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available at www.sciencedirect.com

journal homepage: www.elsevier.com/locate/cosrev

Survey

Introduction to the special issue onfoundations of adaptive networked societies of tiny artefacts

Ioannis Chatzigiannakis∗, Paul Spirakis

Research Academic Computer Technology Institute (RACTI), Patras, Greece

A R T I C L E I N F O

Article history:

Received 9 November 2010

Accepted 9 November 2010

Keywords:

Wireless sensor networks

Mobile networks

Distributed computing

Security

Computation models

Self-stabilization

Game theory

Streaming algorithms

Data aggregation

Algorithm engineering

Experimentation

Ubiquitous applications

A B S T R A C T

This special issue of Computer Science Review features seven papers on foundations of

adaptive networked societies of tiny artefacts. The introduction describes the motivation

for the special issue and briefly overviews the contributions.c⃝ 2010 Elsevier Inc. All rights reserved.

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In the last decade we have witnessed tremendousprogress towards the interconnection of the digital andphysical domains, as is also evidenced by the outstandingactivity in the wireless sensor networking research area andthe continuous integration of sensing devices in multipleapplication domains. Very recently we started looking athow to expand this ecosystem of embedded devices byfully integrating them into the web. The coexistence andcooperation of embedded systems with our social life isunveiling a brand new era of exciting possibilities.

Such systems are large networks of technical and techno-social nature. They comprise myriad units/nodes with

∗ Corresponding author.E-mail addresses: ichatz@cti.gr (I. Chatzigiannakis), spirakis@cti.

1574-0137/$ - see front matter c⃝ 2010 Elsevier Inc. All rights reservedoi:10.1016/j.cosrev.2010.11.003

r (P. Spirakis).

individual properties, objectives and actions. Each such

artefact is unimpressive: small, with limited sensing, signal

processing, and communication capabilities, and usually of

limited energy. They are organized in large societies of

networked tiny artefacts to accomplish tasks that are difficult

or beyond the capabilities of today’s conventional centralized

systems. Such systems are open, in that nodes may enter

or leave the collective at any time. Decision-making is

distributed and possibly highly dispersed, and interaction

between the units may lead to the emergence of unexpected

phenomena.

.

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These systems or societies have particular ways to achievean appropriate level of organization and integration; thisorganization is achieved seamlessly and with appropriatelevels of flexibility, in order to be able to accomplish the globalgoals and objectives. And they do this in a sensitive andproactive way to meet the current or anticipated needs oftheir “users”. For this reason, they adapt to the changes intheir environment and change their internal organization bycommunicating, cooperating, and forming goal-driven sub-organizations.

Our envisaged systems have an identified purpose (whichdepends on the application). Adaptation serves this purpose.This means that sudden variations of external servicerequests or environmental physical conditions or of themotion of the network nodes does not stop the system fromserving its goal. Instead the system continues to operate in aset of desired states with maintained, or gracefully degradedor even improved quality of service. Clearly, technologyexpects such systems to be dependable and adaptive: to theuser needs, sudden changes of the environment, and specificapplications characteristics.

This special issue surveys the work conducted inthe context of the EU-funded research project FRONTS.The project focuses on the algorithmic foundations ofadaptive networked societies of small or tiny heterogeneousartefacts. The three-year duration allowed us to develop anunderstanding of such societies and propose formal modelsthat capture the clue characteristics. Our models captureasynchronous dynamic local interactions, the use of localmemories of devices, as well as continuous interactions withthe environment. They enable us to predict the behavior,usefulness, effectiveness, efficiency and optimality of suchsystems in any kind of application.

The first article surveys some very recent ComputationalModels for networks of tiny artefacts. The models assumethat the artefacts move passively, that is, they are mobilebut unable to control their own movement. Specifically, thepopulation protocol model and enhancements are examined.Such models abstract the technical characteristics of low-power wireless “links” via the notion of a “rendezvous” ofnodes: an atomic operation where two artefacts can directlyexchange information for a small time period. Moreover,the sensor field model is presented, that captures thecontinuous input streams of sensed data that occur atseveral, distributed points of observation. The computationcapabilities of the various models are examined in relation tothe capabilities of the available hardware. The article presentssimulation results for sensor fields and population protocolsand analyzes the ability of their variants to decide graphproperties.

The second article surveys Streaming Techniques and DataAggregation in networks of tiny artefacts. The size of datacollected by sensing devices in streams typically far exceedsthe storage and computational capabilities of the tiny devicesthat have to collect and process them. The techniquesreviewed are fully decentralized and diffusive in nature:collecting all data at a few central nodes of the network isinfeasible in such networks. The techniques are classified onthe basis of the computational capabilities that they assumeand the applications that they effectively address.

The second goal of FRONTS is to produce schemesfor designing, developing and operating networks of tinyartefacts. Two sets of schemes have been proposed duringthe duration of the project: one set of schemes for theinternal continuous self-organization of the network, and anotherset of schemes for adapting and responding to external changesdynamically. Any distributed adaptive system must devotepart of its functionality to self-organizing internally. Thisself-organization activity is viewed as continuous and it isa very necessary overhead that the system pays, in orderto be ready to adapt (i.e., to react to changes in the externalenvironment). Thus, the first set of schemes focuses on themethods and network procedures that perform this internalpreparation. On the other hand, any adaptive system mustreact properly to external influences induced by changes ofthe environment. The system (the society of tiny artefacts)is assumed too large to be handled in a centralized manner.We have to design local strategies that are capable of handlingthe required global tasks. Such strategies should benefit fromthe internal reorganization methods of the network. The nextthree articles discuss such schemes for self-organization andadaptation of the network.

The third article surveys Innovative Approaches to Securityin networks of tiny artefacts. The article discusses theconceptual problems arising from security issues for smallartefacts. Two schemes for achieving the security of smallartefacts are reviewed. The first scheme deals with caseswhere the attackers have limited (but still much largerthan the defender) computation capabilities. The secondscheme captures cases where the tiny artefacts cannotconduct any task of interest unless a set of supportingelements are pervasively positioned in the environment fromwhich the artefacts receive services and information. In thissetting, trust plays a central role and lack of trust makesthe problem interesting and challenging; if the artefactscompletely trust the environment (and they should not) thenthe problem becomes trivial as the environment can conductevery security operation on behalf of the artefacts. Thescheme enables the outsourcing of some of the computationprescribed by the security protocol to an untrusted intelligentenvironment without having to sacrifice security.

The fourth article surveys Relay Placement in networksof tiny artefacts. Techniques are reviewed for pervasivelyplacing supporting elements within the environment of thetiny artefacts. Such supporting elements may offer limitedcomputation capabilities (but still much larger than those ofthe tiny artefacts). In certain cases these supporting elementsmay also be actively mobile. These elements may alsooffer low-cost communication services for the artefacts. Allschemes reviewed provide provable performance guaranteessuch as upper bounds on the required runtime, maximumtraveled distances of the relays and approximation factors forthe solution.

The fifth article reviews Robust and Scalable Middlewarefor networks of tiny artefacts. It captures cases where theartefacts are executing heterogeneous software and thenetwork may employ elements of byzantine nature. Certainschemes are reviewed that establish a robust, distributedand self-stabilizing supporting authority that can secure theoperation of the network.

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During the second year and third year of FRONTSwe designed and implemented several large “unifying”experiments (and nine smaller scope experiments) in whichwe tested our schemes and measured their performance.FRONTS produced a sizable amount of very innovativesoftware (all available from the project’s code repository).Some of this software gained golden awards internationally,in the application area of pervasive dynamic gaming forrecreation. The majority of our experiments were conductedin testbeds comprised of real heterogeneous hardwaredevices. The next two articles discuss the tools andmethodologies available for conducting experiments and usethe software to develop applications that use networks of tinyartefacts.

The sixth article surveys tools and methodologies forDistributed Algorithm Engineering for networks of tiny artefacts.The article reviews the state of the art for experimentallydriven research on networks of tiny artefacts. The maintopics are existing and planned practical testbeds, softwaresimulations, and hybrid approaches. It also reviews twostudies of distributed algorithm engineering undertakenwithin the project FRONTS.

The seventh article surveys the Challenges, Scenarios andCase Studies for Urban Pervasive Applications that are basedon networks of tiny artefacts. This article reviews variousaspects of the application of pervasive technologies in anurban setting. In the last decade we have seen the emergenceof a multitude of closely related pervasive technologies thathave only recently started to materialize on a grand scale,such as wireless sensor networks, RFID and NFC. The arisingresearch challenges are discussed and associated with suchconverging fields. Moreover, the state of the art for relatedapplication scenarios is reviewed. Finally, a more analyticsurvey is presented for three discrete systems that belong tothis category of applications and give insight into the currentstate of the art for work in this field.

Acknowledgement

This work was supported by the ICT Programme of theEuropean Union (http://fronts.cti.gr) under contract numberICT-2008-215270 (FRONTS).