Showing papers by "Carsten Griwodz published in 2003"

Towards middleware services for mobile ad-hoc network applications

Abstract: Mobile ad-hoc networks are typically very dynamic networks in terms of available communication partners, network resources, connectivity, etc. Furthermore, the end-user devices are very heterogeneous, ranging from high-end laptops to low-end PDAs and mobile phones. Traditionally, middleware is used to abstract from this heterogeneity and to enable the application programmer to focus on application issues. We propose to develop middleware services that additionally provide services for information sharing in mobile ad-hoc networks, because the possibility to share information is mission critical for many mobile ad-hoc network applications.

Scalable TCP-friendly Video Distribution for Heterogeneous Clients

Abstract: This paper investigates an architecture and implementation for the use of a TCP-friendly protocol in a scalable video distribution system for hierarchically encoded layered video. The design supports a variety of heterogeneous clients, because recent developments have shown that access network and client capabilities differ widely in today's Internet. The distribution system presented here consists of videos servers, proxy caches and clients that make use of a TCP-friendly rate control (TFRC) to perform congestion controlled streaming of layer encoded video. The data transfer protocol of the system is RTP compliant, yet it integrates protocol elements for congestion control with protocols elements for retransmission that is necessary for lossless transfer of contents into proxy caches. The control protocol RTSP is used to negotiate capabilities, such as support for congestion control or retransmission. By tests performed with our experimental platform in a lab test and over the Internet, we show that congestion controlled streaming of layer encoded video through proxy caches is a valid means of supporting heterogeneous clients. We show that filtering of layers depending on a TFRC-controlled permissible bandwidth allows the preferred delivery of the most relevant layers to end-systems while additional layers can be delivered to the cache server. We experiment with uncontrolled delivery from the proxy cache to the client as well, which may result in random loss and bandwidth waste but also a higher goodput, and compare these two approaches.

Storage systems support for multimedia applications

Abstract: Lately, on-demand streaming multimedia applications have become very popular. Contemporary personal computers can handle the load imposed by such multimedia applications on the client side, but the potentially high number of concurrent users accessing a server represents a generic problem. The multimedia storage system is responsible for storage and retrieval of multimedia data from storage devices, and plays a vital role for the performance and scalability of multimedia servers. It deals with issues related to data placement, scheduling, file management, continuous data delivery, buffer management, prefetching, etc., and with the particular demands of multimedia applications, such as real-time characteristics, large file sizes, high data rates, and several data sources. Performing these tasks and supporting these requirements appropriately are burdened by an increasing speed mismatch between processors and the most prolific and affordable storage devices, – magnetic disks –, and by the introduction of new requirements in new multimedia scenarios. In this article, we give a survey of storage system support for continuous media applications and discuss issues related to integration of different mechanisms for the future multimedia storage systems.

Movie placement in a hierarchical CDN with stream merging mechanisms

Abstract: Content distribution networks (CDNs) are a popular service for the dissemination of multimedia content over wide areas. The existance of a centralized administrative structure makes them attractive for the commercial distribution of high quality content. By sharing resources, service providers can implement their services more efficiently than a single content provider who establishes a distribution structure himself. An efficient operation requires cost estimations that allow service providers to determine the dimensioning of their infrastructure and the placement of content in the system. In case of video streaming, distribution mechanisms that exploit multicast, segmented delivery and out-of-order delivery can be applied to merge streams and reduce resource consumption. Several applicable stream merging mechanisms exist in the literature and can be used. We examine three such mechanisms, namely patching, gleaning and prefix caching in a hierarchically organized CDN. We show that a co-optimization of movie placement and stream merging mechanism has an undesirable effect on quality by delivering highly popular movies over longer distances than less popular ones. We explore and compare two approaches for overcoming this problem by qualifying the placement optimization with additional conditions. We find that in this case, straight-forward sorting is a good solution.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Towards scalable and affordable content distribution services

Abstract: Absrmcr- Content Distribution Networlts (CDNs) are bred On a static infrastructure, and caching and replication in CUNs are performed in a static manner. We argue that it is necessary to design future CDNs in such s aay that they are scalable tu reach enough customers, their costs are kept low, and they provide a Quality-of.-Service that satisfies the client requirements. To reach these goals, more flexibility is needed in CDNa. Flexibility will enrhle CDNs to perform faster and better decisions for caching and replication, and it will reduce the aniount of inanuul interwnlion that is necessary to manage and maintain the CDN. In this paper, we discuss the application of Peer-to-Peer mechanism in CDNs that support advanced caching and replication strategies and their combination with a dynamic QoS management hierarchy to reach the needed flexihility in CDNs.