Many efforts have been carried out to provide transmission reliability in the history of communication systems. As the demand for real-time applications increased, providing a reliable communication in a timely manner for such applications is strongly desired. Considering timing constraints makes the issue of achieving reliability more difficult. This thesis concentrates on providing reliability for real-time communication in embedded networks by achieving a timing analysis and using the ARQ concept. What is carried out in this thesis is providing retransmission in a real-time manner for embedded networks according to application request. The thesis work focuses on one packet retransmission over a point to point link, but the concept is rich and can be extended to cover application request in real-time embedded networks. Two methods have been fulfilled, and a simulation has been done on the timing analysis focusing on the performance in accepting real-time traffic in the form of separate channels for each application request. The protocol combines ARQ and a scheduling algorithm as a base to support retransmission for hard real-time applications in embedded networks.

Applications with timing requirements, such as multimedia and live multi-user interaction, are becoming more prevalent in wide area networks. The desire to provide more predictable performance for such applications in packet switched wide area networks is evident in the channel management provided by Asynchronous Transfer Mode (ATM) networks and in the extensions to the Internet protocols proposed by the Internet Engineering Task Force (IETF) working groups on integrated and differentiated service. The ability to provide guarantees on the performance of traffic flows, such as packet delay and loss characteristics, relies on an accurate model of the traffic arrival and service at each node in the network. This thesis surveys the work in bounding packet delay based on various proposed queuing disciplines and proposes a method for more accurately defining the traffic arrival and worst case backlog experienced by packets. The methods are applied to the first in first out (FIFO) queuing discipline to define equations for determining the worst case backlog and queuing delay in multihop networks. Simulation results show a significant improvement in the accuracy of the delay bounds over existing bounds published in the literature. An improvement of two orders of magnitude can be realised for a ten hop path and the improvement increases exponentially with the length of the path for variable rate network traffic. The equations derived in the thesis also take into consideration the effect of jitter on delay, thereby removing the requirement for rate controllers or traffic shaping within the network. In addition to providing more accurate delay bounds, the problem of providing fault tolerance to channels with guaranteed quality of service (QoS) is also explored. This thesis introduces a method for interleaving resource requirements of backup channels to reduce the overall resource reservations that are required to provide guaranteed fault recovery with the same QoS as the original failed channel. An algorithm for selecting recovery paths that can meet a channel's QoS requirements during recovery is also introduced. / Thesis (Ph.D.)--Computer Science, 2003.

High-performance embedded systems communicating heterogeneous traffic with high bandwidth and strict timing requirements are in need of more efficient communication solutions. This thesis proposes two multi-wavelength passive optical networks able to meet these demands. The networks are based upon a single-hop star topology with an Arrayed Waveguide Grating (AWG) placed in the centre. The intended application areas for the two networks are short range embedded communication systems like System Area Networks (SANs) and router architectures with electronic queuing. The AWG’s attractive property of spatial wavelength reuse, as well as the combination of fixed-tuned and tuneable transceivers in the end nodes, enables simultaneous control and data traffic transmission. This, in turn, makes it possible to support heterogeneous traffic with both hard and soft real-time constraints. Additionally, two Medium Access Control (MAC) protocols, one for each network solution, are developed. Traffic scheduling is centrally controlled by a node, the protocol processor, residing together with the AWG in a hub. All nodes use Earliest Deadline First (EDF) scheduling and communicate with the protocol processor through physical control channels. A case study, including simulations, in the field of Radar Signal Processing (RSP) and simulations using periodic real-time traffic are conducted for the two application areas respectively, showing very good results. Further, a deterministic real-time analysis is conducted to provide throughput and delay guarantees for hard real-time traffic and an increase in guaranteed traffic is achieved through an analysis of existing traffic dependencies in a multichannel network. Simulation results incorporating the traffic dependency analysis indicate a considerable increase in the possible guaranteed throughput of hard real-time traffic.

Future parallel computer systems for embedded real-time applications,where each node in itself can be a parallel computer, are predicted to havevery high bandwidth demands on the interconnection network. Otherimportant properties are time-deterministic latency and guarantees to meetdeadlines. In this thesis, a fiber-optic passive optical star network with amedium access protocol for packet switched communication in distributedreal-time systems is proposed. By using WDM (Wavelength DivisionMultiplexing), multiple channels, each with a capacity of several Gb/s, areobtained. A number of protocols for WDM star networks have recently been proposed.However, the area of real-time protocols for these networks is quiteunexplored. The protocol proposed in this thesis is based on TDMA (TimeDivision Multiple Access) and uses a new distributed slot-allocationalgorithm with real-time properties. Services for both guarantee-seekingmessages and best-effort messages are supported for single destination,multicast, and broadcast transmission. Slot reserving can be used toincrease the time-deterministic bandwidth, while still having an efficientbandwidth utilization due to a simple slot release method. By connecting several clusters of the proposed WDM star network by abackbone star, thus forming a star-of-stars network, we get a modular andscalable high-bandwidth network. The deterministic properties of thenetwork are theoretically analyzed for both intra-cluster and inter-clustercommunication, and computer simulations of intra-cluster communicationare reported. Also, an overview of high-performance fiber-opticcommunication systems is presented.

Video conferencing applications have significantly changed the way in which people communicate over the Internet. Web real-time communication (WebRTC), drafted by the World Wide Web Consortium (W3C) and the Internet Engineering Task Force (IETF), has added new functionality to web browsers, allowing audio/video calls between browsers without the need to install any video telephony applications. The Google Congestion Control (GCC) algorithm has been proposed as WebRTC’s receiver congestion control mechanism, but its performance is limited due to using a fixed incoming rate decrease factor, known as an alpha (α). In this thesis, we have proposed a dynamic alpha model to reduce the receiving bandwidth estimate during overuse, as indicated by the overuse detector. Experiments using our specific testbed show that our proposed model achieves a higher incoming rate and a lower Round-Trip Time while slightly increasing the packet loss rate in some cases compared to fixed alpha model. Our mathematical model proves that it is necessary to use an adaptive alpha α as the receiver side controller. The experimental results show improvement in the term of incoming rate, Round-Trip Time, and packet fraction loss rate in some cases. Our model increases the amount of incoming rate and decreases Round-Trip Time and fraction loss.

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado. / Revisión por pares

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2018-11-13T10:34:43Z No. of bitstreams: 2 Dissertação - Marcelo Barros de Azevedo Vieira - 2018.pdf: 2090852 bytes, checksum: cea29f7c5b0e3e434fef63a6866bc625 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2018-11-13T11:09:32Z (GMT) No. of bitstreams: 2 Dissertação - Marcelo Barros de Azevedo Vieira - 2018.pdf: 2090852 bytes, checksum: cea29f7c5b0e3e434fef63a6866bc625 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2018-11-13T11:09:32Z (GMT). No. of bitstreams: 2 Dissertação - Marcelo Barros de Azevedo Vieira - 2018.pdf: 2090852 bytes, checksum: cea29f7c5b0e3e434fef63a6866bc625 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2018-10-09 / The technological advances in recent years have allowed the development of new applications for communication. These applications allow multiple types of media to be switched between their users, with lower latency providing a better experience for the user. However, the development of applications for communication using general purpose languages has as a focus the development of the application and not the solution of the problems in a domain. In this way, domain-specific modeling languages, originated in Model-Driven Engineering, raise the level of abstraction and reduce the complexity of software development. Specificaly, modeling languages for the real-time communication domain aim to model applications that allow real-time communication among users, not only reducing the development time but also offering users the possibility of creating their own applications. The objective of this work was to propose a new communication modeling language, RBCML, which enables the definition of communication applications based on the roles that users play in a communication session, as well as their requirements in terms of the types of media and data that they can exchange. An implementation of the language was developed on top of the standards-based WebRTC platform in order to carry out evaluation experiments to demonstrate its usability and performance. / Os avanços tecnológicos ocorridos nos últimos anos, permitiram o desenvolvimento de novas aplicações para comunicação. Essas aplicações permitem que diversos tipos de mídia sejam usadas na comunicação entre os usuários, com menor latência e proporcionando uma melhor experiência para o usuário. No entanto, o desenvolvimento de aplicações para comunicação utilizando linguagens de propósito geral tem como característica o foco no desenvolvimento da aplicação e não na resolução de problemas no domínio. Isso motivou o surgimento de linguagens de modelagem específicas de domínio, originadas na Engenharia Dirigida por Modelos, que elevam o nível de abstração e reduzem a complexidade do desenvolvimento de software. Linguagens de modelagem específicas para o domínio de comunicação em tempo real têm como objetivo modelar aplicações que permitam a comunicação em tempo real, reduzindo o esforço no desenvolvimento deste tipo de aplicação e permitindo que os usuários criem suas próprias aplicações. O objetivo deste trabalho foi propor uma nova linguagem de comunicação, RBCML, que permite a definição de aplicações de comunicação com base nos papéis que os usuários desempenham nas sessões de comunicação, bem como em seus requisitos com respeito aos tipos de mídia e dados por meio dos quais a comunicação ocorre. Uma implementação da linguagem foi desenvolvida usando o padrão WebRTC para permitir a realização de experimentos para demonstrar sua usabilidade e desempenho.

Advanced embedded systems can consist of many sensors, actuators and processors that are deployed on one or several boards, while having a demand of interacting with each other and sharing resources. Communication between different components usually has strict timing constraints. There is thus a strong need to provide solutions for time critical communication. This thesis focuses on both the support of real-time services over standard switched Ethernet networks and the improvement of systems' real-time characteristics, such as reducing delay and jitter in processors and on communication links. Switched Ethernet has been chosen in this work because of its major advantages in industry; it supports higher bit-rates than most other current LAN (Local Area Network) technologies, including field buses, still at a low cost. We propose using a star network topology with a single Ethernet switch. Each node is connected to a separate port of the switch via a full-duplex link, thereby eliminating collisions. A solid real-time communication protocol for switched Ethernet networks is proposed in the thesis, including a real-time layer between the Ethernet layer and the TCP/IP suite. The network has the capability of supporting both real-time and non real-time traffic and assuring adaptation to the surrounding protocol standards. Most embedded systems work in a dynamic environment, where the precise behavior of the network traffic can usually not be predicted. To support real-time services, we have chosen the Earliest Deadline scheduling algorithm (EDF) because of its optimality, high efficiency and suitability for being used in adaptive schemes. To be able to increase the amount of guaranteed real-time traffic, the notion of Asymmetric Deadline Partitioning Scheme (ADPS) is introduced. ADPS allows distribution of the end-to-end deadline of a message, sent from any source node in the network to any destination node via the switch, into two sub-deadlines, one for each hop according to the load of the physical link that it must traverse. For the EDF scheduling algorithm, the feasibility test is one of the most important techniques that provides us with information about whether or not the real-time traffic can be guaranteed by the network. With the same computational complexity as the feasibility test, a method has been developed to compute the minimum EDF-feasible deadline for a real-time task. The importance of this method in real-time applications lies in that it can be effectively used to reduce the response times of specific control activities or limit their input-output jitter. To allow more flexibility in the control of delay and jitter in real-time systems, a general approach for reducing task deadlines according to the requirements of individual tasks has been developed. The method allows the user to specify a deadline reduction factor for each task in order to better exploit the available slack according to the tasks' actual requirements. / <p>Ingår även i serien: Technical report. D / Department of Computer Science and Engineering, Chalmers University of Technology, 1653-1787 ; 28</p>

<p>Server-based architectures have recently generated more interests and are currently considered for usage for communication in networks. In parallel, switched Ethernet technology has been widely adopted and used in lots of networked systems. Current requirements of networks for supporting real-time guarantees while being flexible at the same time have made the network designers to consider addition of some features to common switches. The FTT-Enabled Ethernet switch is a switch that has been developed to support the FTT (Flexible Time Triggered) paradigm. Recently, servers have been added in these types of switches in order to efficiently manage their allocated bandwidth to different types of messages.</p><p>A hierarchical network of Ethernet switches might be designed in different ways according to the overall goals and properties of the network. In this thesis, after a study on different design solutions, an architecture has been proposed based on FTT-enabled switches, motivated by their support of real-time constraints and server-based communication features. After having created the architecture, a protocol for bandwidth reservation for this hierarchically composed Ethernet switch architecture is developed. Behavior of the designed protocol is described in detail and it has been modeled using Uppaal. Moreover, the temporal behavior (timing) of the network is presented.</p>

<p>Switched Ethernet is an Ethernet LAN that uses switches to connect individual nodes. </p><p>This is popular because of its effective and convenient way of extending the bandwidth of </p><p>existing Ethernets. Switched Ethernet is being considered by the industry community because </p><p>of its open standardization, cost effectiveness, and the support for higher data rates up to </p><p>10Gbps. Even though many special-purposed solutions were proposed to support time </p><p>constrained communication over Switched Ethernet, still there were some doubts about the </p><p>real time handling capability of Switched Ethernet. To achieve reliable transmission </p><p>guarantees for real time traffic over Switched Ethernet, it is important to measure the </p><p>performance of Switched Ethernet networks for real time communication. In this thesis work </p><p>we have observed the average end-to-end packet delay for real time traffic over a Switched </p><p>Ethernet by simulation, which is very much essential for real time communication in </p><p>industrial applications, where the communication is time-deterministic. In our thesis we used </p><p>FCFS priority queuing in both the source nodes and switch. In this thesis we also discussed </p><p>about the feasibility analysis for fixed sized frames and some traffic handling methods. We </p><p>used 100mbp/s single full duplex Ethernet switch for our simulation. Finally simulation </p><p>analysis and simulation results are discussed. Our purpose of simulation of Switched Ethernet </p><p>networks is of good importance for the real time industrial applications.</p>