Dimitrios Koukopoulos

Handbook of research on technologies and cultural heritage : applications and environments

Lately, genealogy has become a hobby not only in the United States, UK or France but also in many other countries where it is now widespread. The main sources of information for genealogists are different kinds of genealogical documents (census, church vital records, wills, …). In fact, and specifically in Spain, several projects to digitalize heritage and genealogical documentation have developed recently, in order to improve its access and to preserve its conservation state. Such digital information is useful, but it would be even more useful to have its transcription in a searchable support like databases or web repositories. This chapter analyses the opportunities and characteristics of such transcription projects and describes a transcription user interface tool. This proposal allows for easy, intuitive and fast design of a user interface to transcript genealogical documentation, in agreement with the contents of each different kind of genealogical documents. Given an XML Schema (XSD) describing a genealogical document structure and contents, this tool allows the user to adapt and personalize a user interface to transcribe the document contents, while obtaining an XML file to be stored in some database management system or to be shared among genealogists. At any moment during the transcription process, user interface may be adapted to the user requirements and to the document characteristics, so, this adaption is dynamic, intuitive and user friendly.

Security in Collaborative Multimedia Web-based Art Projects

We propose a web-based system for organizing the creation and the interaction in multimedia web-based environments that permit the collaboration among artists, audience, curators and publishers. This system uses a threelevel approach for handling security issues in multimedia projects. Especially, it applies authorization, digital certification and watermarking mechanisms on multimedia content. Authorization mechanism controls users operations in multimedia files based on a set of actions imposed on reallife scenarios. Digital certification mechanism ensures the secure content transfers among users and multimedia content server through Web. Digital watermarking mechanism handles copyright-protection and authentication issues that appear in multimedia systems applying a semantically secure watermark. The strength of our system considers multimedia content not as an atomic digital entity, but as a part of a project with a specific workflow that applies watermarking techniques in all its parts.

The impact of dynamic link slowdowns on network stability

A very natural question that arises in the context of stability properties of packet-switched networks is how the dynamic changing of the network link slowdowns precisely affects these properties. In this work, we embark on a systematic study of this question adopting the adversarial, quasi-static slowdown queueing theory model, where an adversary controls the rates of packet injections, determines packet paths and manipulates link slowdowns. Within this model, we show that a network that uses the LIS (Longest-in-System) protocol for contention-resolution can be unstable for arbitrarily low injection rates. Moreover, we present involved combinatorial constructions of executions that improve the state-of-the-art instability bound induced by certain known forbidden subgraphs on networks running a certain greedy protocol. These bounds are lower than their known counterparts for the classical adversarial queueing theory model and other dynamic adversarial models.

The impact of dynamic adversarial attacks on the stability of heterogeneous multimedia networks

Modern large-scale multimedia networks, such as the Internet, are characterised by heterogeneity due to the versatile nature of the communication subsystems they consist of. We focus on heterogeneous networks where individual greedy, contention-resolution protocols are simultaneously running (composed) over different network queues. A question that arises in such settings of multimedia systems concerns the possibility of developing design criteria in order to evaluate performance degradation under dynamic adversarial attacks. A network is stable if the number of packets in its queues remains bounded at all times for any greedy protocol against any adversary of injection rate less than 1. We study stability properties under various compositions of protocols and dynamic adversarial attacks trying to characterise those properties in terms of network topologies for simple-path trajectories. We feel that this study could help on the design and maintenance of trustworthy heterogeneous networks.

Heterogenous networks can be unstable at arbitrarily low injection rates

A distinguishing feature of todays large-scale platforms for distributed computation and communication, such as the Internet, is their heterogeneity, predominantly manifested by the fact that a wide variety of communication protocols are simultaneously running over different distributed hosts. A fundamental question that naturally poses itself for such common settings of heterogeneous distributed systems concerns their ability to preserve or restore an acceptable level of performance during link failures. In this work, we address this question for the specific case of stability properties of greedy, contention-resolution protocols operating over a packet-switched communication network that suffers from link slowdowns. We focus on the Adversarial Queueing Theory framework, where an adversary controls the rates of packet injections and determines packet paths. In addition, the power of the adversary is enhanced to include the manipulation of link slowdowns. Within this framework, we show that the composition of LIS (Longest-in-System) with any of SIS (Shortest-in-System), NTS (Nearest-to-Source) and FTG (Furthest-to-Go) protocols is unstable at rates ρ > 0 when the network size and the link slowdown take large values. These results represent the current record for instability bounds on injection rate for compositions of greedy protocols over dynamic adversarial models, and also suggest that the potential for instability incurred by the composition of two greedy protocols may be worse than that of some single protocol.

The Impact of Dynamic Adversarial Attacks on the Stability of Heterogeneous Multimedia Networks

Modern large-scale multimedia networks, such as the Internet, are characterised by heterogeneity due to the versatile nature of the communication subsystems they consist of. We focus on heterogeneous networks where individual greedy, contention-resolution protocols are simultaneously running (composed) over different network queues. A question that arises in such settings of multimedia systems concerns the possibility of developing design criteria in order to evaluate performance degradation under dynamic adversarial attacks. A network is stable if the number of packets in its queues remains bounded at all times for any greedy protocol against any adversary of injection rate less than 1. We study stability properties under various compositions of protocols and dynamic adversarial attacks trying to characterise those properties in terms of network topologies for simple-path trajectories. We feel that this study could help on the design and maintenance of trustworthy heterogeneous networks.

An experimental study of stability in heterogeneous networks

A distinguishing feature of todays large-scale communication networks, such as the Internet, is their heterogeneity, predominantly manifested by the fact that a wide variety of communication protocols are simultaneously running over different network hosts. A fundamental question that naturally poses itself for such common settings of heterogeneous networks concerns their ability to preserve the number of packets in the system upper bounded at all times. This property is well-known as stability. We focus on the Adversarial Queueing Theory framework, where an adversary controls the rates of packet injections and determines packet paths. In this work, we present specific network constructions with different protocol compositions and we show experimentally their stability behavior under an adversarilly strategy. In particular, we study compositions of universally stable protocols with unstable protocols like FIFO. Interestingly, some of our results indicate that such a composition leads to a worst stability behavior than having a single unstable protocol for contention-resolution. This suggests that the potential for instability incurred by the composition of one universally stable protocol with one unstable protocol may be worse than that of some single protocol.

The Impact of FIFO Compositions with Other Protocols on the Stability of Multimedia Networks Facing Dynamic Adversarial Attacks

Multimedia packet-switched communication networks, such as the Internet, are heterogeneous in their nature due to the usage of different protocols for resolving packet conflicts on network queues and the existence of multiple types of network links. The efficiency of multimedia communication depends on the variety of contention-resolution protocols that are simultaneously running (composed) over different hosts and the capacities of links. We are mainly interested in FIFO compositions with other protocols because FIFO is widely used in packet-switched networks for best effort services due to its simplicity. A very natural question that arises in such common settings of multimedia networks concerns the degradation of network stability under adversarial attacks that change dynamically network link capacities. A packet-switched network is stable if the number of packets in the network remains bounded at all times against any adversary. We adopt an enhanced adversarial framework, where an adversary controls packet injection rates, packet paths and network link capacities. Within this framework, we study the impact of specific compositions of FIFO with other protocols on the network stability. Interestingly, our results suggest that such protocol compositions may lead a network to worse instability when it faces adversarial attacks that dynamically change link capacities than adversarial attacks with unit capacities or when a single content-resolution protocol is used. We feel that this study could help on the design of trustworthy multimedia networks.

Instability behaviour of heterogeneous multimedia networks under dynamic adversarial attacks

Abstract Multimedia communication networks, such as the Internet, are heterogeneous in their nature because they require different methods for content transmission. The efficiency of multimedia content transmission depends on the variety of communication protocols that are simultaneously running (composed) over different network hosts in order to resolve packet conflicts. A very natural question that arises in such common settings of multimedia networks concerns the degradation (or not) of network stability under adversarial attacks that change dynamically network link capacities/slowdowns. A packet-switched network is stable if the number of packets in the network remains bounded at all times against any adversary. In this work, we embark on a systematic study of this question adopting an enhanced adversarial framework, where an adversary controls the rates of packet injections, determines packet paths and manipulates link slowdowns or capacities. Such adversarial attacks can be considered as a type of denial of service attack. Within this framework, we study network stability under specific compositions of contention–resolution protocols when packets are injected with simple paths (paths can contain repeated edges, but not repeated nodes) trying to characterise this property in terms of network topologies. The examined network topologies have been proved forbidden for stability when network link capacities/slowdowns are fixed and packet paths are simple. Furthermore, in order to evaluate how unstable can a network be for the same protocol compositions under dynamic adversarial attacks, we present an involved adversarial construction that leads a specific network to instability for arbitrarily low injection rates. Interestingly, our results suggest that dynamic adversarial attacks changing link slowdowns may be worse than dynamic adversarial attacks changing link capacities or attacks with fixed slowdowns/capacities for specific protocol compositions.

Optimal algorithms for detecting network stability

A packet-switched network is universally stable if, for any greedy protocol and any adversary of injection rate less than 1, the number of packets in the network remains bounded at all times. A natural question that arises is whether there is a fast way to detect if a network is universally stable based on the networks structure. In this work, we study this question in the context of Adversarial Queueing Theory which assumes that an adversary controls the locations and rates of packet injections and determines packet paths. Within this framework, we present optimal algorithms for detecting the universal stability (packet paths do not contain repeated edges but may contain repeated vertices) and the simple-path universal stability (paths contain neither repeated vertices nor repeated edges) of a network. Additionally, we describe an algorithm which decides in constant time whether the addition of a link in a universally stable network leads it to instability; such an algorithm could be useful in detecting intrusion attacks.