Abstract: This paper reviews the work performed under the
European ESPRIT project DO_ALL (Digital OpticAL Logic
modules) spanning from advanced devices (semiconductor optical
amplifiers) to all-optical modules (laser sources and gates) and
from optical signal processing subsystems (packet clock recovery,
optical write/store memory, and linear feedback shift register) to
their integration in the application level for the demonstration of
nontrivial logic functionality (all-optical bit-error-rate tester and
a 2 2 exchange–bypass switch). The successful accomplishment
of the project¢s goals has opened the road for the implementation
of more complex ultra-high-speed all-optical signal processing
circuits that are key elements for the realization of all-optical
packet switching networks.
Abstract: Raising awareness among young people and changing their behaviour and habits concerning energy usage is key to achieving sustained energy saving. Additionally, young people are very sensitive to environmental protection so raising awareness among children is much easier than with any other group of citizens. This work examines ways to create an innovative Information & Communication Technologies (ICT) ecosystem (including web-based, mobile, social and sensing elements) tailored specifically for school environments, taking into account both the users (faculty, staff, students, parents) and school buildings, thus motivating and supporting young citizens¢ behavioural change to achieve greater energy efficiency. A mixture of open-source IoT hardware and proprietary platforms on the infrastructure level, are currently being utilized for monitoring a fleet of 18 educational buildings across 3 countries, comprising over 700 IoT monitoring points. Hereon presented is the system¢s high-level architecture, as well as several aspects of its implementation, related to the application domain of educational building monitoring and energy efficiency. The system is developed based on open-source technologies and services in order to make it capable of providing open IT-infrastructure and support from different commercial hardware/sensor vendors as well as open-source solutions. The system presented can be used to develop and offer new app-based solutions that can be used either for educational purposes or for managing the energy efficiency of the building. The system is replicable and adaptable to settings that may be different than the scenarios envisioned here (e.g., targeting different climate zones), different IT infrastructures and can be easily extended to accommodate integration with other systems. The overall performance of the system is evaluated in real-world environment in terms of scalability, responsiveness and simplicity.
Abstract: We present the conceptual basis and the initial planning for an opensource management architecture for wireless sensor networks (WSN). Although there is an abundance of opensource tools serving the administrative needs of WSN deployments, there is a lack of tools or platforms for high level integrated WSN management. This is because of a variety of factors, including the lack of opensource management tools, the immaturity of tools that offer manageability for WSNs, the limited high level management capabilities of sensor devices and architectures, and the lack of standardization. The current work is, to our knowledge, the first effort to conceptualize, formalize and design a remote, integrated management platform for the support of WSN research laboratories. The platform is based on the integration and extension of two innovative platforms: jWebDust, a WSN operation and management platform, and OpenRSM, an opensource integrated remote systems and network management platform. The proposed system architecture can support several levels of integration (infrastructure management, functionality integration, firmware management), corresponding to different use-cases and application settings.
Abstract: The Greek School Network (GSN) has developed and put into production a number of e-learning services, including synchronous and asynchronous tele-education, electronic class management, blogs, video-on-demand, podcasts and multimedia libraries. These new services complement established and accepted e-learning services, such as teleconferencing, user wikis, forums, email, electronic publishing, and e-magazines. This report presents the most prominent digital e-learning services offered by GSN, with emphasis on the asynchronous tele-education service, which is presented in detail. Its implementation platform, the Moodle course management system, is compared against well-known asynchronous opensource tele-education platforms such as COSE, Claroline, Fle3, ILIAS, Manhattan, KEWL, Comentor, e-Class and Eledge. The evaluation of the asynchronous tele-education platforms is based on detailed comparisons of their characteristics and of the methodology they adopt in order to deliver educational services. The comparison is based on evaluation criteria derived from the documented experiences of research institutes and educational bodies and also from the experience of GSN itself. The paper concludes with the presentation of an extension to Moodle for implementing communities of practice (CoPs) that facilitate the creation and delivery of electronic educational open content for teachers in a synergetic manner.
Abstract: This paper presents ongoing work on using data mining clustering to support the evaluation of software
systems' maintainability. As input for our analysis we employ software measurement data extracted from
Java source code. We propose a two-steps clustering process which facilitates the assessment of a system's
maintainability at rst, and subsequently an in-cluster analysis in order to study the evolution of each
cluster as the system's versions pass by. The process is evaluated on Apache Geronimo, a J2EE 1.4 opensource Application Server. The evaluation involves analyzing several versions of this software system in
order to assess its evolution and maintainability over time. The paper concludes with directions for future
work.
Abstract: This work proposes a methodology for source code quality and static behaviour evaluation of a software
system, based on the standard ISO/IEC-9126. It uses elements automatically derived from source code
enhanced with expert knowledge, in the form of quality characteristic rankings, allowing software
engineers to assign weights to source code attributes. It is flexible in terms of the set of metrics and
source code attributes employed, even in terms of the ISO/IEC-9126 characteristics to be assessed. We
applied the methodology to two case studies, involving five opensource and one proprietary system.
Results demonstrated that the methodology can capture software quality trends and express expert
perceptions concerning system quality in a quantitative and systematic manner
Abstract: The Greek School Network (GSN) is the nationwide network that connects all units of primary and secondary education in Greece. GSN offers a significant set of diverse services to more than 15.000 schools and administrative units, and more than 60.000 teachers, placing GSN second in infrastructure size nationwide. GSN has relied on the emerging power of opensource software to build cutting-edge services capable of covering internal administrative and monitoring needs, end user demands, and, foremost, modern pedagogical requirements for tools and services. GSN provides a wide set of advanced services, varying from web mail to virtual classrooms and synchronous/asynchronous tele-education. This paper presents an evaluation of GSN opensource services based on the opinions of users who use GSN for educational purposes, and on usage and traffic measurement statistics. The paper reaches the conclusion that opensource software provides a sound technological platform that meets the needs for cutting edge educational services deployment, and innovative, competitive software production for educational networks.
Abstract: Wireless sensor networks are a recently introduced category of ad hoc computer networks, which are comprised by nodes of small size and limited computing and energy resources. Such nodes are able of measuring physical properties such as temperature, humidity, etc., wireless communication between each other and in some cases interaction with their surrounding environments (through the use of electromechanical parts).
As these networks have begun to be widely available (in terms of cost and commercial hardware availability), their field of application and philosophy of use is constantly evolving. We have numerous examples of their applications, ranging from monitoring the biodiversity of a specific outdoor area to structural health monitoring of bridges, and also networks ranging from few tens of nodes to even thousands of nodes.
In this PhD thesis we investigated the following basic research lines related to wireless sensor networks:
a) their simulation,
b) the development of data propagation protocols suited to such networks and their evaluation through simulation,
c) the modelling of ``hostile'' circumstances (obstacles) during their operation and evaluation of their impact through simulation,
d) the development of a sensor network management application.
Regarding simulation, we initially placed an emphasis to issues such as the effective simulation of networks of several thousands of nodes, and in that respect we developed a network simulator (simDust), which is extendable through the addition of new data propagation protocols and visualization capabilities. This simulator was used to evaluate the performance of a number of characteristic data propagation protocols for wireless sensor networks. Furthermore, we developed a new protocol (VRTP) and evaluated its performance against other similar protocols. Our studies show that the new protocol, that uses dynamic changes of the transmission range of the network nodes, performs better in certain cases than other related protocols, especially in networks containing obstacles and in the case of non-homogeneous placement of nodes.
Moreover, we emphasized on the addition of ``realistic'' conditions to the simulation of such protocols, that have an adversarial effect on their operation. Our goal was to introduce a model for obstacles that adds little computational overhead to a simulator, and also study the effect of the inclusion of such a model on data propagation protocols that use geographic information (absolute or relative). Such protocols are relatively sensitive to dynamic topology changes and network conditions. Through our experiments, we show that the inclusion of obstacles during simulation can have a significant effect on these protocols.
Finally, regarding applications, we initially proposed an architecture (WebDust/ShareSense), for the management of such networks, that would provide basic capabilities of managing such networks and developing applications above it. Features that set it apart are the capability of managing multiple heterogeneous sensor networks, openess, the use of a peer-to-peer architecture for the interconnection of multiple sensor network. A large part of the proposed architecture was implemented, while the overall architecture was extended to also include additional visualization capabilities.
Abstract: Counting items in a distributed system, and estimating the cardinality of multisets in particular,
is important for a large variety of applications and a fundamental building block for emerging Internet-scale information systems. Examples of such applications range from optimizing query access plans in peer-to-peer data sharing, to computing the significance (rank/score) of data items in distributed information retrieval. The general formal problem addressed in this article is computing the network-wide distinct number of items with some property (e.g., distinct files with file name
containing “spiderman”) where each node in the network holds an arbitrary subset, possibly overlapping the subsets of other nodes. The key requirements that a viable approach must satisfy are:
(1) scalability towards very large network size, (2) efficiency regarding messaging overhead, (3) load
balance of storage and access, (4) accuracy of the cardinality estimation, and (5) simplicity and easy
integration in applications. This article contributes the DHS (Distributed Hash Sketches) method
for this problem setting: a distributed, scalable, efficient, and accurate multiset cardinality estimator.
DHSis based on hash sketches for probabilistic counting, but distributes the bits of each counter
across network nodes in a judicious manner based on principles of Distributed Hash Tables, paying
careful attention to fast access and aggregation as well as update costs. The article discusses various
design choices, exhibiting tunable trade-offs between estimation accuracy, hop-count efficiency, and
load distribution fairness. We further contribute a full-fledged, publicly available, open-source implementation of all our methods, and a comprehensive experimental evaluation for various settings.
Abstract: As the Internet of Things (IOT) arises, the use of
low-end devices on a daily basis increases. The wireless nature
of communication that these devices provide raises security and
privacy issues. For protecting a user’s privacy, cryptography
offers the tool of zero knowledge proofs (ZKP). In this
paper, we study well-established ZKP protocols based on the
discrete logarithm problem and we adapt them to the Elliptic
Curve Cryptography (ECC) setting, which consists an ideal
candidate for embedded implementations. Then, we implement
the proposed protocols on Wiselib, a generic and opensource
algorithmic library. For the first time, we present a thorough
evaluation of the protocols on two popular hardware platforms
equipped with low end microcontrollers (Jennic JN5139, TI
MSP430) and 802.15.4 RF transceivers, in terms of code size,
execution time, message size and energy requirements. This
work’s results can be used from developers who wish to achieve
certain levels of privacy in their applications.
Abstract: The promises inherent in users coming together to form data
sharing network communities, bring to the foreground new problems formulated
over such dynamic, ever growing, computing, storage, and networking
infrastructures. A key open challenge is to harness these highly
distributed resources toward the development of an ultra scalable, efficient
search engine. From a technical viewpoint, any acceptable solution
must fully exploit all available resources dictating the removal of any
centralized points of control, which can also readily lead to performance
bottlenecks and reliability/availability problems. Equally importantly,
however, a highly distributed solution can also facilitate pluralism in informing
users about internet content, which is crucial in order to preclude
the formation of information-resource monopolies and the biased visibility
of content from economically-powerful sources. To meet these challenges,
the work described here puts forward MINERVA{\^a}{\"i}¿½{\"i}¿½, a novel search
engine architecture, designed for scalability and efficiency. MINERVA{\^a}{\"i}¿½{\"i}¿½
encompasses a suite of novel algorithms, including algorithms for creating
data networks of interest, placing data on network nodes, load balancing,
top-k algorithms for retrieving data at query time, and replication algorithms
for expediting top-k query processing. We have implemented the
proposed architecture and we report on our extensive experiments with
real-world, web-crawled, and synthetic data and queries, showcasing the
scalability and efficiency traits of MINERVA{\^a}{\"i}¿½{\"i}¿½.
Abstract: Managing corporate Information Technology (IT) environment becomes increasingly complex as server logic architecture becomes distributed and the number of manageable entities increases. At the same time, the opensource community has not yet produced a reliable systems and network management solution, even though there are opensource initiatives specializing in individual fields of remote management. This paper presents OpenRSM, an integrated remote management system created by integrating individual opensource initiatives and augmenting them to support additional functionality so that a lightweight integrated systems and network management solution is produced.
Abstract: A collection of pervasive street games is presented in this paper, that constitute a new social form of play taking place in public spaces, such as city parks, public spaces and streets. The main characteristic of these games is the ability to scale to a large number of players (in some cases involving more than 40 players) and can engage players located simultaneously in dispersed areas. Players interact with each other using a wide range of hardware devices that are either generic (such as smart phones) or specific (such as wireless sensor devices). We discuss a set of fundamental issues related to game design emphasizing on the one hand the interaction of the players with the ubiquitous computing environment and on the other hand the embedding of the game rules within the environment. The games are developed using opensource technologies and evaluated in a series of events such as the Athens Plaython 2012 festival. The feedback received from the players indicates that this new form of gaming is indeed very promising.
Abstract: Elliptic Curve Cryptography (ECC) is one of the
most promising alternatives to conventional public
key cryptography, such as RSA and ElGamal, since
it employs keys of smaller sizes for the same level
of cryptographic strength. Smaller key sizes imply
smaller hardware units for performing the arithmetic
operations required by cryptographic protocols and,
thus, ECC is an ideal candidate for implementation
in embedded systems where the major computational
resources (speed and storage) are limited.
In this paper we present a port, written in ANSI C
for maximum portability, of an opensource ECCbased
cryptographic library (ECC-LIB) to ATMEL¢s
AT76C520 802.11 WLAN Access Point. One of the
major features of this port, not found in similar ports,
is that it supports Complex Multiplication (CM) for
the construction of Elliptic Curves with good security
properties. We present some experimental results that
demonstrate that the port is efficient and can lead to generic embedded systems with robust ECC-based
cryptographic protocols using cryptographically strong
ECCs generated with CM. As an application of the
ported library, an EC Diffie-Hellman key exchange
protocol is developed as an alternative of the 4-way
key handshake protocol of the 802.11 protocol.
Abstract: Efficient query processing in traditional database
management systems relies on statistics on base data. For centralized systems, there is a rich body of research results on such statistics, from simple aggregates to more elaborate synopses such as sketches and histograms. For Internet-scale distributed systems, on the other hand, statisticsmanagement still poses major challenges. With the work in this paper we aim to endow peer-to-peer data management over structured
overlays with the power associated with such statistical information, with emphasis on meeting the scalability challenge.
To this end, we first contribute efficient, accurate, and decentralized algorithms that can compute key aggregates such as Count, CountDistinct, Sum, and Average. We show how to construct several types of histograms, such as simple Equi-Width, Average Shifted Equi-Width, and Equi-Depth histograms. We present a full-fledged open-source implementation
of these tools for distributed statistical synopses,
and report on a comprehensive experimental performance evaluation, evaluating our contributions in terms of efficiency, accuracy, and scalability.
Abstract: We present the conceptual basis and the initial planning for an opensource management architecture for wireless sensor networks (WSN). Although
there is an abundance of opensource tools serving the administrative needs of
WSN deployments, there is a lack of tools or platforms for high level integrated
WSN management. The current work is, to our knowledge, the first effort to
conceptualize and design a remote, integrated management platform for the
support of WSN research laboratories. The platform is based on the integration
and extension of two innovative platforms: jWebDust, a WSN operation and
management platform, and OpenRSM, an opensource integrated remote
systems and network management platform. The proposed system architecture
can support several levels of integration in order to cover to multiple,
qualitatively differentiated use-cases.
Abstract: The Greek School Network (GSN) is a closed nationwide
educational network that offers advanced telematic and
networking services to all primary/secondary education schools
and administration offices in Greece. The primary objective of
GSN is the provisioning of a network infrastructure for the interconnection
of school PC laboratories so that modern educational
methods and pedagogical models can be applied to the school
community. GSN has scaled in size, has reached maturity, and
is currently delivering a wide range of network and telematic
services to its users. The emerging power of open-source software
provides a sound technological basis for building cutting-edge
services, capable of meeting internal administrative and monitoring
needs, and modern pedagogical requirements for tools and
services. The current paper presents an overview of GSN and an
evaluation of its services based on the opinions of its users, and on
service utilization and traffic measurement statistics. The paper
reaches the conclusion that open-source solutions provide a sound
technological platform that can cover, to a great extent, the needs
for advanced educational services of the school community.
Abstract: For the Internet of Things to finally become a reality, obstacles on different levels need to be overcome. This is especially true for the upcoming challenge of leaving the domain of technical experts and scientists. Devices need to connect to the Internet and be able to offer services. They have to announce and describe these services in machine understandable ways so that user-facing systems are able to find and utilize them. They have to learn about their physical surroundings, so that they can serve sensing or acting purposes without explicit configuration or programming. Finally, it must be possible to include IoT devices in complex systems that combine local and remote data, from different sources, in novel and surprising ways.
We show how all of that is possible today. Our solution uses open standards and state-of-the art protocols to achieve this. It is based on 6LowPAN and CoAP for the communications part, semantic web technologies for meaningful data exchange, autonomous sensor correlation to learn about the environment, and software built around the Linked Data principles to be open for novel and unforeseen applications.