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Real time communications over 802.11: Rt-wmp
- in Proc. IEEE Internatonal Conference on Mobile Adhoc and Sensor Systems MASS 2007, 2007
"... Ad-hoc networks usually support best-effort traffic and occasionally some kind of Quality of Service (QoS). How-ever, there are some applications, which generally involve cooperative control, with hard real-time traffic require-ments where strict deadlines must be met. To meet dead-lines, the commun ..."
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Ad-hoc networks usually support best-effort traffic and occasionally some kind of Quality of Service (QoS). How-ever, there are some applications, which generally involve cooperative control, with hard real-time traffic require-ments where strict deadlines must be met. To meet dead-lines, the communication network has to support the timely delivery of inter-task messages. This is the case, for exam-ple, of applications involving cooperative robot teams, such as those used for rescue tasks in hostile environments, emer-gencies or disaster recovery, where a wired backbone is in-feasible or economically unviable. In this paper, we present RT-WMP, a novel protocol that allows wireless real-time traffic in relatively small mobile ad-hoc networks using the low-cost commercial 802.11 technology. The protocol is based on a token-passing approach and message exchange is priority based. Moreover, support for frequent topology changes is provided through the sharing of a matrix that describes link quality amongst the members of the network. 1.
Interchangeable Scheduling Policies in Real-Time Middleware for Distribution
"... Abstract. When a middleware layer is designed for providing semi-transparent distribution facilities to real-time applications, a trade-off must be made between the expressiveness and control capabilities of the real-time parameters used, and the simplicity of usage. Middleware specifications such a ..."
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Abstract. When a middleware layer is designed for providing semi-transparent distribution facilities to real-time applications, a trade-off must be made between the expressiveness and control capabilities of the real-time parameters used, and the simplicity of usage. Middleware specifications such as RT-CORBA or Ada’s Distributed Systems Annex (DSA) rely on the use of priorities to map the timing requirements of the application, thus restricting the possible scheduling policies. This paper presents a generic technique to express complex scheduling and timing parameters of distributed transactions, allowing real-time middleware implementations to change their scheduling policies for both the processing nodes and the networks. The technique has been tested in an implementation of Ada’s DSA, providing two interchangeable policies: a fixed-priority scheduler, and a complex contract-based flexible scheduler. 1
Integration of a flexible time triggered network in the FRESCOR resource contracting
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Survey of Real-Time Communication in CSMA-Based Networks
- Network Protocols and Algorithms
, 2010
"... The purpose of this paper is to survey the state-of-the-art on real-time (RT) communication in CSMA-based networks and to identify the most suitable approaches to deal with the requirements imposed by next generation communication environments. The paper focuses in the two of the most relevant solut ..."
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The purpose of this paper is to survey the state-of-the-art on real-time (RT) communication in CSMA-based networks and to identify the most suitable approaches to deal with the requirements imposed by next generation communication environments. The paper focuses in the two of the most relevant solutions that operate in shared broadcast environments, according to the CSMA medium access protocol (IEEE 802.3/802.11). RT communication solutions are classified according to two classification axes. The first axis is related to how collisions are dealt with. A second classification axis is related to the compatibility degree achieved by each of the proposed approaches. Finally, a RT communication framework that is adequate to support RT communication in shared environments is briefly discussed.
Adding Contract-Based Reservation Services to a Hard Real-Time Ethernet Protocol
"... This paper presents the implementation of DFSF, a contract-based framework for flexible scheduling in real-time networks. The initial implementation of DFSF provides the ability to make dynamic bandwidth reservations using a distributed acceptance test that ensures the overall network schedulability ..."
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This paper presents the implementation of DFSF, a contract-based framework for flexible scheduling in real-time networks. The initial implementation of DFSF provides the ability to make dynamic bandwidth reservations using a distributed acceptance test that ensures the overall network schedulability. It has been implemented using the Real-Time Ethernet Protocol (RT-EP), which is a software-based token-passing Ethernet protocol for real-time applications, that does not require any modification to existing Ethernet
Ada-CCM: Component-based Technology for Distributed Real-Time Systems
"... Abstract: This paper proposes a technology for the development of distributed real-time component-based applications, which takes advantage of the features that Ada offers for the development of applications with predictable temporal behaviour, and which can be executed in embedded platforms with li ..."
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Abstract: This paper proposes a technology for the development of distributed real-time component-based applications, which takes advantage of the features that Ada offers for the development of applications with predictable temporal behaviour, and which can be executed in embedded platforms with limited resources. The technology uses the Deployment and Configuration of Component-based Distributed Applications Specification of the OMG for describing the components, the execution platforms and the applications. The framework defined in the Lightweight CCM standard of the OMG is taken as the basis of the internal architecture of the components and the applications. It has been extended with a number of features to make the temporal behaviour of the applications predictable. Among these extensions, the usage of CORBA has been replaced by special distributed components, called connectors, which implement the interaction between components by means of predictable and customizable communication services. Besides, special mechanisms have been introduced in the environment to make the threading characteristics of the components configurable. The technology fixes the responsibilities and the knowledge required by each actor involved in the component-based development process, and for each of them it defines the input and output artifacts that they have to manage. Keywords: Ada 2005, Component-based, embedded systems, real-time, OMG 1
Bandwidth Isolation for Composability in Fixed Priority Real-Time Networks
"... The increasing complexity of real-time systems has motivated the application of component-based software engineering principles during the last few years. Temporal encapsulation is key to smoothing the integration stage of software components in complex distributed hard real-time systems. This paper ..."
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The increasing complexity of real-time systems has motivated the application of component-based software engineering principles during the last few years. Temporal encapsulation is key to smoothing the integration stage of software components in complex distributed hard real-time systems. This paper presents a network scheduling server algorithm to guarantee and at the same time limit the network bandwidth assigned to streams of messages with different real-time requirements in a fixed priority network. The algorithm is based on a recently corrected version of the POSIX sporadic server whose rules, originally intended for scheduling tasks, have been adapted and optimized for the special case of fixed-priority networks. The algorithm is able to provide bounded response times that can be analyzed with off-the-shelf real-time analysis tools and can be used for both synchronous and asynchronous messages. The proposed approach has been implemented and evaluated on real hardware, using the CAN bus. The performance evaluation results show that bandwidth isolation can be achieved with rather low overhead both on the processor and the network resources. 1.
WATERS 2011 51 Modeling Real-Time Networks with MAST2
"... Abstract 1 Switched networks have an increasingly important role in real-time communications. The IEEE ethernet standards have defined prioritized traffic (802.1p) and other QoS mechanisms (802.1q). The Avionics Full-Duplex Switched Ethernet (AFDX) standard defines a hard real-time network based on ..."
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Abstract 1 Switched networks have an increasingly important role in real-time communications. The IEEE ethernet standards have defined prioritized traffic (802.1p) and other QoS mechanisms (802.1q). The Avionics Full-Duplex Switched Ethernet (AFDX) standard defines a hard real-time network based on switched ethernet. In the process of defining the new MAST2 model, the network elements have been enhanced to include switches and routers. This paper introduces the schedulability model that will enable an automatic schedulability analysis of an application using switched networks.
ISBN: 978-84-691-2813-8
"... Resumen. Se describe una tecnología para el desarrollo de aplicaciones distribuidas y de tiempo real basadas en componentes, que pueden ser ejecutadas en plataformas con diferentes soportes de comunicación. Hace uso de la especificación D&C de OMG para describir los componentes, las aplicaciones ..."
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Resumen. Se describe una tecnología para el desarrollo de aplicaciones distribuidas y de tiempo real basadas en componentes, que pueden ser ejecutadas en plataformas con diferentes soportes de comunicación. Hace uso de la especificación D&C de OMG para describir los componentes, las aplicaciones y las plataformas de ejecución. Utiliza el modelo de referencia ligero de CCM de OMG (LwCCM framework) como base de la arquitectura interna de los componentes y de las aplicaciones, pero elimina la dependencia del middleware CORBA sustituyéndolo por componentes distribuidos que se denominan conectores, cuyo código se genera de forma automática a partir de la especificación de los componentes y que encapsulan el mecanismo de comunicación que realiza la invocación remota entre componentes. La tecnología ha sido diseñada para garantizar requisitos de tiempo real en su especificación. La tecnología remarca e independiza las responsabilidades y el conocimiento que se requiere de los actores involucrados en el desarrollo de una aplicación basada en componentes. Para cada uno de ellos, define los productos de entrada y de salida sobre los que
