25 research outputs found
Networking Mechanisms for Delay-Sensitive Applications
The diversity of applications served by the explosively growing Internet is increasing. In particular, applications that are sensitive to end-to-end packet delays become more common and include telephony, video conferencing, and networked games. While the single best-effort service of the current Internet favors throughput-greedy traffic by equipping congested links with large buffers, long queuing at the congested links hurts the delay-sensitive applications. Furthermore, while numerous alternative architectures have been proposed to offer diverse network services, the innovative alternatives failed to gain widespread end-to-end deployment. This dissertation explores different networking mechanisms for supporting low queueing delay required by delay-sensitive applications. In particular, it considers two different approaches. The first one assumes employing congestion control protocols for the traffic generated by the considered class of applications. The second approach relies on the router operation only and does not require support from end hosts
Reducing Internet Latency : A Survey of Techniques and their Merit
Bob Briscoe, Anna Brunstrom, Andreas Petlund, David Hayes, David Ros, Ing-Jyh Tsang, Stein Gjessing, Gorry Fairhurst, Carsten Griwodz, Michael WelzlPeer reviewedPreprin
Examination of air transportation trip time variability
Scheduled air transportation is required to provide a service that is safe, consistent, and dependable, with reliable trip times and delays managed within acceptable limits. High trip time variability and delay in the current system are driven by multiple factors; The study objectives were: (1) to develop a comprehensive database for individual major U.S. airline domestic trips between 1995 and 2005; (2) to explore the central tendency and variability of airline gate-to-gate trip times and delays; (3) to develop values for unconstrained, or unimpeded, trip times, and (4) to develop traveler and airline delay and variability costs relative to unimpeded trip times; The research used U.S. Department of Transportation (U.S. DOT) data for scheduled domestic airline trips reported by major U.S. air carriers between 1995 and 2005. For valuing air carrier cost savings, this research estimated variable costs for individual trips, based on individual carrier financial reports to U.S. DOT; The research used reported trip times as a primary indicator, unimpeded trip times as a reference, and attached a cost to the excess of reported trip time over unimpeded trip time at the individual flight level. This approach represents a process for evaluating the time savings and operating cost impacts of measures for increasing capacity and reducing impedance in U.S. domestic scheduled air transportation; Areas in which trip time variability and delay impose a high penalty on travelers and airlines were identified. The most important study results concerned disproportionately higher delays and costs relative to: (1) origin and destination airports and corridors; (2) times of day; and (3) the days with highest delays. The main areas were arrivals and departures at leading airports (40 percent of flights and 55 percent of costs), flight departures and arrivals between noon and early evening (50 percent of flights and 60 percent of costs), and during the 40 percent of days in which there were heavy system wide delays (55 percent of costs) costs appropriate to time changes on individual trips, the magnitude of penalties incurred by impeded trips were estimated relative to unimpeded trips. These were: 150 million annual excess traveler hours per year; {dollar}8 billion annual excess air carrier operating costs; with 400 million annual gallons of excess jet fuel consumption. The costs of impeded trips added about 10 percent (or about {dollar}3.4 billion annually) to airline variable operating costs during the study period
Controlo de congestionamento em redes sem fios
Doutoramento em Engenharia ElectrotécnicaCongestion control in wireless networks is an important and open issue.
Previous research has proven the poor performance of the Transport
Control Protocol (TCP) in such networks. The factors that contribute
to the poor performance of TCP in wireless environments concern its
unsuitability to identify/detect and react properly to network events,
its TCP window based
ow control algorithm that is not suitable for
the wireless channel, and the congestion collapse due to mobility. New
rate based mechanisms have been proposed to mitigate TCP performance
in wired and wireless networks. However, these mechanisms
also present poor performance, as they lack of suitable bandwidth estimation
techniques for multi-hop wireless networks.
It is thus important to improve congestion control performance in wireless
networks, incorporating components that are suitable for wireless
environments. A congestion control scheme which provides an e -
cient and fair sharing of the underlying network capacity and available
bandwidth among multiple competing applications is crucial to the definition
of new e cient and fair congestion control schemes on wireless
multi-hop networks.
The Thesis is divided in three parts. First, we present a performance
evaluation study of several congestion control protocols against TCP,
in wireless mesh and ad-hoc networks. The obtained results show that
rate based congestion control protocols need an eficient and accurate
underlying available bandwidth estimation technique. The second part
of the Thesis presents a new link capacity and available bandwidth estimation
mechanism denoted as rt-Winf (real time wireless inference).
The estimation is performed in real-time and without the need to intrusively
inject packets in the network. Simulation results show that
rt-Winf obtains the available bandwidth and capacity estimation with
accuracy and without introducing overhead trafic in the network.
The third part of the Thesis proposes the development of new congestion
control mechanisms to address the congestion control problems
of wireless networks. These congestion control mechanisms use cross
layer information, obtained by rt-Winf, to accurately and eficiently estimate
the available bandwidth and the path capacity over a wireless
network path. Evaluation of these new proposed mechanisms, through
ns-2 simulations, shows that the cooperation between rt-Winf and the
congestion control algorithms is able to significantly increase congestion
control eficiency and network performance.O controlo de congestionamento continua a ser extremamente importante
quando se investiga o desempenho das redes sem fios. Trabalhos
anteriores mostram o mau desempenho do Transport Control Proto-
col (TCP) em redes sem fios. Os fatores que contribuem para um
pior desempenho do TCP nesse tipo de redes s~ao: a sua falta de capacidade
para identificar/detetar e reagir adequadamente a eventos da
rede; a utilização de um algoritmo de controlo de
uxo que não é adequado
para o canal sem fios; e o colapso de congestionamento devido
á mobilidade. Para colmatar este problemas foram propostos novos
mecanismos de controlo de congestionamento baseados na taxa de
transmissão. No entanto, estes mecanismos também apresentam um
pior desempenho em redes sem fios, já que não utilizam mecanismos
adequados para a avaliação da largura de banda disponível. Assim, é
importante para melhorar o desempenho do controlo de congestionamento
em redes sem fios, incluir componentes que são adequados para
esse tipo de ambientes. Um esquema de controlo de congestionamento
que permita uma partilha eficiente e justa da capacidade da rede e da
largura de banda disponível entre múltiplas aplicações concorrentes é
crucial para a definição de novos, eficientes e justos mecanismos de
controlo congestionamento para as redes sem fios.
A Tese está dividida em três partes. Primeiro, apresentamos um estudo
sobre a avaliação de desempenho de vários protocolos de controlo de
congestionamento relativamente ao TCP, em redes sem fios em malha
e ad-hoc. Os resultados obtidos mostram que os protocolos baseados
na taxa de transmissão precisam de uma técnica de avaliação da largura
de banda disponível que seja eficiente e precisa . A segunda parte da
Tese apresenta um novo mecanismo de avaliação da capacidade da
ligação e da largura de banda disponível, designada por rt-Winf (real
time wireless inference). A avaliação é realizada em tempo real e sem
a necessidade de inserir tráfego na rede. Os resultados obtidos através
de simulação e emulação mostram que o rt-Winf obtém com precisão
a largura de banda disponível e a capacidade da ligação sem sobrecarregar
a rede. A terceira parte da Tese propõe novos mecanismos de
controlo de congestionamento em redes sem fios. Estes mecanismos
de controlo de congestionamento apresentam um conjunto de caracter
ísticas novas para melhorar o seu desempenho, de entre as quais
se destaca a utilização da informação de largura de banda disponível
obtida pelo rt-Winf. Os resultados da avaliação destes mecanismos,
utilizando o simulador ns-2, permitem concluir que a cooperação entre
o rt-Winf e os algoritmos de controlo de congestionamento aumenta
significativamente o desempenho da rede
Actas da 10ª Conferência sobre Redes de Computadores
Universidade do MinhoCCTCCentro AlgoritmiCisco SystemsIEEE Portugal Sectio
Re-feedback: freedom with accountability for causing congestion in a connectionless internetwork
This dissertation concerns adding resource accountability to a simplex internetwork such as the Internet,
with only necessary but sufficient constraint on freedom. That is, both freedom for applications to evolve
new innovative behaviours while still responding responsibly to congestion; and freedom for network
providers to structure their pricing in any way, including flat pricing.
The big idea on which the research is built is a novel feedback arrangement termed ‘re-feedback’.
A general form is defined, as well as a specific proposal (re-ECN) to alter the Internet protocol so that
self-contained datagrams carry a metric of expected downstream congestion.
Congestion is chosen because of its central economic role as the marginal cost of network usage.
The aim is to ensure Internet resource allocation can be controlled either by local policies or by market
selection (or indeed local lack of any control).
The current Internet architecture is designed to only reveal path congestion to end-points, not networks.
The collective actions of self-interested consumers and providers should drive Internet resource
allocations towards maximisation of total social welfare. But without visibility of a cost-metric, network
operators are violating the architecture to improve their customer’s experience. The resulting fight
against the architecture is destroying the Internet’s simplicity and ability to evolve.
Although accountability with freedom is the goal, the focus is the congestion metric, and whether
an incentive system is possible that assures its integrity as it is passed between parties around the system,
despite proposed attacks motivated by self-interest and malice.
This dissertation defines the protocol and canonical examples of accountability mechanisms. Designs
are all derived from carefully motivated principles. The resulting system is evaluated by analysis
and simulation against the constraints and principles originally set. The mechanisms are proven to be
agnostic to specific transport behaviours, but they could not be made flow-ID-oblivious
Enhancing programmability for adaptive resource management in next generation data centre networks
Recently, Data Centre (DC) infrastructures have been growing rapidly to support a wide range of emerging services, and provide the underlying connectivity and compute resources that facilitate the "*-as-a-Service" model. This has led to the deployment of a multitude of services multiplexed over few, very large-scale centralised infrastructures. In order to cope with the ebb and flow of users, services and traffic, infrastructures have been provisioned for peak-demand resulting in the average utilisation of resources to be low. This overprovisionning has been further motivated by the complexity in predicting traffic demands over diverse timescales and the stringent economic impact of outages. At the same time, the emergence of Software Defined Networking (SDN), is offering new means to monitor and manage the network infrastructure to address this underutilisation.
This dissertation aims to show how measurement-based resource management can improve performance and resource utilisation by adaptively tuning the infrastructure to the changing operating conditions. To achieve this dynamicity, the infrastructure must be able to centrally monitor, notify and react based on the current operating state, from per-packet dynamics to longstanding traffic trends and topological changes. However, the management and orchestration abilities of current SDN realisations is too limiting and must evolve for next generation networks. The current focus has been on logically centralising the routing and forwarding decisions. However, in order to achieve the necessary fine-grained insight, the data plane of the individual device must be programmable to collect and disseminate the metrics of interest.
The results of this work demonstrates that a logically centralised controller can dynamically collect and measure network operating metrics to subsequently compute and disseminate fine-tuned environment-specific settings. They show how this approach can prevent TCP throughput incast collapse and improve TCP performance by an order of magnitude for partition-aggregate traffic patterns. Futhermore, the paradigm is generalised to show the benefits for other services widely used in DCs such as, e.g, routing, telemetry, and security