273 research outputs found
Optimization flow control -- I: Basic algorithm and convergence
We propose an optimization approach to flow control where the objective is to maximize the aggregate source utility over their transmission rates. We view network links and sources as processors of a distributed computation system to solve the dual problem using a gradient projection algorithm. In this system, sources select transmission rates that maximize their own benefits, utility minus bandwidth cost, and network links adjust bandwidth prices to coordinate the sources' decisions. We allow feedback delays to be different, substantial, and time varying, and links and sources to update at different times and with different frequencies. We provide asynchronous distributed algorithms and prove their convergence in a static environment. We present measurements obtained from a preliminary prototype to illustrate the convergence of the algorithm in a slowly time-varying environment. We discuss its fairness property
Distributed Rate Allocation Policies for Multi-Homed Video Streaming over Heterogeneous Access Networks
We consider the problem of rate allocation among multiple simultaneous video
streams sharing multiple heterogeneous access networks. We develop and evaluate
an analytical framework for optimal rate allocation based on observed available
bit rate (ABR) and round-trip time (RTT) over each access network and video
distortion-rate (DR) characteristics. The rate allocation is formulated as a
convex optimization problem that minimizes the total expected distortion of all
video streams. We present a distributed approximation of its solution and
compare its performance against H-infinity optimal control and two heuristic
schemes based on TCP-style additive-increase-multiplicative decrease (AIMD)
principles. The various rate allocation schemes are evaluated in simulations of
multiple high-definition (HD) video streams sharing multiple access networks.
Our results demonstrate that, in comparison with heuristic AIMD-based schemes,
both media-aware allocation and H-infinity optimal control benefit from
proactive congestion avoidance and reduce the average packet loss rate from 45%
to below 2%. Improvement in average received video quality ranges between 1.5
to 10.7 dB in PSNR for various background traffic loads and video playout
deadlines. Media-aware allocation further exploits its knowledge of the video
DR characteristics to achieve a more balanced video quality among all streams.Comment: 12 pages, 22 figure
Simulation comparison of RED and REM
We propose earlier an optimization based low control for the Internet called Random Exponential Marking (REM). REM consists of a link algorithm, that probabilistically marks packets inside the network, and a source algorithm, that adapts source rate to observed marking. The marking probability is exponential in a link congestion measure, so that the end-to-end marking probability is exponential in a path congestion measure. Because of the finer measure of congestion provided by REM, sources do not constantly probe the network for spare capacity, but settle around a globally optimal equilibrium, thus avoiding the perpetual cycle of sinking into and recovering from congestion. In this paper we compare the performance of REM with Reno over RED through simulation
Optimization flow control with Newton-like algorithm
We proposed earlier an optimization approach to reactive flow control where the objective of the control is to maximize the aggregate utility of all sources over their transmission rates. The control mechanism is derived as a gradient projection algorithm to solve the dual problem. In this paper we extend the algorithm to a scaled gradient projection. The diagonal scaling matrix approximates the diagonal terms of the Hessian and can be computed at individual links using the same information required by the unscaled algorithm. We prove the convergence of the scaled algorithm and present simulation results that illustrate its superiority to the unscaled algorithm
Satellite ATM Network Architectural Considerations and TCP/IP Performance
In this paper, we have provided a summary of the design options in
Satellite-ATM technology. A satellite ATM network consists of a space segment
of satellites connected by inter-satellite crosslinks, and a ground segment of
the various ATM networks. A satellite-ATM interface module connects the
satellite network to the ATM networks and performs various call and control
functions. A network control center performs various network management and
resource allocation functions. Several issues such as the ATM service model,
media access protocols, and traffic management issues must be considered when
designing a satellite ATM network to effectively transport Internet traffic. We
have presented the buffer requirements for TCP/IP traffic over ATM-UBR for
satellite latencies. Our results are based on TCP with selective
acknowledgments and a per-VC buffer management policy at the switches. A buffer
size of about 0.5 * RTT to 1 * RTT is sufficient to provide over 98% throughput
to infinite TCP traffic for long latency networks and a large number of
sources. This buffer requirement is independent of the number of sources. The
fairness is high for a large numbers of sources because of the per-VC buffer
management performed at the switches and the nature of TCP traffic.Comment: Proceedings of the 3rd Ka Band Utilization Converence, Italy, 1997,
pp481-48
Satellite Networks: Architectures, Applications, and Technologies
Since global satellite networks are moving to the forefront in enhancing the national and global information infrastructures due to communication satellites' unique networking characteristics, a workshop was organized to assess the progress made to date and chart the future. This workshop provided the forum to assess the current state-of-the-art, identify key issues, and highlight the emerging trends in the next-generation architectures, data protocol development, communication interoperability, and applications. Presentations on overview, state-of-the-art in research, development, deployment and applications and future trends on satellite networks are assembled
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The Impact of Multicast Layering on Network Fairness
Many definitions of fairness for multicast networks assume that sessions are single-rate, requiring that each multicast session trans- mits data to all of its receivers at the same rate. These defini- tions do not account for multi-rate approaches, such as layering, that permit receiving rates within a session to be chosen indepen- dently. We identify four desirable fairness properties for multicast networks, derived from properties that hold within the max-min fair allocations of unicast networks. We extend the definition of multicast max-min fairness to networks that contain multi-rate sessions, and show that all four fairness properties hold in a multi- rate max-min fair allocation, but need not hold in a single-rate max-min fair allocation. We then show that multi-rate max-min fair rate allocations can be achieved via intra-session coordinated joins and leaves of multicast groups. However, in the absence of coordination, the resulting max-min fair rate allocation uses link bandwidth inefficiently, and does not exhibit some of the desir- able fairness properties. We evaluate this inefficiency for several layered multi-rate congestion control schemes, and find that, in a protocol where the sender coordinates joins, this inefficiency has minimal impact on desirable fairness properties. Our results indicate that sender-coordinated layered protocols show promise for achieving desirable fairness properties for allocations in large- scale multicast networks
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 nĂŁo Ă© 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 disponĂvel. Assim, Ă©
importante para melhorar o desempenho do controlo de congestionamento
em redes sem fios, incluir componentes que sĂŁo 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 disponĂvel entre mĂşltiplas aplicações concorrentes Ă©
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 disponĂvel 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 disponĂvel, 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 disponĂvel 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
Ăsticas novas para melhorar o seu desempenho, de entre as quais
se destaca a utilização da informação de largura de banda disponĂvel
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
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