Evaluating the networking performance of Linux-based home router platforms for multimedia services

ABSTRACT Wireless router platforms based on the Linux operating system are becoming popular in consumers' home networks. The transmission of multimedia data or their use as mediaaware network elements imposes high traffic and computational loads on these devices. Thus, it is interesting to evaluate the networking and processing capabilities of such home router platforms in order to assess their usefulness for improved multimedia services such as in-network H.264/SVC video stream adaptation. This paper presents a performance evaluation of three home router platforms representative for low-end, mid-range, and high-end devices. The scope of the evaluation is the performance of the Linux networking stack on these routers; results for both application-layer (TCP and UDP) transmission and kernel-level (UDP) traffic routing are given. The results show that both TCP and UDP throughputs are significantly below (less than half of) the outgoing (wired) links' nominal capacities and depend very much on the sizes of the transmitted data blocks. This clearly indicates that the networking performance is limited by the platforms' processing capabilities and the lack of mechanisms that offload networking tasks from the CPUs. This behaviour cannot be observed on today's PC systems and has to be considered when deploying multimedia services on these network devices. Furthermore, a detailed analysis of the Linux networking stack reveals that the performance is heavily impacted by the netfilter code, even when no packet filtering or network address translation is being performed. Considerable performance gains can be achieved when this netfilter code is bypassed

No Conclusive Evidence for Transits of Proxima b in MOST photometry

The analysis of Proxima Centauri's radial velocities recently led Anglada-Escud\'e et al. (2016) to claim the presence of a low mass planet orbiting the Sun's nearest star once every 11.2 days. Although the a-priori probability that Proxima b transits its parent star is just 1.5%, the potential impact of such a discovery would be considerable. Independent of recent radial velocity efforts, we observed Proxima Centauri for 12.5 days in 2014 and 31 days in 2015 with the MOST space telescope. We report here that we cannot make a compelling case that Proxima b transits in our precise photometric time series. Imposing an informative prior on the period and phase, we do detect a candidate signal with the expected depth. However, perturbing the phase prior across 100 evenly spaced intervals reveals one strong false-positive and one weaker instance. We estimate a false-positive rate of at least a few percent and a much higher false-negative rate of 20-40%, likely caused by the very high flare rate of Proxima Centauri. Comparing our candidate signal to HATSouth ground-based photometry reveals that the signal is somewhat, but not conclusively, disfavored (1-2 sigmas) leading us to argue that the signal is most likely spurious. We expect that infrared photometric follow-up could more conclusively test the existence of this candidate signal, owing to the suppression of flare activity and the impressive infrared brightness of the parent star.Comment: Accepted to ApJ. Posterior samples, MOST photometry and HATSouth photometry are all available at https://github.com/CoolWorlds/Proxim

Leichtgewichtige Konfigurationsmanagement-Plattform für IT-Infrastrukturen

Robert KuschnigZsfassung in engl. SpracheKlagenfurt, Alpen-Adria-Univ., Dipl.-Arb., 2006KB2006 26OeBB(VLID)241623

Congestion-aware quality-adaptive streaming of scalable video

WÃ$hrend das Internet anfangs hauptsÃ$chlich fÃr die Verbreitung von Informationen genutzt wurde, konnten mit der flÃ$chendeckenden EinfÃhrung von Breitband-Internet-AnschlÃssen auch neue GeschÃ$ftsfelder erschlossen werden. Eine dieser neuen Anwendungen ist Internet-Video-Streaming. Doch die Ébertragung groÃer Datenmengen Ãber das Internet ist nicht unproblematisch, da es im Internet keine MÃglichkeiten zur Sicherstellung von DienstgÃte gibt. Die daraus resultierenden Probleme sind groÃe Schwankungen in der verfÃgbaren Bandbreite und der Paketlatenz, Paketverlust und Éberlastung des Netzwerkes. Diese Rahmenbedingungen erschweren einen reibungslosen Videokonsum und machen Internet-Video-Streaming zu einem sehr interessanten Forschungsgebiet. Das Transmission Control Protocol (TCP) ist das Standardprotokoll im Internet fÃr zuverlÃ$ssige DatenÃbertragung mit Éberlaststeuerung. Im Besonderen wurde das Design von TCP auf die BedÃrfnisse der zuverlÃ$ssigen DatenÃbertragung im Internet abgestimmt. Dieser Umstand verlieh TCP-basiertem Internet-Video-Streaming Auftrieb. Aus diesem Grund konzentriert sich diese Arbeit auf TCP-basiertes Video-Streaming fÃr das Internet. Das Ziel ist es, Video-Streaming in Ãberlasteten und fehlerbehafteten Netzwerken zu verbessern. Die Arbeit umfasst sechs wissenschaftliche BeitrÃ$ge, welche im Folgenden nÃ$her erlÃ$utert werden. (1) Drei adaptive Streaming-Verfahren basierend auf TCP wurden evaluiert, um die LeistungsfÃ$higkeit von TCP-basiertem Streaming unter diversen Netzwerkbedingungen zu bestimmen. Die Ergebnisse dieser Evaluierung dienen als Referenz fÃr weitere Untersuchungen. (2) Untersuchung Ãber den Einfluss von Paketverlust auf die LeistungsfÃ$higkeit von TCP-basiertem Video-Streaming. (3) Ein neues Video-Streaming-Verfahren basierend auf dem Anfrage-Antwort-Prinzip wurde entworfen, u umgehen (die LeistungsfÃ$higkeit von TCP-Streaming verschlechtert sich rapide mit steigendem Paketverlust). Die Neuerung dieses HTTP-basierten Verfahrens ist, dass die Fairness gegenÃber TCP akzeptabel bleibt, obwohl gleichzeitig mehrere DatenstrÃme fÃr die Ébertragung verwendet werden. (4) Ein Modell des HTTP-basierten Anfrage-Antwort Streaming-Verfahrens wurde entwickelt, welches die LeistungsfÃ$higkeit des Verfahrens fÃr unterschiedliche Systemparameter und Netzwerkbedingungen beschreibt. (5) Um die GÃltigkeit des Modells zu bestÃ$tigen, wurde die LeistungsfÃ$higkeit des Anfrage-Antwort-Streaming-Verfahrens unter diversen Netzwerkbedingungen evaluiert. ZusÃ$tzlich wurde die Fairness gegenÃber TCP gemessen. Die Systemparameter des Streaming-Verfahrens kÃnnen so konfiguriert werden, dass Fairness gegenÃber TCP gewÃ$hrleistet werden kann. (6) Ein mobiles Video-Streaming Szenario mit groÃen Bandbreitenschwankungen und RTTs wurde genutzt, um die LeistungsfÃ$higkeit des HTTP-basierten Anfrage-Antwort-Streaming-Verfahrens unter schwierigen Netzwerkbedingungen zu ermitteln. Das Verfahren nutzt die verfÃgbare Bandbreite effizient und kann die Anzahl der QualitÃ$tsÃ$nderungen gering halten. Das HTTP-basierte Anfrage-Antwort-Streaming-Verfahren vereint die gesamte Streaming-Logik im Streaming-Client und schafft es dadurch, die KomplexitÃ$t des Streaming-Verfahrens zu minimieren. ZusÃ$tzlich kann auf Ãnderungen der Netzwerkbedingungen schneller reagiert werden, da der Regelkreis nicht das Netzwerk involviert. Ein weiterer Vorteil von HTTP-basierten AnsÃ$tzen ist die MÃglichkeit, auf vorhandene Infrastruktur (wie z.B. HTTP-Server oder -Proxies) zurÃckzugreifen, um damit die Einsatzkosten zu verringern oder die Skalierbarkeit zu verbessern.Internet video streaming is a hot topic in multimedia systems. A large variety of devices (computers, mobile phones, TVs, etc.) are connected to the Internet via wired or wireless networks and are capable of receiving and decoding HD video content. To enable new services like HD video streaming (e.g., online video rental), the Internet's infrastructure was enhanced. But the Internet is still a best-effort network, which does not implement quality-of-service or admission control, resulting in time-varying bandwidth and packet delay, packet loss and network congestion. Because video streaming accounts for a considerable amount of the Internet's traffic, video streaming needs additionally to be congestion-aware, to avoid a congestion collapse of the Internet. The Transmission Control Protocol (TCP) can adapt to changing network conditions and is currently the de facto standard protocol for congestion-aware and reliable data transmission in the Internet. This fact gave TCP-based video streaming a huge momentum. Consequently, this thesis investigates TCP-based adaptive video streaming for the Internet. The main goal is to provide a solution for congestion-aware video streaming, while still being able to achieve a reasonable performance in error-prone networks. To complement existing work on congestion-aware adaptive streaming, this thesis makes six contributions. (1) The baseline performance of TCP-based adaptive streaming is identified by means of an evaluation of different adaptive streaming approaches. The results represent a reference for further investigations. (2) An investigation on the influence of TCP's behavior in presence of packet loss on the video streaming performance. (3) To overcome the shortcomings of TCP-based video streaming (single TCP connections fail to deliver a good performance in case of packet loss), a new approach to video streaming based on multiple request-response streams was introduced. The novelty of this system is that it is able to make use of multiple HTTP-based request-response streams while still providing TCP-friendliness. (4) A performance model of the HTTP-based request-response streams was developed, to estimate the influence of the system parameters and the network characteristics on the throughput performance. (5) A comprehensive evaluation of the HTTP-based request-response streams under diverse network conditions was conducted, to validate the model's estimations. Additionally, the TCP-friendliness was evaluated, showing that request-response streaming systems can be configured to achieve TCP-friendliness. (6) A cellular network with high bandwidth fluctuations and RTTs was used to investigate the performance of the request-response streaming system in a mobile video streaming scenario. The results indicate that the streaming system can make good use of the available bandwidth, while the number of quality switches is kept low. While aggregating multiple TCP connections to improve the TCP streaming performance is quite common, usually the improvement comes at the cost of high deployment effort. By placing the streaming logic at the client, request-response streams can avoid this complexity. Additionally, this client-driven approach responds faster to changing network conditions and enables easy recovery from connection stalls or aborts, because the control loop is at the client. To improve the network efficiency and the scalability in terms of number of clients served, HTTP-based request-response streams can utilize HTTP proxies and caches.Robert KuschnigAbweichender Titel laut Übersetzung der Verfasserin/des VerfassersZsfassung in dt. SpracheKlagenfurt, Alpen-Adria-Univ., Diss., 2012OeBB(VLID)241068

Secure transport and adaptation of MC-EZBC video utilizing H.264-based transport protocols

AbstractUniversal Multimedia Access (UMA) calls for solutions where content is created once and subsequently adapted to given requirements. With regard to UMA and scalability, which is required often due to a wide variety of end clients, the best suited codecs are wavelet based (like the MC-EZBC) due to their inherent high number of scaling options. However, most transport technologies for delivering videos to end clients are targeted toward the H.264/AVC standard or, if scalability is required, the H.264/SVC. In this paper we will introduce a mapping of the MC-EZBC bitstream to existing H.264/SVC based streaming and scaling protocols. This enables the use of highly scalable wavelet based codecs on the one hand and the utilization of already existing network technologies without accruing high implementation costs on the other hand. Furthermore, we will evaluate different scaling options in order to choose the best option for given requirements. Additionally, we will evaluate different encryption options based on transport and bitstream encryption for use cases where digital rights management is required