782 research outputs found
Best effort measurement based congestion control
Abstract available: p.
Voice technology and BBN
The following research was discussed: (1) speech signal processing; (2) automatic speech recognition; (3) continuous speech understanding; (4) speaker recognition; (5) speech compression; (6) subjective and objective evaluation of speech communication system; (7) measurement of the intelligibility and quality of speech when degraded by noise or other masking stimuli; (8) speech synthesis; (9) instructional aids for second-language learning and for training of the deaf; and (10) investigation of speech correlates of psychological stress. Experimental psychology, control systems, and human factors engineering, which are often relevant to the proper design and operation of speech systems are described
Intelligent Routing for Software-Defined Media Networks
The multimedia market is an industry with an ever-growing demand coupled with strict requirements. Be it in live streaming services or file content broadcast, multimedia providers need to deliver the best possible quality in order to meet their costumer’s requirements and gain or keep their trust. Multimedia traffic has a high impact on networks and, due to its nature, is sensitive to congestion or hardware failure. Thus, it is frequently that multimedia providers resort to third-party software to monitor quality parameters.
Skyline Communications’ DataMiner® offers network monitoring, orchestrating and automation capabilities across a broad range of applications and environments. These features are enabled by the emergence of Software-Defined Networking (SDN) which provides a global view of networks and the ability to change network properties through software applications. This contrasts with traditional networks which are rigid, static and difficult to scale-up.
An application that greatly benefits from the global network view of SDN is routing optimization. Through routing optimization, a network can effectively deliver more traffic by efficiently balancing load across the different links and paths between end points of a service, reaching an increased performance in data transport.
This dissertation comes to light with the goal of optimizing DataMiner’s routing mechanism by exploring the routing optimization possibilities enabled by its SDN-like architecture. Both link cost optimization-based and Machine Learning (ML) approaches are evaluated as possible solutions to Skyline’s problem and several experiments were conducted to compare them and understand their impact on network performance while
transporting multimedia streams.O mercado audiovisual Ă© uma indĂşstria onde a procura está em constante crescimento, bem como a exigĂŞncia. Tanto durante transmissões ao vivo como de conteĂşdo multimĂ©dia prĂ©-gravado, os provedores de multimĂ©dia necessitam de garantir a melhor qualidade possĂvel para corresponderem aos requisitos dos seus clientes e conquistarem ou manterem a sua confiança nos seus serviços. O tráfego multimĂ©dia tem um forte impacto nas redes que o transportam e, graças Ă sua natureza, Ă© bastante sensĂvel a congestĂŁo ou a falhas de equipamento. Por este motivo, Ă© frequente os provedores de multimĂ©dia recorrerem a
aplicações externas para monitorização de parâmetros de qualidade.
O DataMiner®, desenvolvido pela Skyline Communications, oferece a capacidade de monitorizar e orquestrar redes de transporte de multimĂ©dia bem como de automatizar as suas funcionalidades num vasto conjunto de enquadramentos e ambientes. Tais funcionalidades sĂŁo oferecidas pelo aparecimento de SDN que permite que se tenha uma visĂŁo global de uma rede e que se altere de forma flexĂvel as suas definições atravĂ©s de
aplicações. As caracterĂsticas de redes deste tipo contrastam fortemente com as redes tradicionais marcadas pela sua rigidez, estaticidade e dificuldade de expansĂŁo.
Uma área que beneficia bastante com a visĂŁo global de redes oferecida pela tecnologia de SDN Ă© a otimização do transporte de dados. Desta forma, uma rede consegue transportar mais dados de forma eficiente atravĂ©s do balanceamento da carga a que Ă© submetida pelas diferentes ligações entre elementos e caminhos que conectam pontos de entrada e saĂda da mesma, atingindo altos nĂveis de desempenho.
A presente dissertação surge da intenção da Skyline de otimizar o seu algoritmo de encaminhamento atravĂ©s da exploração de mĂ©todos alternativos introduzidos pela tecnologia de SDN. Tanto mĂ©todos baseados em otimização do custo de ligações da rede como em aprendizagem automática sĂŁo avaliados como possĂveis soluções para o problema proposto e diversas simulações sĂŁo conduzidas para as comparar e averiguar o seu impacto no desempenho de redes de transporte de dados multimĂ©dia
Performance measurement methodology for integrated services networks
With the emergence of advanced integrated services networks, the need for effective
performance analysis techniques has become extremely important. Further
advancements in these networks can only be possible if the practical performance
issues of the existing networks are clearly understood. This thesis is concerned with
the design and development of a measurement system which has been implemented on
a large experimental network.
The measurement system is based on dedicated traffic generators which have been
designed and implemented on the Project Unison network. The Unison project is a
multisite networking experiment for conducting research into the interconnection and
interworking of local area network based multi-media application systems. The traffic
generators were first developed for the Cambridge Ring based Unison network. Once
their usefulness and effectiveness was proven, high performance traffic generators
using transputer technology were built for the Cambridge Fast Ring based Unison
network. The measurement system is capable of measuring the conventional
performance parameters such as throughput and packet delay, and is able to
characterise the operational performance of network bridging components under
various loading conditions. In particular, the measurement system has been used in a
'measure and tune' fashion in order to improve the performance of a complex bridging
device.
Accurate measurement of packet delay in wide area networks is a recognised problem.
The problem is associated with the synchronisation of the clocks between the distant
machines. A chronological timestamping technique has been introduced in which the
clocks are synchronised using a broadcast synchronisation technique. Rugby time
clock receivers have been interfaced to each generator for the purpose of
synchronisation.
In order to design network applications, an accurate knowledge of the expected
network performance under different loading conditions is essential. Using the
measurement system, this has been achieved by examining the network characteristics
at the network/user interface. Also, the generators are capable of emulating a variety
of application traffic which can be injected into the network along with the traffic
from real applications, thus enabling user oriented performance parameters to be
evaluated in a mixed traffic environment.
A number of performance measurement experiments have been conducted using the
measurement system. Experimental results obtained from the Unison network serve to
emphasise the power and effectiveness of the measurement methodology
Resource allocation and scalability in dynamic wavelength-routed optical networks.
This thesis investigates the potential benefits of dynamic operation of wavelength-routed optical networks (WRONs) compared to the static approach. It is widely believed that dynamic operation of WRONs would overcome the inefficiencies of the static allocation in improving resource use. By rapidly allocating resources only when and where required, dynamic networks could potentially provide the same service that static networks but at decreased cost, very attractive to network operators. This hypothesis, however, has not been verified. It is therefore the focus of this thesis to investigate whether dynamic operation of WRONs can save significant number of wavelengths compared to the static approach whilst maintaining acceptable levels of delay and scalability. Firstly, the wavelength-routed optical-burst-switching (WR-OBS) network architecture is selected as the dynamic architecture to be studied, due to its feasibility of implementation and its improved network performance. Then, the wavelength requirements of dynamic WR-OBS are evaluated by means of novel analysis and simulation and compared to that of static networks for uniform and non-uniform traffic demand. It is shown that dynamic WR-OBS saves wavelengths with respect to the static approach only at low loads and especially for sparsely connected networks and that wavelength conversion is a key capability to significantly increase the benefits of dynamic operation. The mean delay introduced by dynamic operation of WR-OBS is then assessed. The results show that the extra delay is not significant as to violate end-to-end limits of time-sensitive applications. Finally, the limiting scalability of WR-OBS as a function of the lightpath allocation algorithm computational complexity is studied. The trade-off between the request processing time and blocking probability is investigated and a new low-blocking and scalable lightpath allocation algorithm which improves the mentioned trade-off is proposed. The presented algorithms and results can be used in the analysis and design of dynamic WRONs
Improved algorithms for TCP congestion control
Reliable and efficient data transfer on the Internet is an important issue. Since late
70’s the protocol responsible for that has been the de facto standard TCP, which
has proven to be successful through out the years, its self-managed congestion
control algorithms have retained the stability of the Internet for decades. However,
the variety of existing new technologies such as high-speed networks (e.g. fibre
optics) with high-speed long-delay set-up (e.g. cross-Atlantic links) and wireless
technologies have posed lots of challenges to TCP congestion control algorithms.
The congestion control research community proposed solutions to most of these
challenges. This dissertation adds to the existing work by: firstly tackling the highspeed
long-delay problem of TCP, we propose enhancements to one of the existing
TCP variants (part of Linux kernel stack). We then propose our own variant:
TCP-Gentle. Secondly, tackling the challenge of differentiating the wireless loss
from congestive loss in a passive way and we propose a novel loss differentiation
algorithm which quantifies the noise in packet inter arrival times and use this
information together with the span (ratio of maximum to minimum packet inter
arrival times) to adapt the multiplicative decrease factor according to a predefined
logical formula. Finally, extending the well-known drift model of TCP to account
for wireless loss and some hypothetical cases (e.g. variable multiplicative decrease),
we have undertaken stability analysis for the new version of the model
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Modeling and simulation of data communication networks using SARA
The selection of an appropriate simulation language can have a profound impact on the success of a simulation study. The available options range from domain-specific simulation languages to general-purpose programming languages. These languages are often supported by a collection of tools which form a simulation system. This paper examines UCLA's SARA (Systems ARchitects' Apprentice) system and explores its' usefulness in modeling and simulating a data communications network. Based on experimental use of SARA's tools, the system is evaluated with respect to required expertise, modeling power, as well as measurement and reporting capability
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