Substation Automation Systems (SAS) integrate technologies, protocols, and processes to monitor, control, and protect electrical equipment in power substations. These systems rely on Intelligent Electronic Devices (IEDs) and centralized interfaces to enhance efficiency, reliability, and response times. While standards like IEC 61850 and ISO/IEC 9506 define communication protocols, gaps remain, particularly regarding wireless network implementation. Fifth-generation (5G) cellular networks emerge as a promising solution due to their low latency and high reliability. This article presents a study on the feasibility of implementing a licensed-spectrum 5G private network for process buses in substation automation systems (SAS) in accordance with IEC 61850. The simulation results indicate that using numerology 2 in the 3.7 GHz band (FR1) partially satisfies the latency constraints imposed by the IEC 61850 standard.

Leveraged by IoT and Industry 4.0 solutions, Wireless Sensor Networks (WSNs) have been proposed as an important alternative for large-scale monitoring applications. Such technology provides sensor nodes with the intelligent and autonomous ability to monitor large areas, create self-organizing structures, detect events and process massive data. In this context, data-driven schemes are increasingly needed. For this, some data clustering techniques (DCTs) are used to tackle common problems in WSNs; however, the vast majority of techniques do not consider the data monitored by the sensors to perform topological changes and provide better network structures. This work addresses an architecture for this type of application and evaluates the impact of different DCTs on network performance and the creation of priority node groups.

Wireless Sensor Networks (WSNs) based on the Long-Range radio modulation (LoRa) can use the LoRaWAN protocol as the medium access layer. However, this protocol only supports a single-hop star topology. As a consequence, devices can not use retransmissions along the network to extend their coverage area or to circumvent signal attenuation with distance, obstacles or interference from other radio sources. This paper proposes a multi-hop LoRaWAN wide-scale WSN based on a scheduled cluster-tree topology. This methodology can expand the spatial coverage of the network, decrease collisions, and improve overall network performance. A multi-hop cluster-tree topology eliminates the need for adjustments of LoRa radio parameters as an attempt to expand the single-hop coverage limitation. Simulation results show that the scheduled cluster-tree topology can scale the network coverage and significantly improve communication and energy consumption performances.

Wireless Sensor Networks (WSNs) have become a fundamental technology for implementing Internet of Things (IoT) solutions and supporting Industry 4.0 applications. This technology presents as main characteristics: high scalability, synchronized communication, and low power consumption. The network topological formation is a key factor in the design of WSNs, as the structure resulting from this process dictates the operation mode in which the network should handle such issues. For this, standards such as IEEE 802.15.4 and ZigBee have composed an adequate protocol stack, providing support for complex network topologies, such as cluster-tree. The objective of this work is to implement cluster-tree topology formation mechanisms driven by the data generated of sensor nodes, called the Bottom-Up Formation (BUF). The underlying idea is to select cluster-heads and build clusters following a bottom-up approach, aiming to define homogeneous tree branches in order to prioritize different data traffic. The results demonstrate that, compared to a state-of-the-art approach, the proposed mechanisms can reduce communication delays by up to 63%, achieve communication success rates of up to 99%, and extend the nodes’ lifetime.

LoRaWAN is a remarkable network protocol to support the deployment of low-power wide-area network applications for the Internet of Things. Its modulation scheme, LoRa, uses different transmission parameters to allow long-range bidirectional communication by trading-off range for Time on Air (ToA). The LoRaWAN specification suggests using an adaptive data rate (ADR) algorithm to assign transmission parameters to nodes dynamically. The ADR algorithm used by The Things Network, a global open network, selects transmission parameters for communication without disconnection while lowering ToA and energy consumption. However, its often optimistic link quality estimate drives the assignment of inadequate parameters, especially in lossy channels. More precise channel quality estimates would improve resource allocation at the cost of increased complexity at the network server (NS). Through simulations, we observe that we can use the ADR link margin parameter to compensate for inaccurate link quality estimates, providing better service to nodes and maintaining low levels of energy consumption. In this work, we propose a modification to ADR that allows the selection of the link margin at runtime, increasing the network performance without the need of any prior knowledge and with no increase in the NS computational complexity.

The use of adequate relay selection techniques is crucial to improve the behavior of cooperation based approaches in Wireless Sensor Networks (WSN). The Optimized Relay Selection Technique (ORST) is a relay selection technique that may be reduced to the application on classic set-covering problem (SCP) to WSN. The SCP seeks to find a minimum number of sets that contain all elements of all data sets. The SCP can be solved with different types of algorithms. This paper assesses the performance and quality of three different algorithms to solve the SCP generated by the previously proposed ORST technique, considering performance metrics relevant within WSNs context. The analysis was performed by simulation using the OMNeT++ tool and the WSN framework Castalia. The simulation results show that the branch and bound algorithm excels when compared to other state-of-the-art approaches.

The IEEE 802.15.4 and ZigBee applications are widely used specifications for the design of Wireless Sensor Networks (WSNs), Among the different available network topologies, cluster-tree networks are pointed out as the most suitable to implement large-scale WSNs, becoming an attractive solution for monitoring applications. However, cluster-tree networks may suffer from high end-to-end communication delay and also from network congestion. Thus, the selection of efficient network formation schemes and the definition of adequate communication structures are relevant research issues. In this context, this paper proposes an efficient mechanism to improve convergecast traffic in large-scale cluster-tree wireless sensor networks. The main idea combines a network formation process driven by the data generation characteristics of individual nodes and an efficient allocation scheme of the active periods, in order to improve typical convergecast message streams generated by the sensor nodes. Simulation results show that efficient network configuration approaches can significantly reduce end-to-end communication delays and decrease the overall network congestion.

Indoor Positioning Systems (IPS) constitutes a relevant research issue mainly due to the difficulties of employing Global Positioning System (GPS) technology in closed environments. Localization algorithms based on scene analysis technique, which map the environment signal levels at design time, present good results, being the main IEEE 802.11-based solution. In environments where this type of infrastructure is not available or the requirements for low-cost and power consumption limit the employment of such networks, other technologies should be used. Within this context, this work proposes a self-positioning system implemented in an IEEE 802.15.4 network. Considering a real scenario application, the proposed system presented relevant results, obtaining an accuracy of 0.6 m for the position estimation.

Cluster-tree topologies are commonly employed in large-scale Wireless Sensor Networks applications where nodes are randomly deployed. This topology presents several challenges related to connectivity and message schedulability. As a consequence, effective methods for network formation and operation are required. This work proposes a combination of methods of neighborhood discovery, network formation and message scheduling to deal with this problem. This proposal aims to build a flexible network, with better performance and is also able to adapt for different scenarios. Simulation results highlight significant improvements of the network performance, when compared to the use of LEACH protocol.

Topology formation in wireless sensor networks is usually done assuming just either the geographical proximity between nodes or the signal strength of communication. In this paper, a heuristic called DbCTF is proposed to guide the formation of cluster-tree networks, which also considers data clustering techniques. The use of DbCTF allows the setup of a data-based topology in the cluster-tree, and also the prioritisation of monitored regions in which relevant events may be occurring. The performance of DbCTF has been compared with a state-of-the-art algorithm, for the specific case of a classical WSN laboratory experiment. The simulation assessment revealed that the cluster-tree formed by DbCTF was able to reduce by more than 20% the average communication delay of message streams conveying critical data, and was also able to increase by more than 35% the average lifetime of the network.

Wireless Body Area Networks (WBANs) must comply with stringent communication requirements. One of these requirements is reliable data delivery. However, it is well-know that wireless networks operating in the same frequency range and using overlapping channels, tend to experience interferences that may compromise the network Quality of Service. This paper presents an experimental assessment of the interference of IEEE 802.11n networks upon IEEE 802.15.4-based WBANs, operating in the 2.4 GHz frequency band. A set of experimental tests were performed, in compliance with the IEEE 802.15.2 standard to assess the coexistence of IEEE 802.15.4 and IEEE 802.11n nodes, operating in overlapping and non-overlapping communication channels. The performed experimental tests considered different distances between the IEEE 802.11n access point and the IEEE 802.15.4 coordinator, as well as different communication channels, and different IEEE 802.11n network data rates. The experimental results highlight a strong interference between both networks, with a clear impact upon the communication reliability.

The use of Wireless Sensor Network (WSN) based technologies is an attractive solution for large-scale sensing applications (wide area deployment), such as environmental monitoring, precision agriculture and industrial automation. IEEE 802.15.4/ZigBee standards are the most used communication protocols for WSN technologies, where the clustertree topology is pointed out as a suitable topology to support the implementation of large-scale WSNs. These networks are usually scheduled to prioritise convergecast (upstream) traffic generated from sensor nodes toward the sink node. However, this scheduling pattern results in higher delays for control messages (downstream traffic). Within this context, this paper proposes a Hybrid Beacon Scheduling (Fast-HyBeS) scheme to enable the periodic reconfiguration of cluster-tree WSNs. The underlying idea is to periodically schedule a downstream opportunity window, to allow a faster dissemination of control messages. This opportunity window follows a top-down scheduling approach that prioritises the downstream traffic. Simulation results show that the use of Fast-HyBeS can significantly decrease the end-to-end communication delay for control messages, when compared to the use of static convergecast scheduling schemes. Moreover, the simulation results also highlight that the Fast-HyBeS has a negligible impact upon end-to-end communication delays of the monitoring traffic.

The use of Wireless Sensor Networks (WSNs) is considerably increasing, mainly due to their inherent low cost and wide range of applications. The formation of a WSN is driven by a request-based procedure that associates sensor nodes to a PAN (Personal Area Network) coordinator. In the IEEE 802.15.4 standard, the communication exchanges between a node willing to join the network and the PAN coordinator follows a CSMA/CA protocol. In this paper, we propose a set of specific improvements for the enhancement of the nodes joining procedure. The goal is to reduce the time spent in the association process, minimizing the time spent to deploy the network. A simulation assessment of the proposed set of improvements was performed using the OMNeT++/Castalia simulator, comparing their usage with the default mechanism defined by the IEEE 802.15.4 standard. The achieved results demonstrate that an adequate definition of the parameters of the CSMA/CA protocol significantly reduces the duration of the association procedure.

Wireless Sensor Networks (WSNs) arc susceptible to faults both in sensors and in communication. Information fusion techniques allow to extract precise information from a large amount of data. Detection, identification and treatment of outlier, in these techniques, is a key point. Outlier detection in WSNs is a challenge due to the low capacity of the nodes and low bandwidth of the network. This paper proposes a methodology that applies the clustering and lightweight statistics techniques for detection of outliers in WSNs. The assessment of the methodology involves a case study with temperature sensors in WSN nodes. The results show that this methodology is able to provide precise information, even in the presence of outliers.

The IEEE 802.15.4/ZigBee standards support the implementation of cluster-tree networks, which are a suitable topology to deploy wide-scale networks. In this type of topology, an important issue is the configuration of the superframe duration that is allocated to each of the network clusters. In this paper, we propose an allocation scheme for setting-up these superframe duration values. The proposed scheme allocates adequate duration values for each cluster coordinator, based on the message load originated from its child nodes (including child coordinators and its descendants). The target of the proposed allocation scheme is to improve the network throughput and to reduce network congestion and dropped messages. Its main advantages are: 1) to have a balanced allocation of network resources to the different clusters; 2) the message generation at the application layer does not need to be synchronised with the beacon arrival; and 3) the message periods do not need to be multiple of the beacon interval.

IEC 61850 is a communication standard for electrical Substation Automation Systems (SAS). It defines both the information model and services used for communication between Intelligent Electronic Devices (IEDs) in a substation. The adoption of this standard brings several advantages for the design and operation of substations. The abstract data models defined in IEC 61850 can be mapped upon application protocols, such as MMS, GOOSE or SMV. These protocols can run upon TCP/IP networks or upon specific high speed Ethernet LANs, in order to match the timing requirements associated to protective relaying mechanisms. For the specific case of GOOSE messages, the standard specifies the use of VLANs (Virtual LANs) with priority tagging (IEEE 802.1q) to implement separate virtual networks with the appropriate message priority levels, in order to ensure the specified response times. The lack of adequate simulation models that enable the response time assessment of both SMV and GOOSE messages is one of the shortcomings of available simulation tools. In this paper, we propose simulation models for the IEC 61850 communication standard, targeting application that use GOOSE and SMV messages. This simulation models has been built upon OMNeT++/INET. The simulation results obtained from a typical IEC 61850 communication scenario show the effectiveness of the developed models. Some of these results have been experimentally validated.

Energy consumption is a major problem in Wireless Sensor Networks (WSNs) since in most scenarios nodes operate on batteries with reduced size and low capacity. Battery lifetime estimation is therefore crucial to evaluate the network behavior over time. In addition, battery lifetime estimation is a major challenge since it depends on many factors, such as the duty cycle of supported applications and the intrinsic chemical reactions within the batteries. Several battery models have been proposed to deal with battery lifetime estimation. However, most of the available models address only high-capacity batteries. This paper discusses a method for extracting the parameters for the Kinetic Battery Model (KiBaM) used within WSN context. The target is to define a battery model that helps to estimate the lifetime of nodes using low-capacity batteries and which operate in a duty cycle scheme. Results show that KiBaM is an adequate model for WSNs since it presents low error when compared with experimental results using real batteries.

The use of wireless sensor networks (WSN) to support critical monitoring applications is becoming a relevant topic of interest. These networks allow a highly flexible approach to data monitoring and, consequently, a major breakthrough for several application domains, from industrial control applications to large building domotics and health care applications. One of the major impairments of using wireless networks to support critical monitoring applications is the electromagnetic noise, which may increase the packet loss ratio to unacceptable values. In this paper, we assess different techniques of cooperative communication and network coding that can be useful to mitigate the aforementioned problem. These techniques may be implemented in WSN nodes in conformance with the IEEE 802.15.4 standard, to reduce the impact of electromagnetic interferences upon the packet loss ratio. In this paper, we report an experimental assessment of the network coding and cooperative diversity techniques, where the network is subjected to a controlled electromagnetic interference inside of an anechoic chamber. The experimental results show that, by using these techniques, it is possible to increase the success rate of communication in typical electromagnetic noisy environments.

The IEEE 802.11 standard has been evolving over the past decade, introducing a set of new mechanisms at the MAC layer to improve the Quality of Service (QoS) provided to the communication. Among such improvements, we highlight the evolution from earlier DCF and PCF, until more recent EDCA and HCCA MAC layer mechanisms. In this paper we perform a simulation assessment of these four MAC mechanisms, evaluating their ability to support real-time (RT) communication. More specifically, we assess their ability to handle RT traffic in open communication environments composed of RT and non-RT stations operating in the same frequency channel and coverage area. The target of this paper is to highlight and understand the limitations of each mechanism when supporting RT communication. We show that for most of the situations, including less demanding scenarios, these mechanisms are not adequate to support RT traffic.

Many Wireless Sensor Network (WSN) applications operate autonomously in unreliable or inaccessible environments, precluding maintenance or human intervention. Redundant deployment schemes are usually considered in this scenario, making the network resilient to failure and environmental changes. Furthermore, sleep-scheduling techniques can also be applied, enabling redundant nodes to turn off their radios, while active nodes perform monitoring services. This paper investigates the behavior of the (m, k)-Gur Game approach. The main goal of the (m, k)-Gur Game is to provide an uniform network coverage for monitoring applications, with autonomic nodes performing a self-regulated choice between sending message to a base station or sleep until the next period. The proposal was evaluated using the OMNeT++ simulator tool under the MiXiM framework. Preliminary results shows that the (m, k)-Gur Game outperforms the traditional GurGame approach in terms of QoS provision and network coverage.

The use of cooperative diversity techniques and network coding concepts are promising solutions to improve the communication reliability in industrial Wireless Sensor Networks (WSNs). In this paper, we propose the NetCoDer scheme to address this problem, whose design is based in these concepts. The effectiveness of the NetCoDer scheme is evaluated through both an experimental setup with real WSN nodes and a simulation assessment, comparing its performance against state-of-the-art TDMA-based retransmission techniques.

In this paper we propose a novel approach, named Real-Time Alternative-Route Definition (RT-ARounD), to support real-time message streams over large-scale wireless sensor networks. Starting from a standard cluster-tree topology, where each cluster has active and inactive periods, the proposal selects a set of nodes to build a mesh topology which is used during the inactive periods of the respective clusters to transmit messages with real-time requirements. This new topology is built considering shortest path routes between source and sink nodes. In that way, the number of hops that a real-time message needs to transverse can be drastically reduced, thereby improving the real-time responsiveness of the overall network. Moreover, the use of the inactive period guarantees that the normal cluster-tree operation remains unaffected.

The IEEE 802.15.4 standard proposes a flexible communication solution for Low-Rate Wireless Personal Area Networks, including Wireless Sensor Networks. In these networks, the transmission of messages or the Guaranteed Time Slot allocation are coordinated by the traditional CSMA/CA scheme, which does not provide any additional traffic differentiation mechanism. In a previous work, we proposed an approach that assigns priorities to the messages based on the (m, k)-firm task model. This paper proposes, in a complementary way, an experimental assessment in order to define the best parameters for messages prioritization. The experimental assessment considers a realistic scenario in which a set of sensor nodes, implementing the proposed scheme works in the same coverage area of another set of nodes that does not belong to the same Wireless Sensor Networks infrastructure.

In several monitoring applications, such as those that can be found in industrial factory floor, it may be necessary to obtain an uniform sensing coverage, providing as much as possible the same coverage degree for the entire network area. The IEEE 802.15.4 has become an important standard in wireless sensor networks. However, the use of cluster-tree topology in these networks hampers a fair and uniform coverage in the sensing area. Clusters more distant from the base station are eventually adversely affected, with messages from its sensors delayed and discarded. In this paper, we propose a framework, entitled GLHOVE, whose goal is to make a trade-off between a minimum and uniform coverage area and the energy consumption of the network. The simulation results show an increase up to 20% of the fairness metric (w.r.t. messages received by base station).

In some Wireless Sensor Network (WSN) applications, it may be necessary to keep a large number of nodes sensing and transmitting data to a base station in order to have unbiased measurement values. Therefore, in addition to the traditional energy consumption issues, the spatial diversity of the monitored area is another relevant metric to evaluate the performance of a WSN. Nevertheless there is a clear trade-off between these two parameters, as keeping the sensors active all the time will deplete the nodes batteries and therefore will shorten the network lifetime. Fortunately, for the case of some applications it is possible to specify as a Quality of Service (QoS) parameter the number of periodically expected messages in the base station. Therefore, it will be possible to balance QoS against energy consumption. This paper proposes an approach called (m,k)-Gur Game that aims a trade-off between the expected QoS and the spatial coverage diversity. Simulation results show the effectiveness of the proposed approach.

In this paper is proposed a novel communication approach for implementation of parallel data fusion techniques in Wireless Sensor Networks. The approach is carried out by a distributed algorithm implemented in each network sensor node. In this approach, the network configures itself in order to adjust the number of messages sent periodically, establishing a tradeoff between the number of sent messages and the quality of data fusion (QoF). A prototype was implemented and experimental results show the effectiveness of this proposal.

The IEEE 802.15.4 standard provides a flexible communication approach for LR-WPAN networks. When active, the beacon-enabled mode allows real-time communication by adopting a GTS (Guaranteed Time Slot) mechanism. However, this mechanism supports only up to seven real-time communicating devices. Motivated by this problem, this paper proposes the use of a dynamic GTS scheduling approach based on the (m, k)-firm task model, to deal with the GTS starvation problem. The proposed approach ensures that, for each admitted message stream Siat least m messages will be transmitted within each window of k consecutive deadlines. The effectiveness of the proposed scheduling approach is demonstrated by a set of simulation and experimental results. The proposed approach is fully compatible with the IEEE 802.15.4 standard.

Mobile agents have been proposed as a means to address two important issues in the design of Wireless Sensor Networks (WSN): the need for reprogramming the network and decreasing energy expenditure. However, few mobile agent systems have been developed for WSN so far. In this paper we describe MASPOT, a mobile agent system for Sun SPOT, a WSN platform developed by Sun Microsystems. MASPOT provides a solution to the issues above and extends the range of Sun SPOT applications. To the best of our knowledge, MASPOT is the only Java-based mobile agent system for WSN that currently supports code migration. We describe the system and present the results of an experiment to evaluate the amount of energy spent during agent migration. It showed that migration spends around 0.03% of the nodes battery energy. Additionally, MASPOT uses only around 1.5% of the available flash memory of Sun SPOT nodes.

Algorithms to determine the itinerary of agents are fundamental in the context of distributed applications based on mobile agents with timing requirements. To establish an agent's itinerary it is necessary to consider the trade-offs between achieving

Wireless Sensor Networks (WSNs) can be used to monitor hazardous and inaccessible areas. The WSN is composed of several nodes each provided with its separated power supply, e.g. battery. Working in hardly accessible places it is preferable to assure the adoption of the minimum transmission power in order to prolong as much as possible the WSN’’s lifetime. Though, we have to keep in mind that the reliability of the data transmitted represents a crucial requirement. Therefore, power optimization and reliability have become the most important concerns when dealing with modern systems based on WSN. In this context, we propose to evaluate the effectiveness of a Transmission Power Self-Optimization (TPSO) technique for WSNs in an Electromagnetic Interference (EMI) Environment. The TPSO technique consists of an algorithm able to guarantee an equally high Quality of Service (QoS), concentrating on the WSN’’s Efficiency (Ef), while optimizing the transmission power necessary for data communication. Thus, the main idea behind our approach is to reach a trade-off between Ef and energy consumption in an environment with inherent noise.

Software applications use hash tables for many different purposes. Hash tables have an excellent average-case behavior but, in the worst-case, it degrades to something like a chained list. Because of that, the use of hash tables in real-time systems is not usual, since those systems may be required to guarantee deadlines. This paper discusses the use of hash table in real-time systems, considering that when the probability of an undesirable behavior is low enough, it can be ignored. It also compares approaches simple and 2-choice for the table design.

IEEE 802.15.4/Zigbee is one of the most widespread Wireless Sensor Network technologies. It may work either in beacon-enabled mode or in beaconless mode. When operating in beacon-enabled mode, it divides the superframe in sixteen equally-sized time slots, where the request for slot allocation is achieved through a CSMA/CA approach. This allocation method does not allow the provision of any service differentiation scheme, which is required for the transfer of time constrained messages. This paper proposes a QoS provision approach with minimal changes to existing protocols. Our approach improves the CSMA/CA algorithm by assigning decentralized priorities based on the (m,k)-firm task model. In this paper, a set of experimental results is presented and compared with the traditional approach currently offered by the standard. This set of experiments highlight the promising behavior of the proposed approach, when dealing with high network load scenarios.

Networked control systems (NCSs) are a very interesting solution to several control problems, and the definition of metrics and procedures for the design of more efficient NCSs is an open research field. This paper analyzes two evaluation metrics currently available: the quality-of-control and the jitter margin. This analysis will be used in further studies at the Federal University of Santa Catarina, Brazil, to determine a design procedure for NCSs.

Wireless sensor networks (WSN) are being targeted for use in applications like security, resources monitoring and factory automation. However, the reduced available resources raise a lot of technical challenges. Self-organization in WSN is a desirable characteristic that can be achieved by means of data fusion techniques when delivering reliable data to users. In this paper it is proposed a genetic machine learning algorithm (GMLA) approach that makes a trade-off between quality of information and communication efficiency. GMLA is based on genetic algorithms and it can adapt itself dynamically to environment modifications. The main target of the proposed approach is to achieve self-organization in a WSN application with data fusion. Simulations demonstrate that the proposed approach can optimize communication efficiency in a dense WSN.

In this work we propose an end-to-end deadline missing prediction mechanism called Available Remaining Slack (ARS) for distributed threads. Simulations show that the proposed prediction mechanism presents good results for improving the overall performance and availability of distributed real-time systems.

This paper discusses the use of mobile agents with timing requirements in a distributed system. The goal of this paper is to propose and to evaluate heuristics for imprecise mobile agents that should execute a mission while meeting firm deadlines. These heuristics are used to determine the itinerary of the mobile agents. They choose a behavior considering previous benefits collected by the mobile agent in past executions. The agent uses adaptation at the departure. Once chosen the behavior for a particular mission, the agent keeps this behavior until the end of the mission. In order to choose the behavior it is used conditional probability based on the characteristics of the environment and on the last events. The algorithms proposed here were evaluated through simulations.

In some applications, as part of a mobile agent mission, there may be the necessity of meeting a firm end-to-end deadline, although with some itinerary flexibility due to optional resources. This paper proposes an execution model based on the concept

Distributed real-time threads are schedulable entities with an end-to-end deadline that traverse nodes, carrying their scheduling context. In each node, the thread will be locally scheduled and predictions about deadline missing allow that actions are carried out to improve system performance. This paper presents a task model and deadline partitioning algorithms that consider the possibility of a distributed thread to follow different paths. The future execution flow of the distributed thread is only probabilistic known before its execution. End-to-end deadline missing prediction mechanisms can be carried out through definition of estimated local deadlines. Simulations show that the proposed prediction mechanism presents good results in overloaded systems.

This paper describes an extension to the component-based programming model to support real-time dynamic guarantee for distributed applications. The extended model aims to include an acceptance tests to component-based servers at bind time. We present the mapping of our model to the CORBA Component Model, the architecture to support the dynamic guarantee in component-based middleware, the implementation of this architecture in CIAO (Component Integrated ACE ORB) and the result of experiments run to evaluate the cost of the mechanisms used

In some applications, as part of a mobile agent mission, there may be the necessity of meeting a firm end-to-end deadline, although with some itinerary flexibility due to optional resources. In this paper it is considered an execution model where agents do not previously know their itineraries. The objective is to propose and to evaluate heuristics to be used by pairs of imprecise mobile agents that must accomplish a mission within a firm deadline.

The Web services architecture came as answers to the search for interoperability among applications. There has been a growing interest in deploying on the Internet applications with high availability and reliability requirements. However, the technologies associated with this architecture still do not deliver adequate support to this requirement. The model proposed in this article is located in this context and provides a new layer of software that acts as a proxy between client requests and service delivery by providers. The main objective is to ensure client transparent fault tolerance by means of the active replication technique. This model supports the following faults: value, omission and stops. This paper describes the features and outcomes obtained through the implementation of this model.

In this paper we propose a system architecture that supports end-to-end scheduling of the distributed real-time thread abstraction. The real-time specification for Java (RTSJ) is used for the implementation of distributed real-time threads. By using simulations, we conclude that the proposed architecture is flexible enough to accommodate different scheduling algorithms

This work describes the proposal of a set of mechanisms to be applied in distributed component-based systems to allow the development of real-time applications capable of offering dynamic guarantee for clients. The proposal aims to make the application server able to provide service completion according to all clients imposed timing constraints or the immediate request rejection. To implement these mechanisms, we use an acceptance test at bind time to filter services requests. The acceptance test determines which service request will be executed, based on the system capacity and current load, providing therefore, dynamic guarantee for all the provided services

This paper analyzes the importance of differentiated service implementation in current Web servers, within the context of new Internet applications. An innovative approach of resource management is presented, which is carried out using the proportional cumulative value attribution (PCV) heuristic. This heuristic acts through two policies which, in response to requests, simultaneously sort the requests according to dynamically assigned priorities; and select different versions of Web pages.

CORBA is an emerging middleware infrastructure with open standardization that is receiving a good acceptance since it allows easier programming of distributed objects. CORBA is being extended through the specification of interfaces and necessary abstractions to support applications with real time constraints. These new abstractions will enable a variety of programming models for real time applications. The paper presents an adaptive programming model for distributed real time applications using CORBA concepts. The model combines the time polymorphic invocation technique with the (m,k)-firm guarantee.