51 research outputs found
Real-time communications over switched Ethernet supporting dynamic QoS management
Doutoramento em Engenharia InformáticaDurante a última década temos assistido a um crescente aumento na utilização
de sistemas embutidos para suporte ao controlo de processos, de sistemas
robóticos, de sistemas de transportes e veículos e até de sistemas domóticos
e eletrodomésticos. Muitas destas aplicações são críticas em termos de
segurança de pessoas e bens e requerem um alto nível de determinismo com
respeito aos instantes de execução das respectivas tarefas. Além disso, a implantação
destes sistemas pode estar sujeita a limitações estruturais, exigindo
ou beneficiando de uma configuração distribuída, com vários subsistemas
computacionais espacialmente separados. Estes subsistemas, apesar de
espacialmente separados, são cooperativos e dependem de uma infraestrutura
de comunicação para atingir os objectivos da aplicação e, por consequência,
também as transacções efectuadas nesta infraestrutura estão sujeitas às
restrições temporais definidas pela aplicação.
As aplicações que executam nestes sistemas distribuídos, chamados
networked embedded systems (NES), podem ser altamente complexas e
heterogéneas, envolvendo diferentes tipos de interacções com diferentes
requisitos e propriedades. Um exemplo desta heterogeneidade é 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 distribuído, ou ainda ser
desencadeada como consequência de eventos assíncronos da aplicação
(event-triggered). Independentemente das características do tráfego ou do
seu modelo de activação, é de extrema importância que a plataforma de
comunicações disponibilize as garantias de cumprimento dos requisitos da
aplicação ao mesmo tempo que proporciona uma integração simples dos
vários tipos de tráfego.
Uma outra propriedade que está a emergir e a ganhar importância 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 é dotado da capacidade para adaptar o serviço fornecido à
aplicação aos respectivos requisitos instantâneos, acompanhando a evolução
do sistema e proporcionando uma melhor e mais racional utilização dos
recursos disponíveis.
No entanto, maior flexibilidade operacional é igualmente sinónimo de
maior complexidade derivada da necessidade de efectuar a alocação dinâmica
dos recursos, acabando também por consumir recursos adicionais no sistema.
A possibilidade de modificar dinâmicamente as caracteristicas do sistema
também acarreta uma maior complexidade na fase de desenho e especificação.
O aumento do número de graus de liberdade suportados faz aumentar
o espaço de estados do sistema, dificultando a uma pre-análise. No sentido de
conter o aumento de complexidade são necessários modelos que representem
a dinâmica do sistema e proporcionem uma gestão optimizada e justa dos
recursos com base em parâmetros de qualidade de serviço (QdS).
É nossa tese que as propriedades de flexibilidade, pontualidade e gestão
dinâmica de QdS podem ser integradas numa rede switched Ethernet (SE),
tirando partido do baixo custo, alta largura de banda e fácil 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 limitações das redes SE para aplicações de tempo-real tais
como a utilização de filas FIFO, a existência de poucos níveis de prioridade
e a pouca capacidade de gestão 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 dinâmica da rede. São ainda apresentados vários
modelos de distribuição da largura de banda da rede de acordo com o nível de
QdS especificado por cada serviço utilizador da rede.
Esta dissertação expõe a motivação para a criação do protocolo FTT-SE,
apresenta uma descrição do mesmo, bem como a análise de algumas das
suas propiedades mais relevantes. São ainda apresentados e comparados
modelos de distribuição da QdS. Finalmente, são apresentados dois casos de
aplicações 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
FTT-Ethernet: A Flexible Real-Time Communication Protocol that Supports Dynamic QoS Management on Ethernet-based Systems
Ethernet was not originally developed to meet the
requirements of real-time industrial automation systems and
it was commonly considered unsuited for applications at the
field level. Hence, several techniques were developed to make
this protocol exhibit real-time behavior, some of them requiring
specialized hardware, others providing soft-real-time guarantees
only, or others achieving hard real-time guarantees with
different levels of bandwidth efficiency. More recently, there has
been an effort to support quality-of-service (QoS) negotiation
and enforcement but there is not yet an Ethernet-based data
link protocol capable of providing dynamic QoS management
to further exploit the variable requirements of dynamic applications.
This paper presents the FTT-Ethernet protocol, which
efficiently supports hard-real-time operation in a flexible way,
seamlessly over shared or switched Ethernet. The FTT-Ethernet
protocol employs an efficient master/multislave transmission
control technique and combines online scheduling with online
admission control, to guarantee continued real-time operation
under dynamic communication requirements, together with data
structures and mechanisms that are tailored to support dynamic
QoS management. The paper includes a sample application,
aiming at the management of video streams, which highlights
the protocol’s ability to support dynamic QoS management with
real-time guarantees
Comparing Admission Control Architectures for Real-Time Ethernet
Industry 4.0 and Autonomous Driving are emerging resource-intensive distributed application domains that deal with open and evolving environments. These systems are subject to stringent resource, timing, and other non-functional constraints, as well as frequent reconfiguration. Thus, real-time behavior must not preclude operational flexibility. This combination is motivating ongoing efforts within the Time Sensitive Networking (TSN) standardization committee to define admission control mechanisms for Ethernet. Existing mechanisms in TSN, like those of AVB, its predecessor, follow a distributed architecture that favors scalability. Conversely, the new mechanisms envisaged for TSN (IEEE 802.1Qcc) follow a (partially) centralized architecture, favoring short reconfiguration latency. This paper shows the first quantitative comparison between distributed and centralized admission control architectures concerning reconfiguration latency. Here, we compare AVB against a dynamic real-time reconfigurable Ethernet technology with centralized management, namely HaRTES. Our experiments show a significantly lower latency using the centralized architecture. We also observe the dependence of the distributed architecture in the end nodes' performance and the benefit of having a protected channel for the admission control transactions.This work was supported in part by the Spanish Agencia Estatal de Investigación (AEI), in part by the Fondo Europeo de Desarrollo
Regional (FEDER) [AEI/FEDER, Unión Europea (UE)] under Grant TEC2015-70313-R, in part by the European Regional Development
Fund (FEDER) through the Operational Programme for Competitivity and the Internationalization of Portugal 2020 Partnership Agreement
(PRODUTECH-SIF) under Grant POCI-01-0247-FEDER-024541, and in part by the Research Centre Instituto de Telecomunicações under
Grant UID/EEA/50008/2013.info:eu-repo/semantics/publishedVersio
Proceedings Work-In-Progress Session of the 13th Real-Time and Embedded Technology and Applications Symposium
The Work-In-Progress session of the 13th IEEE Real-Time and Embedded Technology and Applications Symposium (RTAS\u2707) presents papers describing contributions both to state of the art and state of the practice in the broad field of real-time and embedded systems. The 17 accepted papers were selected from 19 submissions. This proceedings is also available as Washington University in St. Louis Technical Report WUCSE-2007-17, at http://www.cse.seas.wustl.edu/Research/FileDownload.asp?733. Special thanks go to the General Chairs – Steve Goddard and Steve Liu and Program Chairs - Scott Brandt and Frank Mueller for their support and guidance
Just a Second -- Scheduling Thousands of Time-Triggered Streams in Large-Scale Networks
Deterministic real-time communication with bounded delay is an essential
requirement for many safety-critical cyber-physical systems, and has received
much attention from major standardization bodies such as IEEE and IETF. In
particular, Ethernet technology has been extended by time-triggered scheduling
mechanisms in standards like TTEthernet and Time-Sensitive Networking. Although
the scheduling mechanisms have become part of standards, the traffic planning
algorithms to create time-triggered schedules are still an open and challenging
research question due to the problem's high complexity. In particular,
so-called plug-and-produce scenarios require the ability to extend schedules on
the fly within seconds. The need for scalable scheduling and routing algorithms
is further supported by large-scale distributed real-time systems like smart
energy grids with tight communication requirements. In this paper, we tackle
this challenge by proposing two novel algorithms called Hierarchical Heuristic
Scheduling (H2S) and Cost-Efficient Lazy Forwarding Scheduling (CELF) to
calculate time-triggered schedules for TTEthernet. H2S and CELF are highly
efficient and scalable, calculating schedules for more than 45,000 streams on
random networks with 1,000 bridges as well as a realistic energy grid network
within sub-seconds to seconds
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