Bufferbloat är förekomsten av överdrivet stora buffrar i system för nätverkskommunikation. När TCP-paket fyller buffrarna kommer de inte längre vara användbara och inte längre att ta hand om inkommande/utgående paket vilket leder till fördröjningar. Syftet med denna rapport är att se hur stor påverkan dåligt implementerade buffrar vid flaskhalsar har på latenstiderna i ett nätverk, samt att se hur stor roll en flaskhals har i uppkomsten av bufferbloating. En testmiljö skapades utefter riktlinjer från tidigare forskning och även testerna som utfördes byggdes upp för att efterlikna tidigare forsking. Resultatet av testerna visar att belastningen av nätet inte har påverkat buffertabellen i routingutrustningen nämnvärt, men att flaskhalsen har viss inverkan både på latenstiderna och antalet paket som köats i buffrarna. Men att det inte är ett särskilt akut problem då prestandan över länken inte påverkar märkbart. Inte heller har den ökade belastningen tvingat buffrarna att växa efter konstaterad baseline.

Buffer sizing is an important network configuration parameter that impacts the quality of data traffic. Falling memory cost and the fallacy that ‘more is better’ lead to over provisioning network devices with large buffers. Over-buffering or the so called ‘bufferbloat’ phenomenon creates excessive end-to-end delay in today’s networks. On the other hand, under-buffering results in frequent packet loss and subsequent under-utilization of network resources. The buffer sizing problem has been studied extensively for wired networks. However, there is little work addressing the unique challenges of wireless environment. In this dissertation, we discuss buffer sizing challenges in wireless networks, classify the state-of-the-art solutions, and propose two novel buffer sizing schemes. The first scheme targets buffer sizing in wireless multi-hop networks where the radio spectral resource is shared among a set of con- tending nodes. Hence, it sizes the buffer collectively and distributes it over a set of interfering devices. The second buffer sizing scheme is designed to cope up with recent Wi-Fi enhancements. It adapts the buffer size based on measured link characteristics and network load. Also, it enforces limits on the buffer size to maximize frame aggregation benefits. Both mechanisms are evaluated using simulation as well as testbed implementation over half-duplex and full-duplex wireless networks. Experimental evaluation shows that our proposal reduces latency by an order of magnitude.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-05-31T17:34:37Z No. of bitstreams: 1 thiagoboubeecardozo.pdf: 664105 bytes, checksum: c76b7de470f214d95d3054d0ac7b8232 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-06-01T11:40:26Z (GMT) No. of bitstreams: 1 thiagoboubeecardozo.pdf: 664105 bytes, checksum: c76b7de470f214d95d3054d0ac7b8232 (MD5) / Made available in DSpace on 2017-06-01T11:40:26Z (GMT). No. of bitstreams: 1 thiagoboubeecardozo.pdf: 664105 bytes, checksum: c76b7de470f214d95d3054d0ac7b8232 (MD5) Previous issue date: 2013-05-27 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A Internet é um sistema em contínua evolução. Nesta dissertação, é caracterizada e analisada a recente evolução da conectividade fim-a-fim da Internet, comparando métricas importantes ao desempenho fim-a-fim de dois períodos distintos separados por 5 anos. Os resultados mostram que a distribuição do tamanho médio dos caminhos se mantém pouco alterada de 2006 para 2011, mas a distribuição do atraso acabou piorando, com um aumento de 45% no atraso dos caminhos de 2006 para 2011. Isso afeta diretamente o desempenho e degrada a experiência do usuário. Além disso, é mostrado que a diversidade de caminhos diminuiu e, com isso, os caminhos distintos ficaram um pouco mais similares. Esse resultado tem um impacto direto nos algoritmos de roteamento que tentam explorar a diversidade de caminhos para uma maior tolerância a falhas. Depois foi estudado mais a fundo o fenômeno conhecido como bufferbloat, que é uma das possíveis causas do aparente aumento da latência. Os resultados mostraram que filas muito grandes podem impactar fortemente no desempenho da rede, mas também indicaram que provavelmente o problema não irá ocorrer em máquinas Unix Like com as configurações padrão. / The Internet is a system under continuous evolution. In this dissertation, it is characte rized and analyzed the recent end-to-end connectivity evolution of the Internet, comparing key end-to-end performance metrics from two distinct periods separated by five years. The findings show that the average path length distribution remains virtually unchanged from 2006 to 2011, but the delay distribution actually became worse, with a 45% increase in path delay from 2006 to 2011. This directly affects network performance and degrades user experience. Furthermore, it is shown that path diversity decreased, and accordingly, distinct paths became slightly more similar. This result has a direct impact on routing algorithms that try to explore path diversity to become more fault-tolerant. Later it was studied more deeply the phenomenon known as bufferbloat, which is one of the possible causes of the apparent increase of latency. The results show that large buffers can strongly degrade the network performance, but they also show that the problem is not likely to occur in Unix Like machines with default settings.

Wireless networks are undergoing an unprecedented revolution in the last decade. With the explosion of delay-sensitive applications in the Internet (i.e., online gaming and VoIP), latency becomes a major issue for the development of wireless technology. Taking advantage of the significant decline in memory prices, industrialists equip the network devices with larger buffering capacities to improve the network throughput by limiting packets drops. Over-buffering results in increasing the time that packets spend in the queues and, thus, introducing more latency in networks. This phenomenon is known as “bufferbloat”. While throughput is the dominant performance metric, latency also has a huge impact on user experience not only for real-time applications but also for common applications like web browsing, which is sensitive to latencies in order of hundreds of milliseconds. Concerns have arisen about designing sophisticated queue management schemes to mitigate the effects of such phenomenon. My thesis research aims to solve bufferbloat problem in both traditional half-duplex and cutting-edge full-duplex wireless systems by reducing delay while maximizing wireless links utilization and fairness. Our work shed lights on buffer management algorithms behavior in wireless networks and their ability to reduce latency resulting from excessive queuing delays inside oversized static network buffers without a significant loss in other network metrics. First of all, we address the problem of buffer management in wireless full-duplex networks by using Wireless Queue Management (WQM), which is an active queue management technique for wireless networks. Our solution is based on Relay Full-Duplex MAC (RFD-MAC), an asynchronous media access control protocol designed for relay full-duplexing. Compared to the default case, our solution reduces the end-to-end delay by two orders of magnitude while achieving similar throughput in most of the cases. In the second part of this thesis, we propose a novel design called “LearnQueue” based on reinforcement learning that can effectively control the latency in wireless networks. LearnQueue adapts quickly and intelligently to changes in the wireless environment using a sophisticated reward structure. Testbed results prove that LearnQueue can guarantee low latency while preserving throughput.

As ever more devices are connected to the internet, and applications turn ever more interactive, it becomes more important that the network can be counted on to respond reliably and without unnecessary delay. However, this is far from always the case today, as there can be many potential sources of unnecessary delay. In this thesis we focus on one of them: Excess queueing delay in network routers along the path, also known as bufferbloat. We focus on the home network, and treat the issue in three stages. We examine latency variation and queueing delay on the public internet and show that significant excess delay is often present. Then, we evaluate several modern AQM algorithms and packet schedulers in a residential setting, and show that modern AQMs can almost entirely eliminate bufferbloat and extra queueing latency for wired connections, but that they are not as effective for WiFi links. Finally, we go on to design and implement a solution for bufferbloat at the WiFi link, and also design a workable scheduler-based solution for realising airtime fairness in WiFi. Also included in this thesis is a description of Flent, a measurement tool used to perform most of the experiments in the other papers, and also used widely in the bufferbloat community. / HITS, 4707