The concept of authenticating users e.g. by means of a login process is very well established and there is no doubt that it is absolutely necessary and helpful in a multiuser environment. Unfortunately specific information about a user originating a data stream or receiving it, is often no longer available at the traversed network nodes. This applies to the even more specific question of what application is used as well. Routers, gateways or firewalls usually have to base their classification of data on IP header inspection or have to try to extract information from the packets payload. We present an approach that works transparently and allows to associate user and application specific information with IP data streams by only slightly modifying components of the operating system environment and infrastructure components. On top of this framework we show usage scenarios for dedicatedly placing copyright information in media content and for an enhancement of the interoperation with the security infrastructure.

Position paper: Internet VoD cache server design

2. INTRODUCTION Internet VoD today is dominated by systems like the Real G2 System [ 131 supporting various low bandwidth formats. The length and especially the quality of current video clips are very limited, and not applicable at all for commercial VoD. One of the major limitations is the necessity to stream the video clip directly from a central server to each client individually, because re-distribution is not established yet. Intranet solutions have existed for a while, they use distributed systems but are typically managed from a central site.

Translating scalable video streams from wide‐area to access networks

Transmitting video over user datagram protocol (UDP) has been considered advantageous because it allows for discarding of packets in favor of retransmissions, and sender‐controlled timing. Using UDP has been criticized because it allows video streams to consume more than their fair share of bandwidth, which is typically associated with the back‐off behavior of transmission control protocol (TCP). TCP‐friendly algorithms are meant as a middle path. However, UDP delivery to end systems may still be prevented by firewalls or for other reasons, and TCP must be used. This in turn suffers from bandwidth fluctuations. Investigates an architecture that separates the transfer of a video stream over long distances. Considers a proxy server to translate the traffic and two straightforward approaches for the translation of a layered video stream transmission from the TCP‐friendly transport protocol to TCP. Does not expect that one of these two approaches is by itself suited for the task, but investigating them will p...

Panel Discussion: How Will Media Distribution Work in the Internet

The panelists discuss the directions that future QoSre search should to support distributed multimedia applications in the Internet, in particular applications that rely on audio and video streaming.While real-time streaming services that are already deployed attract only a minor share of the overall network traffic and have only a minor impact on the network, this is in part due to the distribution infrastructures that are already in place to reduce network and server loads.However, it is questionable whether these infrastructures for noninteractive applications, that rely largely on the regional over-provisioning of resources, will also be capable of supporting future multimedia applications. The panelists discuss their views of the current and future demand for more sophisticated QoSm echanisms and the resulting research issues.