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Computing infrastructure issues in distributed communications systems : a survey of operating system transport system architectures
The performance of distributed applications (such as file transfer, remote login, tele-conferencing, full-motion video, and scientific visualization) is influenced by several factors that interact in complex ways. In particular, application performance is significantly affected both by communication infrastructure factors and computing infrastructure factors. Several communication infrastructure factors include channel speed, bit-error rate, and congestion at intermediate switching nodes. Computing infrastructure factors include (among other things) both protocol processing activities (such as connection management, flow control, error detection, and retransmission) and general operating system factors (such as memory latency, CPU speed, interrupt and context switching overhead, process architecture, and message buffering). Due to a several orders of magnitude increase in network channel speed and an increase in application diversity, performance bottlenecks are shifting from the network factors to the transport system factors.This paper defines an abstraction called an "Operating System Transport System Architecture" (OSTSA) that is used to classify the major components and services in the computing infrastructure. End-to-end network protocols such as TCP, TP4, VMTP, XTP, and Delta-t typically run on general-purpose computers, where they utilize various operating system resources such as processors, virtual memory, and network controllers. The OSTSA provides services that integrate these resources to support distributed applications running on local and wide area networks.A taxonomy is presented to evaluate OSTSAs in terms of their support for protocol processing activities. We use this taxonomy to compare and contrast five general-purpose commercial and experimental operating systems including System V UNIX, BSD UNIX, the x-kernel, Choices, and Xinu
Topology design and performance analysis of an integrated communication network
A research study on the topology design and performance analysis for the Space Station Information System (SSIS) network is conducted. It is begun with a survey of existing research efforts in network topology design. Then a new approach for topology design is presented. It uses an efficient algorithm to generate candidate network designs (consisting of subsets of the set of all network components) in increasing order of their total costs, and checks each design to see if it forms an acceptable network. This technique gives the true cost-optimal network, and is particularly useful when the network has many constraints and not too many components. The algorithm for generating subsets is described in detail, and various aspects of the overall design procedure are discussed. Two more efficient versions of this algorithm (applicable in specific situations) are also given. Next, two important aspects of network performance analysis: network reliability and message delays are discussed. A new model is introduced to study the reliability of a network with dependent failures. For message delays, a collection of formulas from existing research results is given to compute or estimate the delays of messages in a communication network without making the independence assumption. The design algorithm coded in PASCAL is included as an appendix
Modelação e simulação de equipamentos de rede para Indústria 4.0
Currently, the industrial sector has increasingly opted for digital technologies
in order to automate all its processes. This development comes from
notions like Industry 4.0 that redefines the way these systems are designed.
Structurally, all the components of these systems are connected in a complex
network known as the Industrial Internet of Things. Certain requirements
arise from this concept regarding industrial communication networks. Among
them, the need to ensure real-time communications, as well as support for
dynamic resource management, are extremely relevant. Several research
lines pursued to develop network technologies capable of meeting such
requirements. One of these protocols is the Hard Real-Time Ethernet Switch
(HaRTES), an Ethernet switch with support for real-time communications and
dynamic resource management, requirements imposed by Industry 4.0.
The process of designing and implementing industrial networks can,
however, be quite time consuming and costly. These aspects impose
limitations on testing large networks, whose level of complexity is higher and
requires the usage of more hardware. The utilization of network simulators
stems from the necessity to overcome such restrictions and provide tools to
facilitate the development of new protocols and evaluation of communications
networks.
In the scope of this dissertation a HaRTES switch model was developed
in the OMNeT++ simulation environment. In order to demonstrate a
solution that can be employed in industrial real-time networks, this dissertation
presents the fundamental aspects of the implemented model as well as a set
of experiments that compare it with an existing laboratory prototype, with the
objective of validating its implementation.Atualmente o setor industrial tem vindo cada vez mais a optar por tecnologias
digitais de forma a automatizar todos os seus processos. Este desenvolvimento
surge de noções como Indústria 4.0, que redefine o modo de como
estes sistemas são projetados. Estruturalmente, todos os componentes
destes sistemas encontram-se conectados numa rede complexa conhecida
como Internet Industrial das Coisas. Certos requisitos advêm deste conceito,
no que toca às redes de comunicação industriais, entre os quais se destacam
a necessidade de garantir comunicações tempo-real bem como suporte a
uma gestão dinâmica dos recursos, os quais são de extrema importância.
Várias linhas de investigação procuraram desenvolver tecnologias de rede
capazes de satisfazer tais exigências. Uma destas soluções é o "Hard
Real-Time Ethernet Switch" (HaRTES), um switch Ethernet com suporte a
comunicações de tempo-real e gestão dinâmica de Qualidade-de-Serviço
(QoS), requisitos impostos pela Indústria 4.0.
O processo de projeto e implementação de redes industriais pode, no
entanto, ser bastante moroso e dispendioso. Tais aspetos impõem limitações
no teste de redes de largas dimensões, cujo nível de complexidade é
mais elevado e requer o uso de mais hardware. Os simuladores de redes
permitem atenuar o impacto de tais limitações, disponibilizando ferramentas
que facilitam o desenvolvimento de novos protocolos e a avaliação de redes
de comunicações.
No âmbito desta dissertação desenvolveu-se um modelo do switch HaRTES
no ambiente de simulação OMNeT++. Com um objetivo de demonstrar uma
solução que possa ser utilizada em redes de tempo-real industriais, esta
dissertação apresenta os aspetos fundamentais do modelo implementado
bem como um conjunto de experiências que o comparam com um protótipo
laboratorial já existente, no âmbito da sua validação.Mestrado em Engenharia Eletrónica e Telecomunicaçõe
Is the Web ready for HTTP/2 Server Push?
HTTP/2 supersedes HTTP/1.1 to tackle the performance challenges of the modern
Web. A highly anticipated feature is Server Push, enabling servers to send data
without explicit client requests, thus potentially saving time. Although
guidelines on how to use Server Push emerged, measurements have shown that it
can easily be used in a suboptimal way and hurt instead of improving
performance. We thus tackle the question if the current Web can make better use
of Server Push. First, we enable real-world websites to be replayed in a
testbed to study the effects of different Server Push strategies. Using this,
we next revisit proposed guidelines to grasp their performance impact. Finally,
based on our results, we propose a novel strategy using an alternative server
scheduler that enables to interleave resources. This improves the visual
progress for some websites, with minor modifications to the deployment. Still,
our results highlight the limits of Server Push: a deep understanding of web
engineering is required to make optimal use of it, and not every site will
benefit.Comment: More information available at https://push.netray.i
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
Ada (trademark) projects at NASA. Runtime environment issues and recommendations
Ada practitioners should use this document to discuss and establish common short term requirements for Ada runtime environments. The major current Ada runtime environment issues are identified through the analysis of some of the Ada efforts at NASA and other research centers. The runtime environment characteristics of major compilers are compared while alternate runtime implementations are reviewed. Modifications and extensions to the Ada Language Reference Manual to address some of these runtime issues are proposed. Three classes of projects focusing on the most critical runtime features of Ada are recommended, including a range of immediately feasible full scale Ada development projects. Also, a list of runtime features and procurement issues is proposed for consideration by the vendors, contractors and the government
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