A genetic approach to Markovian characterisation of H.264 scalable video

We propose an algorithm for multivariate Markovian characterisation of H.264/SVC scalable video traces at the sub-GoP (Group of Pictures) level. A genetic algorithm yields Markov models with limited state space that accurately capture temporal and inter-layer correlation. Key to our approach is the covariance-based fitness function. In comparison with the classical Expectation Maximisation algorithm, ours is capable of matching the second order statistics more accurately at the cost of less accuracy in matching the histograms of the trace. Moreover, a simulation study shows that our approach outperforms Expectation Maximisation in predicting performance of video streaming in various networking scenarios

Statistical Analysis of Video Frame Size Distribution Originating from Scalable Video Codec (SVC)

Designing an effective and high performance network requires an accurate characterization and modeling of network traffic.The modeling of video frame sizes is normally applied in simulation studies and mathematical analysis and generating streams for testing and compliance purposes. Besides, video traffic assumed as a major source of multimedia traffic in future heterogeneous network. Therefore, the statistical distribution of video data can be used as the inputs for performance modeling of networks. The finding of this paper comprises the theoretical definition of distribution which seems to be relevant to the video trace in terms of its statistical properties and finds the best distribution using both the graphical method and the hypothesis test.The data set used in this article consists of layered video traces generating from Scalable Video Codec (SVC) video compression technique of three different movies

Quantifying the impact of daily and seasonal variation in sap pH on xylem dissolved inorganic carbon estimates in plum trees

In studies on internal CO2 transport, average xylem sap pH (pH(x)) is one of the factors used for calculation of the concentration of dissolved inorganic carbon in the xylem sap ([CO2*]). Lack of detailed pH(x) measurements at high temporal resolution could be a potential source of error when evaluating [CO2*] dynamics. In this experiment, we performed continuous measurements of CO2 concentration ([CO2]) and stem temperature (T-stem), complemented with pH(x) measurements at 30-min intervals during the day at various stages of the growing season (Day of the Year (DOY): 86 (late winter), 128 (mid-spring) and 155 (early summer)) on a plum tree (Prunus domestica L. cv. Reine Claude d'Oullins). We used the recorded pH(x) to calculate [CO2*] based on T-stem and the corresponding measured [CO2]. No statistically significant difference was found between mean [CO2*] calculated with instantaneous pH(x) and daily average pH(x). However, using an average pH(x) value from a different part of the growing season than the measurements of [CO2] and T-stem to estimate [CO2*] led to a statistically significant error. The error varied between 3.25 +/- 0.01% under-estimation and 3.97 * 0.01% over-estimation, relative to the true [CO2*] data. Measured pH(x) did not show a significant daily variation, unlike [CO2], which increased during the day and declined at night. As the growing season progressed, daily average [CO2] (3.4%, 5.3%, 7.4%) increased and average pH(x) (5.43, 5.29, 5.20) decreased. Increase in [CO2] will increase its solubility in xylem sap according to Henry's law, and the dissociation of [CO2*] will negatively affect pH(x). Our results are the first quantifying the error in [CO2*] due to the interaction between [CO2] and pH(x) on a seasonal time scale. We found significant changes in pH(x) across the growing season, but overall the effect on the calculation of [CO2*] remained within an error range of 4%. However, it is possible that the error could be more substantial for other tree species, particularly if pH(x) is in the more sensitive range (pHx > 6.5)

Análisis de tráfico multicast de video H264/Theora en redes Wi-Fi IEEE 802.11ac

En los últimos años el tráfico de video ha crecido en forma exponencial, especialmente en los dispositivos móviles. Conocer el comportamiento del mismo y los requisitos necesarios de la red, ayudan a los administradores de la red a una mejor implementación. En este trabajo se propone un experimento de tráfico de video multicast en una red de laboratorio real como test bed. Se usa una topología en redes cableadas e inalámbricas con clientes inalámbricos trabajando en la norma IEEE 802.11ac. El tráfico de video se codificará en H264 y Theora, para evaluar y comprender el impacto sobre el tráfico de la red. Se analizará midiendo y comparando distintas métricas como cantidad de paquetes y bytes, espacios intertramas, tamaños de paquetes y tasa de bits efectiva para cada tipo de códec, etc. Además, se plantea un análisis estadístico de distribución de tramas. Este trabajo es una continuación de experimentaciones realizadas sobre redes cableadas para tráfico de video con codecs H261, H263 y H264. Las conclusiones del trabajo ayudarán a determinar las configuraciones a tener en cuenta para una adecuada gestión de redes similares y un uso eficiente de los recursos disponibles, sin comprometer el rendimiento y la QoS esperada.Eje: Arquitectura, Redes y Sistemas Operativos.Red de Universidades con Carreras en Informática (RedUNCI

Exploration and Design of Power-Efficient Networked Many-Core Systems

Multiprocessing is a promising solution to meet the requirements of near future applications. To get full benefit from parallel processing, a manycore system needs efficient, on-chip communication architecture. Networkon- Chip (NoC) is a general purpose communication concept that offers highthroughput, reduced power consumption, and keeps complexity in check by a regular composition of basic building blocks. This thesis presents power efficient communication approaches for networked many-core systems. We address a range of issues being important for designing power-efficient manycore systems at two different levels: the network-level and the router-level. From the network-level point of view, exploiting state-of-the-art concepts such as Globally Asynchronous Locally Synchronous (GALS), Voltage/ Frequency Island (VFI), and 3D Networks-on-Chip approaches may be a solution to the excessive power consumption demanded by today’s and future many-core systems. To this end, a low-cost 3D NoC architecture, based on high-speed GALS-based vertical channels, is proposed to mitigate high peak temperatures, power densities, and area footprints of vertical interconnects in 3D ICs. To further exploit the beneficial feature of a negligible inter-layer distance of 3D ICs, we propose a novel hybridization scheme for inter-layer communication. In addition, an efficient adaptive routing algorithm is presented which enables congestion-aware and reliable communication for the hybridized NoC architecture. An integrated monitoring and management platform on top of this architecture is also developed in order to implement more scalable power optimization techniques. From the router-level perspective, four design styles for implementing power-efficient reconfigurable interfaces in VFI-based NoC systems are proposed. To enhance the utilization of virtual channel buffers and to manage their power consumption, a partial virtual channel sharing method for NoC routers is devised and implemented. Extensive experiments with synthetic and real benchmarks show significant power savings and mitigated hotspots with similar performance compared to latest NoC architectures. The thesis concludes that careful codesigned elements from different network levels enable considerable power savings for many-core systems.Siirretty Doriast

Análisis de tráfico multicast de video H264/Theora en redes Wi-Fi IEEE 802.11ac

En los últimos años el tráfico de video ha crecido en forma exponencial, especialmente en los dispositivos móviles. Conocer el comportamiento del mismo y los requisitos necesarios de la red, ayudan a los administradores de la red a una mejor implementación. En este trabajo se propone un experimento de tráfico de video multicast en una red de laboratorio real como test bed. Se usa una topología en redes cableadas e inalámbricas con clientes inalámbricos trabajando en la norma IEEE 802.11ac. El tráfico de video se codificará en H264 y Theora, para evaluar y comprender el impacto sobre el tráfico de la red. Se analizará midiendo y comparando distintas métricas como cantidad de paquetes y bytes, espacios intertramas, tamaños de paquetes y tasa de bits efectiva para cada tipo de códec, etc. Además, se plantea un análisis estadístico de distribución de tramas. Este trabajo es una continuación de experimentaciones realizadas sobre redes cableadas para tráfico de video con codecs H261, H263 y H264. Las conclusiones del trabajo ayudarán a determinar las configuraciones a tener en cuenta para una adecuada gestión de redes similares y un uso eficiente de los recursos disponibles, sin comprometer el rendimiento y la QoS esperada.Eje: Arquitectura, Redes y Sistemas Operativos.Red de Universidades con Carreras en Informática (RedUNCI

Analysis and modelling of traffic produced by adaptive HTTP-based video

The increase of HTTP-based video popularity causes that broadband and Internet service providers' links transmit mainly multimedia content. Network planning, traffic engineering or congestion control requires an understanding of the statistical properties of network traffic; therefore, it is desirable to investigate the characteristic of traffic traces generated by systems which employ adaptive bit-rate streaming. Our first contribution is an investigation of traffic originating from 120 client-server pairs, situated in an emulated content distribution network, and multiplexed onto a single network link. We show that the structure of the traffic is distinct from the structure generated by the first and second generation of HTTP video systems, and furthermore, not similar to the structure of general Internet traffic. The obtained traffic exhibits negative and positive correlations, anti-persistence, and its distribution function is skewed to the right. Our second contribution is an approximation of the traffic by ARIMA/FARIMA processes blue and artificial neural networks. As we show, the obtained traffic models are able to enhance the performance of an adaptive streaming algorithm. Document type: Articl

Portable Video Streaming Network

This dissertation addresses the challenge of developing a video call system capable of supporting both Android mobile devices and fixed computers. Addi tionally, it analyses the quality of video achieved and its variation in the presence of network bandwidth and packet loss constraints. A prototype of a video call system was implemented using a web application and the Web Real-Time Communication (WebRTC) library. Clients use WebRTC to stream video over a Traversal Using Relays around NAT (TURN) relay server, allowing them to send video to any terminal connected to the Internet. Signalling was implemented using WebSockets and a Node.js server. A quality testing prototype was also implemented, which supports sending pre-recorded videos and capturing and storing video recordings at the sender and receiver. The Video Multimethod Assessment Fusion (VMAF) metric was used as the main video quality metric, based on the comparison between the transmitted and received videos. The quality of a video encoded using the open source video encoder VP8 was analysed in constrained network setups. The results measured the video quality degradation and percentage of received frames, showing that the system is resilient to some bandwidth strangulation and packet loss, although with a noticeable video quality degradation.Esta dissertação aborda o desafio de desenvolver um sistema de videochamada capaz de suportar dispositivos móveis Android e computadores fixos. Além disso, analisa a qualidade do vídeo obtida e sua variação na presença de restrições de largura de banda da rede e perda de pacotes. Um protótipo de um sistema de videochamada foi implementado usando uma aplicação web e a biblioteca Web Real-Time Communication (WebRTC). Os clientes usam WebRTC para transmitir o vídeo através de um servidor de retransmissão Traversal Using Relays around NAT (TURN), permitindo que enviem vídeo a qualquer cliente ligado à Internet. A sinalização foi implementada usando WebSockets e um servidor Node.js. Também foi implementado um protótipo de teste de qualidade, que suporta o envio de vídeos pré-gravados e a captura e armazenamento de gravações de vídeo no emissor e no recetor. A métrica Video Multimethod Assessment Fusion (VMAF) foi utilizada como a principal métrica de qualidade de vídeo, com base na comparação entre os vídeos transmitidos e recebidos. A qualidade de um vídeo codificado usando VP8 foi analisada em configurações de rede com limitações. Os resultados mediram a degradação da qualidade do vídeo e a percentagem de tramas recebidas, mostrando que o sistema é resiliente a algum estrangulamento da largura de banda e perda de pacotes, embora com uma degradação percetível da qualidade do vídeo