Evaluation and optimisation of Less-than-Best-Effort TCP congestion control mechanisms

Increasing use of online software installation, updates, and backup services, as well as the popularity of user-generated content, has increased the demand for band-width in recent years. Traffic generated by these applications — when receiving a ‘fair-share’ of the available bandwidth — can impact the responsiveness of delay-sensitive applications. Less-than-Best-Effort TCP congestion control mechanisms aim to allow lower-priority applications to utilise excess bandwidth with minimum impact to regular TCP carrying delay-sensitive traffic. However, no previous study has evaluated the performance of a large number of this class of congestion con-trol mechanisms. This thesis quantifies the performance of existing Less-than-Best-Effort TCP congestion control mechanisms, and proposes a new mechanism to im-prove the performance of these mechanisms with high path delay. This study first evaluated the performance of seven Less-than-Best-Effort conges-tion control mechanisms in realistic scenarios under a range of network conditions in a Linux testbed incorporating wired Ethernet and 802.11n wireless links. The seven mechanisms evaluated were: Apple LEDBAT, CAIA Delay-Gradient (CDG), RFC6817 LEDBAT, Low Priority, Nice, Westwood-LP, and Vegas. Of these mecha-nisms, only four had existing implementations for modern operating systems. The remaining three mechanisms — Apple LEDBAT, Nice, and Westwood-LP — were implemented based on published descriptions and available code fragments to fa-cilitate this evaluation. The results of the evaluation suggest that Less-than-Best-Effort congestion control mechanisms can be divided into two categories: regular TCP-like mechanisms, and low-impact mechanisms. Of the low-impact mechanisms, two mechanisms were identified as having desirable performance characteristics: Nice and CDG. Nice pro-vides background throughput comparable to regular TCP while maintaining low queuing delay in low path delay settings. CDG has the least impact on regular TCP traffic, at the expense of reduced throughput. In high path-delay settings, these reductions to throughput experienced by CDG are exacerbated, while Nice has a greater impact on regular TCP traffic. To address the very low throughput of existing Less-than-Best-Effort congestion control mechanisms in high path-delay settings, a new Less-than-Best-Effort TCP congestion control algorithm was developed and implemented: Yield TCP. Yield utilises elements of a Proportional-Integral controller to better interpret and re-spond to changes in queuing delay to achieve this goal while also reducing the impact on regular TCP traffic over TCP-like mechanisms. Source code for the im-plementation of Yield developed for this research has also been made available. The results of evaluating Yield indicate that it successfully addresses the low through-put of low-impact Less-than-Best-Effort mechanisms in high delay settings, while also reducing the impact on foreground traffic compared to regular TCP-like con-gestion control mechanisms. Yield also performs similarly to Nice in low delay settings, while also achieving greater intra-protocol fairness than Nice across all settings. These results indicate that Yield addresses the weaknesses of Nice and CDG, and is a promising alternative to existing Less-than-Best-Effort congestion control algorithms

Challenges in Dementia Studies

Alzheimer’s and other neurodegenerative diseases are generally incurable and often difficult to diagnose accurately. Yet early and accurate diagnosis of a neurodegenerative disease can potentially contribute to more effective treatment. Hence research efforts are moving towards early identification of high risk subjects and prevention of disease progression with biomarkers. Unfortunately dementia and biomarker studies are hampered by variables such as drop outs, challenges in comparing data sets, discordant biomarker sets, availability of histopathological confirmation at death, validity of cognitive testing, and nonlinear fluctuations in cognitive domains as disease progresses in vivo in subjects. This chapter is an assessment of the challenges in the early diagnosis of dementia, as well as a presentation of the issues faced in conducting dementia and biomarker studies

National Identity in a Multicultural Nation: The Challenge of Immigration Law and Immigrants

Samuel Huntington\u27s provocative new book Who Are We?: The Challenges to National Identity is rich with insights about the negative impacts of globalization and the burgeoning estrangement of people and businesses in the United States from a truly American identity. The daunting question posed by the title of the book is well worth asking. After commencing the new millennium with wars in Afghanistan and Iraq, U.S. military torture of Iraqi prisoners, indefinite detentions of U.S. citizens declared by the President to be enemy combatants, and a massive domestic war on terror that has punished and frightened Arab, Muslim, and other immigrant communities, many Americans have asked themselves the very same question. Professor Huntington\u27s fear is that the increasingly multicultural United States could disintegrate into the type of ethnic strife that destroyed the former Yugoslavia during the 1990s, or, in less dramatic fashion, divided Quebec for much of the twentieth century. Forming a cohesive national identity with a heterogeneous population is a formidable task but, as Professor Huntington recognizes, critically important to the future of the United States

Entomosporium Leafspot of Photinia and Indian Hawthorn

3 pp., 6 color photosThis leaflet describes the fungus Entomosporium, which attacks photinia and Indian hawthorn plants. The publication describes the disease cycle and recommends cultural practices to control and treat the disease

Chemicals for Plant Disease Control at Home

7 pp., 4 tablesThis publication helps retailers and consumers identify products that control plant diseases. To clear up confusion about the names of the chemicals, the publication cross-references their common names with their chemical terms. It also lists the products commonly available in Texas retail stores and the companies that sell fungicides in small packages for homeowners

An untold leadership story from land of hornbill / Kevin Anak Ong

First and foremost, I would like to convey my heartiest congratulation for TINTA committee for the December 2014 issue publishing. Good job well done to all of you for the hard work presented ever since. Please accept my gratitude for giving me the chance to write a long commentary, lifelong experience in my leadership ever since. As for me, nothing much to be presented, but a true life story of someone that was once born as an ordinary person. Here it goes to the next paragraph

Multiple closed loop recycling of carbon fibre composites with the HiPerDiF (High Performance Discontinuous Fibre) method

AbstractThe aim of this article is to apply the concept of Circular Economy, where end-of-life products and production wastes are recycled into reusable materials, to carbon fibre reinforced plastics. This not only reduces the amount of material disposed into landfills, but also enables manufacturers to achieve significant savings. While current research focuses on the performance of recycled carbon fibre reinforced composites after one recycling process, this paper aims to investigate the performance of composites remanufactured from short carbon fibres that have undergone multiple recycling loops with the High Performance Discontinuous Fibre (HiPerDiF) method. The HiPerDiF method enables the production of aligned short fibre composites with exceptional mechanical properties. In addition, using short fibres makes the composite material intrinsically easy to recycle. Short virgin carbon fibres underwent two loops of fibre reclamation and remanufacturing. A correlation between the composites’ mechanical properties and the nature of the fibres, i.e. reduction in fibre lengths, as well as the residual matrix accumulation from the reclaiming process over a number of recycling loops, was established