7 research outputs found
QoS provisioning in multimedia streaming
Multimedia consists of voice, video, and data. Sample applications include video conferencing, video on demand, distance learning, distributed games, and movies on demand. Providing Quality of Service (QoS) for multimedia streaming has been a difficult and challenging problem. When multimedia traffic is transported over a network, video traffic, though usually compressed/encoded for bandwidth reduction, still consumes most of the bandwidth. In addition, compressed video streams typically exhibit highly variable bit rates as well as long range dependence properties, thus exacerbating the challenge in meeting the stringent QoS requirements of multimedia streaming with high network utilization. Dynamic bandwidth allocation in which video traffic prediction can play an important role is thus needed.
Prediction of the variation of the I frame size using Least Mean Square (LMS) is first proposed. Owing to a smoother sequence, better prediction has been achieved as compared to the composite MPEG video traffic prediction scheme. One problem with this LMS algorithm is its slow convergence. In Variable Bit Rate (VBR) videos characterized by frequent scene changes, the LMS algorithm may result in an extended period of intractability, and thus may experience excessive cell loss during scene changes. A fast convergent non-linear predictor called Variable Step-size Algorithm (VSA) is subsequently proposed to overcome this drawback. The VSA algorithm not only incurs small prediction errors but more importantly achieves fast convergence. It tracks scene changes better than LMS. Bandwidth is then assigned based on the predicted I frame size which is usually the largest in a Group of Picture (GOP). Hence, the Cell Loss Ratio (CLR) can be kept small. By reserving bandwidth at least equal to the predicted one, only prediction errors need to be buffered. Since the prediction error was demonstrated to resemble white noise or exhibits at most short term memory, smaller buffers, less delay, and higher bandwidth utilization can be achieved. In order to further improve network bandwidth utilization, a QoS guaranteed on-line bandwidth allocation is proposed. This method allocates the bandwidth based on the predicted GOP and required QoS. Simulations and analytical results demonstrate that this scheme provides guaranteed delay and achieves higher bandwidth utilization.
Network traffic is generally accepted to be self similar. Aggregating self similar traffic can actually intensify rather than diminish burstiness. Thus, traffic prediction plays an important role in network management. Least Mean Kurtosis (LMK), which uses the negated kurtosis of the error signal as the cost function, is proposed to predict the self similar traffic. Simulation results show that the prediction performance is improved greatly as compared to the LMS algorithm. Thus, it can be used to effectively predict the real time network traffic.
The Differentiated Service (DiffServ) model is a less complex and more scalable solution for providing QoS to IP as compared to the Integrated Service (IntServ) model. We propose to transport MPEG frames through various service classes of DiffServ according to the MPEG video characteristics. Performance analysis and simulation results show that our proposed approach can not only guarantee QoS but can also achieve high bandwidth utilization. As the end video quality is determined not only by the network QoS but also by the encoded video quality, we consider video quality from these two aspects and further propose to transport spatial scalable encoded videos over DiffServ. Performance analysis and simulation results show that this can provision QoS guarantees. The dropping policy we propose at the egress router can reduce the traffic load as well as the risk of congestion in other domains
A Model for Dynamic QoS Negotiation Applied to an MPEG4 Applications
The traffic generated by multimedia applications presents a great amount of burstiness, which can hardly be described by a static set of traffic parameters. The dynamic and efficient usage of the resources is one of the fundamental aspects of multimedia networks: the traffic specification should first reflect the real traffic demand, but optimise, at the same time, the resources requested. This chapter presents: a model for dynamically renegotiating the traffic specification (RVBR), how this can be integrated with the traffic reservation mechanism RSVP, and an example of application able to accommodate its traffic to managing QoS dynamically. The remaining of this chapter is focused on the technique used to implement RVBR) taking into account problems deriving from delay during the renegotiation phase and on the performance of the application with MPEG4 traffic
Congestion control mechanisms within MPLS networks
PhDAbstract not availabl
A quality of service based framework for dynamic, dependable systems
There is currently much UK government and industry interest towards the integration of complex computer-based systems, including those in the military domain. These systems can include both mission critical and safety critical applications, and therefore require the dependable communication of data. Current modular military systems requiring such performance guarantees are mostly based on parameters and system states fixed during design time, thus allowing a predictable estimate of performance. These systems can exhibit a limited degree of reconfiguration, but this is typically within the constraints of a predefined set of configurations. The ability to reconfigure systems more dynamically, could lead to further increased flexibility and adaptability, resulting in the better use of existing assets. Current software architecture models that are capable of providing this flexibility, however, tend to lack support for dependable performance.
This thesis explores the benefits for the dependability of future dynamic systems, built on a publish/subscribe model, from using Quality of Service (QoS) methods to map application level data communication requirements to available network resources. Through this, original contributions to knowledge are created, including; the proposal of a QoS framework that specifies a way of defining flexible levels of QoS characteristics and their use in the negotiation of network resources, a simulation based evaluation of the QoS framework and specifically the choice of negotiation algorithm used, and a test-bed based feasibility study.
Simulation experimentation conducted comparing different methods of QoS negotiation gives a clear indication that the use of the proposed QoS framework and flexible negotiation algorithm can provide a benefit in terms of system utility, resource utilisation, and system stability. The choice of negotiation algorithm has a particularly strong impact on these system properties. The cost of these benefits comes in terms of the processing power and execution time required to reach a decision on the acceptance of a subscriber. It is suggested, given this cost, that when computational resources are limited, a simpler priority based negotiation algorithm should be used. Where system resources are more abundant, however, the flexible negotiation algorithm proposed within the QoS framework can offer further benefits.
Through the implementation of the QoS framework within an existing military avionics software architecture based emulator on a test-bed, both the technical challenges that will need to be overcome and, more importantly, the potential viability for the inclusion of the QoS framework have been demonstrated
CLASS RENEGOTIATING MECHANISM FOR GUARANTEED END-TO-END QOS OVER DIFFSERV NETWORKS
Differentiated-services model has been prevailed as a scalable solution to provide quality of service over the Internet. Many researches have been focused on per hop behavior or a single domain behavior to enhance quality of service. Thus, there are still difficulties in providing the end-to-end guaranteed service when the path between sender and receiver includes multiple domains. Furthermore differentiated-services model mainly considers quality of service for traffic aggregates due to the scalability, and the quality of service state may be time varying according to the network conditions in the case of relative service model, which make the problem more challenging to guarantee the end-to-end quality-of-service. In this paper, we study class renegotiating mechanisms along the path to provide the end-to-end guaranteed quality of service with the minimum networking price over multiple differentiated-service domains. The proposed mechanism includes an effective implementation of relative differentiated-service model, quality of service advertising mechanism and class renegotiating mechanisms. Finally, the experimental results are provided to show the performance of the proposed algorithm.X11sciescopu
Real-time communications over switched Ethernet supporting dynamic QoS management
Doutoramento em Engenharia InformĂĄticaDurante a Ășltima dĂ©cada temos assistido a um crescente aumento na utilização
de sistemas embutidos para suporte ao controlo de processos, de sistemas
robĂłticos, de sistemas de transportes e veĂculos e atĂ© de sistemas domĂłticos
e eletrodomĂ©sticos. Muitas destas aplicaçÔes sĂŁo crĂticas em termos de
segurança de pessoas e bens e requerem um alto nĂvel de determinismo com
respeito aos instantes de execução das respectivas tarefas. Além disso, a implantação
destes sistemas pode estar sujeita a limitaçÔes estruturais, exigindo
ou beneficiando de uma configuração distribuĂda, com vĂĄrios subsistemas
computacionais espacialmente separados. Estes subsistemas, apesar de
espacialmente separados, sĂŁo cooperativos e dependem de uma infraestrutura
de comunicação para atingir os objectivos da aplicação e, por consequĂȘncia,
também as transacçÔes efectuadas nesta infraestrutura estão sujeitas à s
restriçÔes temporais definidas pela aplicação.
As aplicaçÔes que executam nestes sistemas distribuĂdos, chamados
networked embedded systems (NES), podem ser altamente complexas e
heterogéneas, envolvendo diferentes tipos de interacçÔes com diferentes
requisitos e propriedades. Um exemplo desta heterogeneidade Ă© o modelo de
activação da comunicação entre os subsistemas que pode ser desencadeada
periodicamente de acordo com uma base de tempo global (time-triggered),
como sejam os fluxos de sistemas de controlo distribuĂdo, ou ainda ser
desencadeada como consequĂȘncia de eventos assĂncronos da aplicação
(event-triggered). Independentemente das caracterĂsticas do trĂĄfego ou do
seu modelo de activação, é de extrema importùncia que a plataforma de
comunicaçÔes disponibilize as garantias de cumprimento dos requisitos da
aplicação ao mesmo tempo que proporciona uma integração simples dos
vĂĄrios tipos de trĂĄfego.
Uma outra propriedade que estĂĄ a emergir e a ganhar importĂąncia no seio
dos NES é a flexibilidade. Esta propiedade é realçada pela necessidade de
reduzir os custos de instalação, manutenção e operação dos sistemas. Neste
sentido, o sistema Ă© dotado da capacidade para adaptar o serviço fornecido Ă
aplicação aos respectivos requisitos instantùneos, acompanhando a evolução
do sistema e proporcionando uma melhor e mais racional utilização dos
recursos disponĂveis.
No entanto, maior flexibilidade operacional Ă© igualmente sinĂłnimo de
maior complexidade derivada da necessidade de efectuar a alocação dinùmica
dos recursos, acabando também por consumir recursos adicionais no sistema.
A possibilidade de modificar dinĂąmicamente as caracteristicas do sistema
também acarreta uma maior complexidade na fase de desenho e especificação.
O aumento do nĂșmero de graus de liberdade suportados faz aumentar
o espaço de estados do sistema, dificultando a uma pre-anålise. No sentido de
conter o aumento de complexidade sĂŁo necessĂĄrios modelos que representem
a dinĂąmica do sistema e proporcionem uma gestĂŁo optimizada e justa dos
recursos com base em parùmetros de qualidade de serviço (QdS).
Ă nossa tese que as propriedades de flexibilidade, pontualidade e gestĂŁo
dinĂąmica de QdS podem ser integradas numa rede switched Ethernet (SE),
tirando partido do baixo custo, alta largura de banda e fåcil implantação. Nesta
dissertação é proposto um protocolo, Flexible Time-Triggered communication
over Switched Ethernet (FTT-SE), que suporta as propriedades desejadas e
que ultrapassa as limitaçÔes das redes SE para aplicaçÔes de tempo-real tais
como a utilização de filas FIFO, a existĂȘncia de poucos nĂveis de prioridade
e a pouca capacidade de gestĂŁo individualizada dos fluxos. O protocolo
baseia-se no paradigma FTT, que genericamente define a arquitectura de uma
pilha protocolar sobre o acesso ao meio de uma rede partilhada, impondo
desta forma determinismo temporal, juntamente com a capacidade para
reconfiguração e adaptação dinùmica da rede. São ainda apresentados vårios
modelos de distribuição da largura de banda da rede de acordo com o nĂvel de
QdS especificado por cada serviço utilizador da rede.
Esta dissertação expÔe a motivação para a criação do protocolo FTT-SE,
apresenta uma descrição do mesmo, bem como a anålise de algumas das
suas propiedades mais relevantes. SĂŁo ainda apresentados e comparados
modelos de distribuição da QdS. Finalmente, são apresentados dois casos de
aplicaçÔes que sustentam a validade da tese acima mencionada.During the last decade we have witnessed a massive deployment of embedded
systems on a wide applications range, from industrial automation to process
control, avionics, cars or even robotics. Many of these applications have an
inherently high level of criticality, having to perform tasks within tight temporal
constraints. Additionally, the configuration of such systems is often distributed,
with several computing nodes that rely on a communication infrastructure to
cooperate and achieve the application global goals. Therefore, the communications
are also subject to the same temporal constraints set by the application
requirements.
Many applications relying on such networked embedded systems (NES)
are complex and heterogeneous, comprehending different activities with different
requirements and properties. For example, the communication between
subsystems may follow a strict temporal synchronization with respect to a
global time-base (time-triggered), like in a distributed feedback control loop,
or it may be issued asynchronously upon the occurrence of events (eventtriggered).
Regardless of the traffic characteristics and its activation model, it
is of paramount importance having a communication framework that provides
seamless integration of heterogeneous traffic sources while guaranteeing the
application requirements.
Another property that has been emerging as important for NES design and
operation is flexibility. The need to reduce installation and operational costs,
while facilitating maintenance is promoting a more rational use of the available
resources at run-time, exploring the ability to tune service parameters as the
system evolves.
However, such operational flexibility comes with the cost of increasing the
complexity of the system to handle the dynamic resource management, which
on the other hand demands the allocation of additional system resources.
Moreover, the capacity to dynamically modify the system properties also
causes a higher complexity when designing and specifying the system, since
the operational state-space increases with the degrees of flexibility of the
system.
Therefore, in order to bound this complexity appropriate operational models
are needed to handle the system dynamics and carry on an efficient and
fair resource management strategy based on quality of service (QoS) metrics.
This thesis states that the properties of flexibility and timeliness as needed
for dynamic QoS management can be provided to switched Ethernet based
systems. Switched Ethernet, although initially designed for general purpose
Internet access and file transfers, is becoming widely used in NES-based applications.
However, COTS switched Ethernet is insufficient regarding the needs
for real-time predictability and for supporting the aforementioned properties due
the use of FIFO queues too few priority levels and for stream-level management
capabilities. In this dissertation we propose a protocol to overcome those
limitations, namely the Flexible Time-Triggered communication over Switched
Ethernet (FTT-SE). The protocol is based on the FTT paradigm that generically
defines a protocol architecture suitable to enforce real-time determinism on a
communication network supporting the desired flexibility properties.
This dissertation addresses the motivation for FTT-SE, describing the
protocol as well as its schedulability analysis. It additionally covers the resource
distribution topic, where several distribution models are proposed to manage
the resource capacity among the competing services and while considering
the QoS level requirements of each service. A couple of application cases are
shown that support the aforementioned thesis