5 research outputs found
WE TCP-AP: Wireless Enhanced TCP-AP
Congestion control in wireless networks is strongly dependent on the dynamics and instability of wireless links. It is known that TCP experiences serious performance degradation problems in wireless networks. New approaches based on TCP try to overcome these problems but, although their performance is increased, they incur in congestion control errors, since they do not evaluate accurately the capacity and available link bandwidth in wireless networks. This is also the case of TCP-AP (Adaptive Pacing) that, although presenting clear advantages in wireless networks when compared to other TCP-based approaches, its performance is still lower than rate-based approaches. In this paper we propose a new congestion control protocol based in TCP-AP, the Wireless Enhanced TCP-AP (WE TCPAP).This protocol relies on the MAC layer information gathere by a new method to accurately estimate the available bandwidth and the path capacity over a wireless network path. The new congestion control mechanism is evaluated in different scenarios in wireless mesh and ad-hoc networks, and compared against several approaches for wireless congestion control. It is shown that the new WE TCP-AP outperforms the base TCP-AP, with a more stable behavior and better channel utilization, and its performance gets close to the one of ratebased protocols. This is a very important result, as we show that TCP-based approaches are still able to have good performance in wireless mesh and ad-hoc networks
Simple Yet Efficient, Transparent Airtime Allocation for TCP in Wireless Mesh Networks
In this paper,we explore a simple yet effective technique for explicitly allocating airtime to each active pair of communicating neighbors in a wireless neighborhood so that TCP starvation in a wireless mesh network is avoided. Our explicitallocationisefficient, redistributingunusedairtimeand alsoaccountingforairtimerenderedunusablebyexternal interference. Ourtechniquerequiresnomodificationsto TCP/IP andthe802.11MAC,andisresponsivetoshortflows, MAClayerautorateadaptation,andotherdynamics, as we demonstrate in extensive experiments on two indoor testbeds. Despite its simplicity, the technique is on average within 12% ofthe max-min optimal allocation on several topologies
Congestion Control and Routing over Challenged Networks
This dissertation is a study on the design and analysis of novel, optimal
routing and rate control algorithms in wireless, mobile communication networks.
Congestion control and routing algorithms upto now have been designed and
optimized for wired or wireless mesh networks. In those networks, optimal
algorithms (optimal in the sense that either the throughput is maximized or
delay is minimized, or the network operation cost is minimized) can be
engineered based on the classic time scale decomposition assumption that the
dynamics of the network are either fast enough so that these algorithms
essentially see the average or slow enough that any changes can be tracked to
allow the algorithms to adapt over time. However, as technological advancements
enable integration of ever more mobile nodes into communication networks, any
rate control or routing algorithms based, for example, on averaging out the
capacity of the wireless mobile link or tracking the instantaneous capacity
will perform poorly. The common element in our solution to engineering
efficient routing and rate control algorithms for mobile wireless networks is
to make the wireless mobile links seem as if they are wired or wireless links
to all but few nodes that directly see the mobile links (either the mobiles or
nodes that can transmit to or receive from the mobiles) through an appropriate
use of queuing structures at these selected nodes. This approach allows us to
design end-to-end rate control or routing algorithms for wireless mobile
networks so that neither averaging nor instantaneous tracking is necessary
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