140 research outputs found
Comparative Study on the Performance of TCP-Freeze and TCP-Newreno Over Divert Failure Routing Protocol
Many enhancements have been proposed to address TCP throughput issues over wireless links. In this project, we will study the performance of the standard TCP over TCP Freeze with Divert Route Failure Protocol as the routing mechanism. This study is aimed for the purpose of further improvement in related services provided by TCP over the wireless links. Such enhancements are needed due to the high transmission error rates in wireless links
TCP performance enhancement in wireless networks via adaptive congestion control and active queue management
The transmission control protocol (TCP) exhibits poor performance when used in error-prone wireless networks. Remedy to this problem has been an active research area. However, a widely accepted and adopted solution is yet to emerge. Difficulties of an acceptable solution lie in the areas of compatibility, scalability, computational complexity and the involvement of intermediate routers and switches.
This dissertation rexriews the current start-of-the-art solutions to TCP performance enhancement, and pursues an end-to-end solution framework to the problem. The most noticeable cause of the performance degradation of TCP in wireless networks is the higher packet loss rate as compared to that in traditional wired networks. Packet loss type differentiation has been the focus of many proposed TCP performance enhancement schemes. Studies conduced by this dissertation research suggest that besides the standard TCP\u27s inability of discriminating congestion packet losses from losses related to wireless link errors, the standard TCP\u27s additive increase and multiplicative decrease (AIMD) congestion control algorithm itself needs to be redesigned to achieve better performance in wireless, and particularly, high-speed wireless networks. This dissertation proposes a simple, efficient, and effective end-to-end solution framework that enhances TCP\u27s performance through techniques of adaptive congestion control and active queue management. By end-to-end, it means a solution with no requirement of routers being wireless-aware or wireless-specific .
TCP-Jersey has been introduced as an implementation of the proposed solution framework, and its performance metrics have been evaluated through extensive simulations. TCP-Jersey consists of an adaptive congestion control algorithm at the source by means of the source\u27s achievable rate estimation (ARE) —an adaptive filter of packet inter-arrival times, a congestion indication algorithm at the links (i.e., AQM) by means of packet marking, and a effective loss differentiation algorithm at the source by careful examination of the congestion marks carried by the duplicate acknowledgment packets (DUPACK).
Several improvements to the proposed TCP-Jersey have been investigated, including a more robust ARE algorithm, a less computationally intensive threshold marking algorithm as the AQM link algorithm, a more stable congestion indication function based on virtual capacity at the link, and performance results have been presented and analyzed via extensive simulations of various network configurations. Stability analysis of the proposed ARE-based additive increase and adaptive decrease (AJAD) congestion control algorithm has been conducted and the analytical results have been verified by simulations. Performance of TCP-Jersey has been compared to that of a perfect , but not practical, TCP scheme, and encouraging results have been observed. Finally the framework of the TCP-Jersey\u27s source algorithm has been extended and generalized for rate-based congestion control, as opposed to TCP\u27s window-based congestion control, to provide a design platform for applications, such as real-time multimedia, that do not use TCP as transport protocol yet do need to control network congestion as well as combat packet losses in wireless networks.
In conclusion, the framework architecture presented in this dissertation that combines the adaptive congestion control and active queue management in solving the TCP performance degradation problem in wireless networks has been shown as a promising answer to the problem due to its simplistic design philosophy complete compatibility with the current TCP/IP and AQM practice, end-to-end architecture for scalability, and the high effectiveness and low computational overhead. The proposed implementation of the solution framework, namely TCP-Jersey is a modification of the standard TCP protocol rather than a completely new design of the transport protocol. It is an end-to-end approach to address the performance degradation problem since it does not require split mode connection establishment and maintenance using special wireless-aware software agents at the routers. The proposed solution also differs from other solutions that rely on the link layer error notifications for packet loss differentiation.
The proposed solution is also unique among other proposed end-to-end solutions in that it differentiates packet losses attributed to wireless link errors from congestion induced packet losses directly from the explicit congestion indication marks in the DUPACK packets, rather than inferring the loss type based on packet delay or delay jitter as in many other proposed solutions; nor by undergoing a computationally expensive off-line training of a classification model (e.g., HMM), or a Bayesian estimation/detection process that requires estimations of a priori loss probability distributions of different loss types.
The proposed solution is also scalable and fully compatible to the current practice in Internet congestion control and queue management, but with an additional function of loss type differentiation that effectively enhances TCP\u27s performance over error-prone wireless networks.
Limitations of the proposed solution architecture and areas for future researches are also addressed
Web browsing optimization over 2.5G and 3G: end-to-end mechanisms vs. usage of performance enhancing proxies
Published version on Wiley's platform: https://onlinelibrary.wiley.com/doi/abs/10.1002/wcm.4562.5 Generation (2.5G) and Third Generation (3G) cellular wireless networks allow mobile Internet access withbearers specifically designed for data communications. However, Internet protocols under-utilize wireless widearea network (WWAN) link resources, mainly due to large round trip times (RTTs) and request–reply protocolpatterns. Web browsing is a popular service that suffers significant performance degradation over 2.5G and 3G. Inthis paper, we review and compare the two main approaches for improving web browsing performance over wirelesslinks: (i) using adequate end-to-end parameters and mechanisms and (ii) interposing a performance enhancingproxy (PEP) between the wireless and wired parts. We conclude that PEPs are currently the only feasible way forsignificantly optimizing web browsing behavior over 2.5G and 3G. In addition, we evaluate the two main currentcommercial PEPs over live general packet radio service (GPRS) and universal mobile telecommunications system(UMTS) networks. The results show that PEPs can lead to near-ideal web browsing performance in certain scenarios.Postprint (published version
MANETs: Internet Connectivity and Transport Protocols
A Mobile Ad hoc Network (MANET) is a collection of mobile nodes connected together over a wireless medium, which self-organize into an autonomous multi-hop wireless network. This kind of networks allows people and devices to seamlessly internetwork in areas with no pre-existing communication infrastructure, e.g., disaster recovery environments. Ad hoc networking is not a new concept, having been around in various forms for over 20 years. However, in the past only tactical networks followed the ad hoc networking paradigm. Recently, the introduction of new technologies such as IEEE 802.11, are moved the application field of MANETs to a more commercial field. These evolutions have been generating a renewed and growing interest in the research and development of MANETs.
It is widely recognized that a prerequisite for the commercial penetration of the ad hoc networking technologies is the integration with existing wired/wireless infrastructure-based networks to provide an easy and transparent access to the Internet and its services. However, most of the existing solutions for enabling the interconnection between MANETs and the Internet are based on complex and inefficient mechanisms, as Mobile-IP and IP tunnelling. This thesis describes an alternative approach to build multi-hop and heterogeneous proactive ad hoc networks, which can be used as flexible and low-cost extensions of traditional wired LANs. The proposed architecture provides transparent global Internet connectivity and address autocofiguration capabilities to mobile nodes without requiring configuration changes in the pre-existing wired LAN, and relying on basic layer-2 functionalities. This thesis also includes an experimental evaluation of the proposed architecture and a comparison between this architecture with a well-known alternative NAT-based solution. The experimental outcomes confirm that the proposed technique ensures higher per-connection throughputs than the NAT-based solution.
This thesis also examines the problems encountered by TCP over multi-hop ad hoc networks. Research on efficient transport protocols for ad hoc networks is one of the most active topics in the MANET community. Such a great interest is basically motivated by numerous observations showing that, in general, TCP is not able to efficiently deal with the unstable and very dynamic environment provided by multi-hop ad hoc networks. This is because some assumptions, in TCP design, are clearly inspired by the characteristics of wired networks dominant at the time when it was conceived. More specifically, TCP implicitly assumes that packet loss is almost always due to congestion phenomena causing buffer overflows at intermediate routers. Furthermore, it also assumes that nodes are static (i.e., they do not change their position over time). Unfortunately, these assumptions do not hold in MANETs, since in this kind of networks packet losses due to interference and link-layer contentions are largely predominant, and nodes may be mobile. The typical approach to solve these problems is patching TCP to fix its inefficiencies while preserving compatibility with the original protocol. This thesis explores a different approach. Specifically, this thesis presents a new transport protocol (TPA) designed from scratch, and address TCP interoperability at a late design stage. In this way, TPA can include all desired features in a neat and coherent way. This thesis also includes an experimental, as well as, a simulative evaluation of TPA, and a comparison between TCP and TPA performance (in terms of throughput, number of unnecessary transmissions and fairness). The presented analysis considers several of possible configurations of the protocols parameters, different routing protocols, and various networking scenarios. In all the cases taken into consideration TPA significantly outperforms TCP
Distributed Hybrid Simulation of the Internet of Things and Smart Territories
This paper deals with the use of hybrid simulation to build and compose
heterogeneous simulation scenarios that can be proficiently exploited to model
and represent the Internet of Things (IoT). Hybrid simulation is a methodology
that combines multiple modalities of modeling/simulation. Complex scenarios are
decomposed into simpler ones, each one being simulated through a specific
simulation strategy. All these simulation building blocks are then synchronized
and coordinated. This simulation methodology is an ideal one to represent IoT
setups, which are usually very demanding, due to the heterogeneity of possible
scenarios arising from the massive deployment of an enormous amount of sensors
and devices. We present a use case concerned with the distributed simulation of
smart territories, a novel view of decentralized geographical spaces that,
thanks to the use of IoT, builds ICT services to manage resources in a way that
is sustainable and not harmful to the environment. Three different simulation
models are combined together, namely, an adaptive agent-based parallel and
distributed simulator, an OMNeT++ based discrete event simulator and a
script-language simulator based on MATLAB. Results from a performance analysis
confirm the viability of using hybrid simulation to model complex IoT
scenarios.Comment: arXiv admin note: substantial text overlap with arXiv:1605.0487
End-to-End Resilience Mechanisms for Network Transport Protocols
The universal reliance on and hence the need for resilience in network communications has been well established. Current transport protocols are designed to provide fixed mechanisms for error remediation (if any), using techniques such as ARQ, and offer little or no adaptability to underlying network conditions, or to different sets of application requirements. The ubiquitous TCP transport protocol makes too many assumptions about underlying layers to provide resilient end-to-end service in all network scenarios, especially those which include significant heterogeneity. Additionally the properties of reliability, performability, availability, dependability, and survivability are not explicitly addressed in the design, so there is no support for resilience. This dissertation presents considerations which must be taken in designing new resilience mechanisms for future transport protocols to meet service requirements in the face of various attacks and challenges. The primary mechanisms addressed include diverse end-to-end paths, and multi-mode operation for changing network conditions
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
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