End-to-End Mechanisms for Rate-Adaptive Multicast Streaming over the Internet

Continuous media applications over packet-switched networks are becoming more and more popular. Radio stations, for example, already use streaming technology to disseminate their content to users on the Internet, and video streaming services are expected to experience similar popularity. In contrast to traditional television and radio broadcast systems, however, prevalent Internet streaming solutions are based on unicast communication and raise scalability and efficiency issues. Multicast communication provides a promising and viable alternative since it can vastly improve scalability and network efficiency for the aforementioned class of applications. Nevertheless, suitable multicast streaming solutions ready for wide-area deployment are yet to emerge. In this thesis on Rate-Adaptive Multicast Streaming we provide mechanisms for improving multicast video streaming over the Internet. Our solutions address major issues that originate from the requirements for multicast solutions to scale to a large number of receivers and to accommodate the latter's heterogeneity of bandwidth capabilities. Therefore, our work exploits scalable-encoded video and utilizes layered multicast transmission on top of the IP multicast architecture. Choosing a modular design yields flexible techniques that can be integrated as building blocks in different transport and application frameworks. The proposed hybrid set of solutions includes mechanisms for server-side as well as receiver-driven rate adjustment. For the former purpose, we devise an algorithm that optimally stripes the scalable-encoded data into several media quality enhancing layers considering the distribution of receiver bandwidth capabilities. The underlying optimization metric is novel and incorporates transport as well as user aspects. It provides a mapping from each receiver's bandwidth capability onto a utility-based fairness measure. In order to provide means to the server for discovering the bandwidth capability distribution of the active receivers, we design a feedback scheme based on probabilistic polling. It allows to control the feedback traffic within statistical bounds, thus, making the scheme flexible and scaling to very large receiver populations. A key aspect in the design of scalable multicast solutions is the distribution of computational tasks and the reduction of control messages. Consequently, each receiver is responsible for inferring its bandwidth capability without involving the server. Therefore, we adopt and improve the state-of-the-art approach for estimating the fair bandwidth share based on TCP throughput modeling. Extensive simulation results prove the applicability of the modified scheme for estimating the TCP-fair rate of a multicast receiver. Thus, this information can be communicated to the source for rate optimization purposes utilizing our feedback scheme. In addition, it serves also for receiver-driven rate adaptation using a timer-based multicast group subscription strategy. Our novel approach yields a reasonable trade-off between the user demand for smooth video transmission and the network requirement of cooperativeness and responsiveness to congestion indication

Messtechnische Charakterisierung von elektromechanischen Sensoren

Zusammenfassung: Grundgedanke der Studienarbeit war die Frage nach den die Eigenschaften eines Drucksensors kennzeichnenden Größen. Ausgehend von der Fachliteratur und vorhandenen Normen, wurde ein Übertragungs- und Fehlermodell aufgestellt, und die systematischen und zufälligen Kennwerte zusammengetragen. Das Ergebnis ist ein Meßkonzept und eine Excel Auswertevorlage zu einem Meßplatz für Drucksensoren. Zum Ermitteln der Sensorkennwerte sind mehrere Meßablaufsteuerungen in der Software DAGO programmiert und getestet worden. Anhand dieser werden in vier Vorversuchen die Zeiten bestimmt, die die Prüflinge nach einer Meß- bzw. Störgrößenänderung benötigen, um den quasistatischen Zustand zu erreichen. Nach anschließendem Anpassen der Verweilzeiten in der Ablaufsteuerung erfolgt die Messung nach dem aufgestellten Verfahren. Sowohl der Ablauf der Vorversuche, als auch die Hauptmessung stützen sich auf die DIN IEC 770

iShare: Exploiting Opportunistic Ad hoc Connections for Improving Data Download of Cellular Users

This paper presents an Incentive-based Sharing (iShare) protocol that blends cellular and ad hoc networks for content dissemination services. With iShare, mobile users download content from a source via cellular links and at the same time form a mesh ad hoc network for peer-to-peer exchange of content data. The mesh remains robust to network dynamics, minimizes ad hoc communication overhead, and parallelizes the downloading process among mesh members. In order to counter selfish behavior, we apply an efficient and practical "tit-for-tat" incentive mechanism, which exploits proximity and mutual content interest of mobile users. This mechanism becomes particularly effective in the case of network dynamics since we utilize promiscuous and broadcast modes of the ad hoc channel. As a result, our protocol effectively helps to free resources in the cellular network and accelerates the content download for its users. Furthermore, it enables users to continuously obtain data via ad hoc connections during cellular handoff periods and provides multi-homing downloads for groups spanning adjacent cells. We evaluate the performance of iShare by means of simulations and compare it to other content dissemination schemes using cellular broadcast channels, cellular unicast channels, and tree-based protocols. The obtained results show that iShare significantly outperforms alternative approaches and creates a win-win situation by improving performance of both iShare and other mobile users

SliM: Enabling Efficient, Seamless NFV State Migration

Instance migration and scale-in/out operations in network functions virtualization (NFV) require state transfer mechanisms, which are known to cause service degradation through increased jitter and packet loss. Techniques such as packet duplication for state synchronization mitigate this problem, however, they incur significant additional costs. In this paper, we provide a novel interface to the VNF to announce “statelets” for incoming packets, which comprise only the information in the packet which is required for a VNF's internal state change. Based on this interface, we design and implement SliM, a statelet-based framework for seamless VNF migration. First evaluation results show that SliM operates seamlessly at very high dataplane utilization of physical links, up to 3 times the utilization level at which existing approaches are failing due to insufficient bandwidth for state synchronization