Orchestration of e-learning services for automatic evaluation of programming exercises

Managing programming exercises require several heterogeneous systems such as evaluation engines, learning objects repositories and exercise resolution environments. The coordination of networks of such disparate systems is rather complex. These tools would be too specific to incorporate in an e-Learning platform. Even if they could be provided as pluggable components, the burden of maintaining them would be prohibitive to institutions with few courses in those domains. This work presents a standard based approach for the coordination of a network of e-Learning systems participating on the automatic evaluation of programming exercises. The proposed approach uses a pivot component to orchestrate the interaction among all the systems using communication standards. This approach was validated through its effective use on classroom and we present some preliminary results.

The cross crypto scheme cipher integration for securing SCADA component communication

Critical Infrastructures became more vulnerable to attacks from adversaries as SCADA systems become connected to the Internet. The open standards for SCADA Communications make it very easy for attackers to gain in-depth knowledge about the working and operations of SCADA networks. A number of Intenrnet SCADA security issues were raised that have compromised the authenticity, confidentiality, integrity and non-repudiation of information transfer between SCADA Components. This paper presents an integration of the Cross Crypto Scheme Cipher to secure communications for SCADA components. The proposed scheme integrates both the best features of symmetric and asymmetric encryptiontechniques. It also utilizes the MD5 hashing algorithm to ensure the integrity of information being transmitted.

IEEE 802.15.4 for wireless sensor networks: a technical overview

Low-rate low-power consumption and low-cost communication are the key points that lead to the specification of the IEEE 802.15.4 standard. This paper overviews the technical features of the physical layer and the medium access control sublayer mechanisms of the IEEE 802.15.4 protocol that are most relevant for wireless sensor network applications. We also discuss the ability of IEEE 802.15.4 to fulfil the requirements of wireless sensor network applications.

Lower protocol layers for wireless sensor networks: a survey

Wireless Sensor Networks (WSNs) have been attracting increasing interests in the development of a new generation of embedded systems with great potential for many applications such as surveillance, environment monitoring, emergency medical response and home automation. However, the communication paradigms in Wireless Sensor Networks differ from the ones attributed to traditional wireless networks, triggering the need for new communication protocols and mechanisms. In this Technical Report, we present a survey on communication protocols for WSNs with a particular emphasis on the lower protocol layers. We give a particular focus to the MAC (Medium Access Control) sub-layer, since it has a prominent influence on some relevant requirements that must be satisfied by WSN protocols, such as energy consumption, time performance and scalability. We overview some relevant MAC protocol solutions and discuss how they tackle the trade-off between the referred requirements.

Supporting conceptualisation processes in collaborative networks: a case study on an R&D project

The development of new products or processes involves the creation, re-creation and integration of conceptual models from the related scientific and technical domains. Particularly, in the context of collaborative networks of organisations (CNO) (e.g. a multi-partner, international project) such developments can be seriously hindered by conceptual misunderstandings and misalignments, resulting from participants with different backgrounds or organisational cultures, for example. The research described in this article addresses this problem by proposing a method and the tools to support the collaborative development of shared conceptualisations in the context of a collaborative network of organisations. The theoretical model is based on a socio-semantic perspective, while the method is inspired by the conceptual integration theory from the cognitive semantics field. The modelling environment is built upon a semantic wiki platform. The majority of the article is devoted to developing an informal ontology in the context of a European R&D project, studied using action research. The case study results validated the logical structure of the method and showed the utility of the method.

Characterizing the timing behaviour of power-line communication by means of simulation

Although power-line communication (PLC) is not a new technology, its use to support communication with timing requirements is still the focus of ongoing research. Recently, a new infrastructure was presented, intended for communication using power lines from a central location to geographically dispersed nodes using inexpensive devices. This new infrastructure uses a two-level hierarchical power-line system, together with an IP-based network. Within this infrastructure, in order to provide end-toend communication through the two levels of the powerline system, it is necessary to fully understand the behaviour of the underlying network layers. The masterslave behaviour of the PLC MAC, together with the inherent dynamic topology of power-line networks are important issues that must be fully characterised. Therefore, in this paper we present a simulation model which is being used to study and characterise the behaviour of power-line communication.

Industrial multimedia over factory-floor networks

In this paper we describe a real-time industrial communication network able to support both controlrelated and multimedia traffic. The industrial communication network is based on the PROFIBUS standard, with multimedia capabilities being provided by an adequate integration of TCP/IP protocols into the PROFIBUS stack. From the operational point of view the integration of TCP/IP into PROFIBUS is by itself a challenge, since the master-slave nature of the PROFIBUS MAC makes complex the implementation of the symmetry inherent to IP communications. From the timeliness point of view the challenge is two folded. On one hand the multimedia traffic should not interfere with the timing requirements of the "native" control-related PROFIBUS traffic (typically hard real-time). On the other hand multimedia traffic requires certain levels of quality-of-service to be attained. In this paper we provide a methodology that enables fulfilling the timing requirements for both types of traffic in these real-time industrial LAN. Moreover, we describe suitable algorithms for the scheduling support of concurrent multimedia streams.

Supporting internet protocols in master-slave fieldbus networks

In this paper we describe how to integrate Internet Protocols (IP) into a typical hierarchical master-slave fieldbus network, supporting a logical ring token passing mechanism between master stations. The integration of the TCP/IP protocols in the fieldbus protocol rises a number of issues that must be addressed properly. In this paper we particularly address the issues related to the conveyance of IP fragments in fieldbus frames (fragmentation/de-fragmentation) and on how to support the symmetry inherent to the TCP/IP protocols in fieldbus slaves, which lack communication initiative.

Setting target rotation time in PROFIBUS based real-time distributed applications

In this paper, we analyse the ability of Profibus fieldbus to cope with the real-time requirements of a Distributed Computer Control System (DCCS), where messages associated to discrete events must be made available within a maximum bound time. Our methodology is based on the knowledge of real-time traffic characteristics, setting the network parameters in order to cope with timing requirements. Since non-real-time traffic characteristics are usually unknown at the design stage, we consider an operational profile where, constraining non-real-time traffic at the application level, we assure that realtime requirements are met.

Queuing and routing in a hierarchical powerline communication system

Although power-line communication (PLC) is not a new technology, its use to support data communication with timing requirements is still the focus of ongoing research. A new infrastructure intended for communication using power lines from a central location to dispersed nodes using inexpensive devices was presented recently. This new infrastructure uses a two-level hierarchical power-line system, together with an IP-based network. Due to the master-slave behaviour of the PLC medium access, together with the inherent dynamic topology of power-line networks, a mechanism to provide end-to-end communication through the two levels of the power-line system must be provided. In this paper we introduce the architecture of the PLC protocol layer that is being implemented for this end.

A power line communication stack for metering, SCADA and large-scale domotic applications

This paper describes the communication stack of the REMPLI system: a structure using power-lines and IPbased networks for communication, for data acquisition and control of energy distribution and consumption. It is furthermore prepared to use alternative communication media like GSM or analog modem connections. The REMPLI system provides communication service for existing applications, namely automated meter reading, energy billing and domotic applications. The communication stack, consisting of physical, network, transport, and application layer is described as well as the communication services provided by the system. We show how the peculiarities of the power-line communication influence the design of the communication stack, by introducing requirements to efficiently use the limited bandwidth, optimize traffic and implement fair use of the communication medium for the extensive communication partners.

Evaluating the duration of message transactions in broadcast wired/wireless fieldbus networks

Determining the response time of message transactions is one of the major concerns in the design of any distributed computer-controlled system. Such response time is mainly dependent on the medium access delay, the message length and the transmission delay. While the medium access delay in fieldbus networks has been thoroughly studied in the last few years, the transmission delay has been almost ignored as it is considered that it can be neglected when compared to the length of the message itself. Nevertheless, this assumption is no longer valid when considering the case of hybrid wired/wireless fieldbus networks, where the transmission delay through a series of different mediums can be several orders of magnitude longer than the length of the message itself. In this paper, we show how to compute the duration of message transactions in hybrid wired/wireless fieldbus networks. This duration is mainly dependent on the duration of the request and response frames and on the number and type of physical mediums that the frames must cross between initiator and responder. A case study of a hybrid wired/wireless fieldbus network is also presented, where it becomes clear the interest of the proposed approach

An architecture for reliable distributed computer-controlled systems

In Distributed Computer-Controlled Systems (DCCS), both real-time and reliability requirements are of major concern. Architectures for DCCS must be designed considering the integration of processing nodes and the underlying communication infrastructure. Such integration must be provided by appropriate software support services. In this paper, an architecture for DCCS is presented, its structure is outlined, and the services provided by the support software are presented. These are considered in order to guarantee the real-time and reliability requirements placed by current and future systems.

Programming atomic multicasts in CAN

In Distributed Computer-Controlled Systems (DCCS), a special emphasis must be given to the communication infrastructure, which must provide timely and reliable communication services. CAN networks are usually suitable to support small-scale DCCS. However, they are known to present some reliability problems, which can lead to an unreliable behaviour of the supported applications. In this paper, an atomic multicast protocol for CAN networks is proposed. This protocol explores the CAN synchronous properties, providing a timely and reliable service to the supported applications. The implementation of such protocol in Ada, on top of the Ada version of Real-Time Linux is presented, which is used to demonstrate the advantages and disadvantages of the platform to support reliable communications in DCCS.

Using WorldFIP networks to support periodic and sporadic real-time traffic

In this paper we address the ability of WorldFIP to cope with the real-time requirements of distributed computer-controlled systems (DCCS). Typical DCCS include process variables that must be transferred between network devices both in a periodic and sporadic (aperiodic) basis. The WorldFIP protocol is designed to support both types of traffic. WorldFIP can easily guarantee the timing requirements for the periodic traffic. However, for the aperiodic traffic more complex analysis must be made in order to guarantee its timing requirements. This paper describes work that is being carried out to extend previous relevant work, in order to include the actual schedule for the periodic traffic in the worst-case response time analysis of sporadic traffic in WorldFIP networks