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Integrating data mining techniques into database systems has gained popularity and its significance is well recognized. However, the performance of SQL based data mining is known to fall behind specialized implementations. Reasons for this are among others the prohibitive nature of the cost associated with extracting knowledge as well as the lack of suitable declarative query language support. Recent studies have found that for association rule mining and sequential pattern mining with carefully tuned SQL formulations it is possible to achieve performance comparable to systems that cache the data in files outside the DBMS. However, most of the previous pattern mining methods follow the method of Apriori, which still encounters problems when a sequential database is large and/or when sequential patterns to be mined are numerous and long. In this paper, we present a novel SQL based approach that we recently proposed, called Prospad (PROjection Sequential PAttern Discovery). Prospad fundamentally differs from an Apriori-like candidate set generation-and-test approach. This approach is a pattern growth-based approach without candidate generation. It grows longer patterns from shorter ones by successively projecting the sequential table into subsequential tables. Since a projected table for a sequential pattern i contains all and only necessary information for mining the sequential patterns that can grow from i, the size of the projected table usually reduces quickly as mining proceeds to longer patterns. Moreover, a depth first approach is used to facilitate the projecting process in order to avoid creating and dropping costs of temporary tables. [ABSTRACT FROM AUTHOR]

Ontologies are an important technology for the Semantic Web. In different areas ontologies have already been developed and many of these ontologies contain overlapping information. Often we would therefore want to be able to use multiple ontologies. To obtain good results, we need to find the relationships between terms in the different ontologies, i.e. we need to align them. Currently, there exist a number of systems that support users in aligning ontologies, but not many comparative evaluations have been performed and there exists little support to perform such evaluations. However, the study of the properties, the evaluation and comparison of the alignment strategies and their combinations, would give us valuable insight in how the strategies could be used in the best way. In this paper we propose the KitAMO framework for comparative evaluation of ontology alignment strategies and their combinations and present our current implementation. We evaluate the implementation with respect to performance. We also illustrate how the system can be used to evaluate and compare alignment strategies and their combinations in terms of performance and quality of the proposed alignments. Further, we show how the results can be analyzed to obtain deeper insights into the properties of the strategies. [ABSTRACT FROM AUTHOR]

The Semantic Web envisions a world-wide distributed architecture where computational resources will easily inter-operate to coordinate complex tasks such as query answering. Semantic marking up of web resources using ontologies is expected to provide the necessary glue for making this vision work. Using ontology languages, (communities of) users will build their own ontologies in order to describe their own data. Adding semantic mappings between those ontologies, in order to semantically relate the data to share, gives rise to the Semantic Web: data on the web that are annotated by ontologies networked together by mappings. In this vision, the Semantic Web is a huge semantic peer data management system. In this paper, we describe the SomeRDFS peer data management systems that promote a "simple is beautiful" vision of the Semantic Web based on data annotated by RDFS ontologies. [ABSTRACT FROM AUTHOR]

A data warehouse (DW) is a database that integrates data from external data sources (EDSs) for the purpose of advanced analysis. EDSs are production systems that often change not only their contents but also their structures. The evolution of EDSs has to be reflected in a DW that integrates the sources. Traditional DW systems offer a limited support for the evolution of their structures. Our solution to this problem is based on a multiversion data warehouse (MVDW). Such a DW is composed of the sequence of persistent versions, each of which describes a schema and data within a given time period. The management of the MVDW requires a metadata model that is much more complex than in traditional data warehouses. In our approach and prototype MVDW system, the metadata model contains data structures that support: (1) monitoring EDSs with respect to content and structural changes, (2) automatic generation of processes monitoring EDSs, (3) applying discovered EDS changes to a selected DW version, (4) describing the structure of every DW version, (5) querying multiple DW versions at the same time and presenting the results coming from multiple versions. [ABSTRACT FROM AUTHOR]

The goal of Model Management is the development of new technologies and mechanisms to support the integration, evolution and matching of data models at the conceptual and logical design level. Such tasks are to be performed by means of a set of model management operators which work on models and their elements, without being restricted to a particular metamodel (e.g. the relational or UML metamodel). We propose that generic model management should employ a generic metamodel (GMM) which serves as an abstraction of particular metamodels and preserves as much of the original features of modeling constructs as possible. A naive generalization of the elements of concrete metamodels in generic metaclasses would lose some of the specific features of the metamodels, or yield a prohibitive number of metaclasses in the GMM. To avoid these problems, we propose the Generic Role based MetamodelGeRoMe in which each model element is decorated with a set of role objects that represent specific properties of the model element. Roles may be added to or removed from elements at any time, which enables a very flexible and dynamic yet accurate definition of models. Roles expose to operators different views on the same model element. Thus, operators concentrate on features which affect their functionality but may remain agnostic about other features. Consequently, these operators can use polymorphism and have to be implemented only once using GeRoMe, and not for each specific metamodel. We verified our results by implementing GeRoMe and a selection of model management operators using our metadata system ConceptBase. [ABSTRACT FROM AUTHOR]

Classifications have been used for centuries with the goal of cataloguing and searching large sets of objects. In the early days it was mainly books; lately it has also become Web pages, pictures and any kind of digital resources. Classifications describe their contents using natural language labels, an approach which has proved very effective in manual classification. However natural language labels show their limitations when one tries to automate the process, as they make it very hard to reason about classifications and their contents. In this paper we introduce the novel notion of Formal Classification, as a graph structure where labels are written in a propositional concept language. Formal Classifications turn out to be some form of lightweight ontologies. This, in turn, allows us to reason about them, to associate to each node a normal form formula which univocally describes its contents, and to reduce document classification and query answering to reasoning about subsumption. [ABSTRACT FROM AUTHOR]

A viable ontology engineering methodology requires supporting domain experts in gradually building and managing increasingly complex versions of ontological elements and their converging and diverging interrelationships. Contexts are necessary to formalise and reason about such a dynamic wealth of knowledge. However, context dependencies introduce many complexities. In this article, we introduce a formal framework for supporting context dependency management processes, based on the DOGMA framework and methodology for scalable ontology engineering. Key notions are a set of context dependency operators, which can be combined to manage complex context dependencies like articulation, application, specialisation, and revision dependencies. In turn, these dependencies can be used in context-driven ontology engineering processes tailored to the specific requirements of collaborative communities. This is illustrated by a real-world case of interorganisational competency ontology engineering. [ABSTRACT FROM AUTHOR]

This paper describes a theoretical framework for inducing knowledge from incomplete data sets. The general framework can be used with any formalism based on a lattice structure. It is illustrated within two formalisms: the attribute-value formalism and Sowa's conceptual graphs. The induction engine is based on a non-supervised algorithm called default clustering which uses the concept of stereotype and the new notion of default subsumption, inspired by the default logic theory. A validation using artificial data sets and an application concerning the extraction of stereotypes from newspaper articles are given at the end of the paper. [ABSTRACT FROM AUTHOR]

In this paper we propose the use of non-persistent CSMA as an anti-collision procedure for RFID active tags. Current proposals for both passive and active tags are based on the framed slotted ALOHA protocol, which does not scale well requiring additional procedures for frame length adaptation. However, active RFID devices already include carrier sense capabilities with no additional cost and, thus, CSMA may be employed seamlessly. Nevertheless, selecting the contention micro-slots of CSMA in the classical way (i.e., with a uniform distribution and an exponential back-off algorithm) does not result in an efficient identification process, as we will demonstrate. Fortunately, better choices can be found. Recently, an optimal distribution for the selection of micro-slots for event-driven sensor networks has been computed, as well as a practical implementation: the Sift distribution. In this work we propose the application of the quasi-optimal Sift distribution along with CSMA for active tag identification. By means of an analytical study, we evaluate the average time needed for identification with this mechanism and compare it with the current ISO 18000-7 and EPC "Gen 2" standard. The results reveal that the Sift-based non-persistent CSMA outperforms both of them. Moreover, it also scales much better, without the need for further adaptation mechanisms. [ABSTRACT FROM AUTHOR]

This paper presents a CDMA closed-loop power control (CLPC) using channel prediction in time-varying mobile fading channels. The proposed CLPC that relies on least square (LS) or least mean square (LMS) based autoregressive (AR) low-rate prediction provides a particularly robust performance for large loop delays, especially in the presence of channel estimation errors. As the mobility increases the proposed CLPC reduces mean-square error (MSE) further than conventional CLPCs. The Monte-Carlo simulation results demonstrate the superiority of the proposed CLPC over conventional nonpredictive and predictive CLPCs. [ABSTRACT FROM AUTHOR]

Cognitive radio (CR) has been proposed as an effective technology for flexible use of the radio spectrum. The interference among primary users and CR users, however, becomes a critical problem when they are operating nearby using adjacent frequency channels with different transmission powers. In this paper, a CR-based bandwidth sharing architecture is proposed, which can effectively suppress adjacent channel interference (ACI) between them. This new approach is characterized by the adaptive frequency spreading, and the adaptive time spreading with power control for the subcarriers near the borders of the CR user's spectrum. The frequency spreading scheme provides with extra power gain against ACI, whereas the time spreading with power control guarantees the minimal interference to primary users from CR users. By computer simulation, it has been proved that the proposed system outperforms the conventional OFDM systems in both throughput and BER performance. [ABSTRACT FROM AUTHOR]

Under dynamic time division duplexing (D-TDD) architecture in OFDM cellular systems, the inter-BS and inter-MS interference is inevitable during the cross time slot (CTS) period, and this interference seriously degrades the wireless access system performance. To mitigate such interference, we propose a region and time partitioning D-TDD architecture for OFDM systems. Each time slot in the CTS period is split into several minislots, and then each cell is divided into as many regions as the number of minislots per time slot. We then assign each minislot only to the users in its corresponding region. On top of such architecture, which inherently separates interfering entities farther from each other, we design a robust time slot allocation scheme considering the channel status of each mobile station. By computer simulation, it has been verified that the proposed scheme outperforms conventional time slot allocation methods in both the outage probability and the bandwidth efficiency. [ABSTRACT FROM AUTHOR]

This paper deals with a simple way of reducing the multiple access interference (MAI) introduced by symbol timing misalignment in an OFDMA uplink system. To alleviate the MAI, we provide a new OFDMA transmitter equipping with a simple symbol repetition coupled with a cyclic time shift. It is found that this scheme can provide the MAI-robust reception without decreasing the bandwidth efficiency when the system is fully loaded. [ABSTRACT FROM AUTHOR]

The IEEE 802.11 standard defines a medium access control protocol for wireless local area networks (WLANs). In typical WLANs, access points (APs) are connected with one another in a wired manner. As a way to loosen this restriction wireless mesh networks (WMNs), which are rather independent of a backbone infrastructure, is emerging. Due to their inherent characteristics unlike ad hoc networks, it is unreasonable that the ad hoc network routing protocols are directly applied for the WMNs without any modification. The tree-based routing protocol (TRP) defined in the IEEE 802.11s is one of the routing protocols used in WMNs. The TRP, however, forwards data on the only one active path. In this paper, we propose a flexible tree-based routing protocol with a mesh relaying node (TRP-MRN) in WMNs. The TRP-MRN provides a concurrent multi-path establishment algorithm. We analyze the end-to-end delay of the TRP and the TRP-MRN and show that the TRP-MRN can effectively reduce the end-to-end delay and provide alternative routes via simulations. [ABSTRACT FROM AUTHOR]

Vehicular ad-hoc networks (VANETs) offer a large number of new potential applications without relying on significant infrastructure. Many of these applications benefit from multi-hop relaying of information, thus requiring a routing protocol. Characteristics unique to VANETs (such as high mobility and the need for geographical addressing) make many conven tional ad hoc routing protocols unsuitable. Also, some envisioned applica tions have end-to-end QoS requirements. In this paper we propose a new multicast routing protocol specifically designed for VANETs. Its purpose is to provide a routing service for a future reliable transport protocol. We eval uate its performance using realistic network and traffic models. It is shown that it is possible to implement a reliable multicast routing protocol for VANETs. [ABSTRACT FROM AUTHOR]

Mobile Ad Hoc networks (MANETs) are susceptible to having their effective operation compromised by a variety of security attacks. Nodes may misbehave either because they are malicious and deliberately wish to disrupt the network, or because they are selfish and wish to conserve their own limited resources such as power, or for other reasons. In this paper, we present a mechanism that enables the detection of nodes that exhibit packet forwarding misbehavior. We present evaluation results that demonstrate the operation of our algorithm in mobile ad hoc environments and show that it effectively detects nodes that drop a significant fraction of packets. [ABSTRACT FROM AUTHOR]

In this paper we present an extension to the OLSR unicast routing protocol to support multicast routing in mobile ad hoc networks. The proposed protocol is based on Multicast Overlay Spanning Trees (MOST). The main benefits of this approach are twofold. Firstly, it implies that only nodes interested in taking part in the multicast communication need to participate in the protocol operation, which is transparent to other OLSR nodes. In addition, the MOST approach scaling properties achieve the theoretical performance bounds concerning the capacity of multicast communication in massive ad hoc networks. We perform simulations of the MOST protocol under the ns-2 simulator to compare with the theoretical results, and we present a fully working implementation for real network environments. [ABSTRACT FROM AUTHOR]

With the rapid improvement of wireless networking technologies, current mobile devices can be potentially equipped with multiple interfaces to access different kinds of wireless networks. Thus, there have been many efforts to provide a seamless roaming between heterogeneous networks. However, most previous studies do not address how to select the best possible interface in terms of energy consumption. Therefore, in this paper, we propose to take advantage of accurate location positioning via WWAN interface, so that Mobile Nodes (MNs) obtain the information of hotspot range and completely turn off WLAN interface during idle state, leading to save energy consumption. Simulation results show that our mechanism outperforms existing approaches in terms of energy consumption and signaling overhead. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a cross-layer diversity framework for multi-air interface wireless communication devices. As an initial step, we focus on devices, of the cellular phones type, that have both long-range relatively low-rate communication air-interface (e.g., GSM) and short-range high-rate communication air-interface (e.g., IEEE802.11). The devices can cooperate through the energy-efficient high-rate interface to improve the performance of the long-range interface. Within this framework we propose a distributed signal-combining technique that accounts for the limited bandwidth of the short-range communication: Threshold Maximum Ratio Combining. We analytically derive the probability distribution function of the signal to noise ratio (SNR) of the combined signals as a function of the number of involved devices and show that significant improvement of the SNR is achievable which translates into a reduction of the overall system outage probability. [ABSTRACT FROM AUTHOR]

In this paper we present the distributed event localization and tracking algorithm DELTA that solely depends on light measurements. Based on this information and the positions of the sensors, DELTA is able to track a moving person equipped with a flashlight by dynamically building groups and electing well located nodes as group leaders. Moreover, DELTA supports object localization. The gathered data is sent to a monitoring entity in a fixed network which can apply pattern recognition techniques to determine the legitimacy of the moving person. DELTA enables object tracking with minimal constraints on both sensor hardware and the moving object. We show the feasibility of the algorithm running on the limited hardware of an existing sensor platform. [ABSTRACT FROM AUTHOR]

Providing security services for wireless sensor networks plays a vital role in secure network operation especially when sensor networks are deployed in hostile areas. In order to pave the way for these mechanisms, cryptographic keys must be agreed on by communicating nodes. Unfortunately, due to resource constraints, the key agreement problem in wireless sensor networks becomes quite intricate. To deal with this problem, many public-key unrelated proposals have been proposed so far. One prominent branch of these proposals is based on random key pre-distribution. Inspired by this trend, in this paper, we propose a new random key pre-distribution scheme that is comparable to Du et al.'s scheme [2] in terms of network resiliency and memory usage. On the other hand, our later analysis shows that our scheme outperforms Du et al.'s scheme in terms of computational and communication overhead. [ABSTRACT FROM AUTHOR]

We propose a layered quality adaptation scheme for video streams to smooth the short-term oscillations induced by Additive Increase Multiplicative Decrease (AIMD) mechanisms, and eventually refine the perceptual video quality. The layered scheme utilizes receiver buffering, adapting the video quality along with long-term variations in the available bandwidth. The allocation of a new layer is based on explicit criteria that consider the available bandwidth, as well as the amount of buffering at the receiver. Consequently, the adaptation mechanism prevents wasteful layer changes that have an adverse effect on user-perceived quality. In the sequel, we concentrate on the interactions of the layered approach with Scalable Streaming Video Protocol (SSVP). Exploiting performance measures related to the perceived quality of rate-adaptive video streams, we quantify the combination of SSVP rate control and receiver-buffered layered adaptation. [ABSTRACT FROM AUTHOR]

First order metrics (throughput, average delay) of the IEEE 802.11 DCF MAC protocol have been extensively analyzed. The service process of the same protocol has not received the same attention, although it is known that it might be bursty. We develop a simple and accurate Markov model that allows a complete characterization of the service process of an 802.11 BSS. A major result of simulations is that correlation between consecutive service times is negligible, hence the service process can be safely described as a renewal process. The analytic model highlights that service burstiness lies essentially in the doubling of the contention window after a collision up to very large values. The trade-off between average throughput and service burstiness is obtained from the model. [ABSTRACT FROM AUTHOR]

This paper presents analysis of the performance on the IEEE 802.11b in the presence of multiple IEEE 802.15.4 interferences. To analyze the performance, packet error rate (PER) and throughput are used as performance metrics. The PER is computed by the bit error rate (BER), the collision time and the number of IEEE 802.15.4 interferers in the presence of in-band of the IEEE 802.11b. The throughput of the IEEE 802.11b under multiple IEEE 802.15.4 interferences is obtained from the total IEEE 802.11b packet length received during a specified time. Analytic results of the performance of IEEE 802.11b under multiple IEEE 802.15.4 interferences are verified by simulation results. These results can support coexistence criteria for the IEEE 802.11b and the IEEE 802.15.4. [ABSTRACT FROM AUTHOR]

It is well known that the presence of nodes using a low data transmit rate has a disproportionate impact on the performance of an IEEE 802.11 WLAN. ORP is an opportunistic relay protocol that allows nodes to increase their effective transmit rate by replacing a low data rate transmission with a two-hop sequence of shorter range, higher data rate transmissions, using an intermediate node as a relay. ORP differs from existing protocols in discovering relays experimentally, by optimistically making frames available for relaying. Relays identify themselves as suitable relays by forwarding these frames. This approach has several advantages compared with previously proposed relay protocols: Most importantly, ORP does not rely on observations of received signal strength to infer the availability of relay nodes and transmit rates. We present analytic and simulation results showing that ORP improves the throughput by up to 40% in a saturated IEEE 802.11b network. [ABSTRACT FROM AUTHOR]

Since Integrated Services architecture is not scalable, it seems the only solutions for Quality of Service (QoS) architecture in the Internet are Differentiated Services (DiffServ) or its variations. It is generally understood that networks with DiffServ architectures can guarantee the end-to-end delay for packets of the highest priority class, only in lightly utilized networks. We show that, in networks without loops, the delay bounds for highest priority packets exist regardless of the level of network utilization with DiffServ architecture. These bounds are quadratically proportional to the maximum hop counts in heavily utilized networks; and are linearly proportional to the maximum hop counts in lightly utilized networks. We argue that, based on the analysis of these delay bounds in realistic situations, DiffServ architecture is able to support real time applications even in large networks. Considering that loop-free networks, especially the Ethernet networks, are being adopted more than ever for access networks and for provider networks as well, this conclusion is quite encouraging. Throughout the paper we use Latency-Rate ($\mathcal{LR}$) server model, with which it has been proved that FIFO and Strict Priority schedulers are $\mathcal{LR}$ servers to each flows in certain conditions. [ABSTRACT FROM AUTHOR]

This paper describes network level simulation results for VoIP and Best Effort traffic running over HSDPA. The main focus involves an analysis of how the system is able to deal with user mobility, and in particular handover. Both a handover threshold level as well as a handover setup delay have been included in the simulation model, and a discard timer is used to remove outdated packets from the Node B queue. Link adaptation and H-ARQ (Hybrid-Automatic Repeat reQuest) functionalities are also included in the simulator. An infinite multi-cell environment has been modeled and the users are assumed to move at vehicular speeds. A performance analysis will show the end-to-end QoS. The handover threshold, delay and discard times are also varied in order to investigate their impact on the performance. [ABSTRACT FROM AUTHOR]

The explosive growth of VoIP traffic poses a potential challenge to the stability of the Internet that, up to now, has been guaranteed by the TCP congestion control. In this paper, we investigate how Skype behaves in the presence of time-varying available bandwidth in order to discover if some sort of congestion control mechanism is implemented at the application layer to match the network available bandwidth and cope with congestion. We have found that Skype flows are somewhat elastic, i.e. they employ some sort of congestion control when sharing the bandwidth with unresponsive flows, but are inelastic in the presence of classic TCP responsive flows, which provokes extreme unfair use of the available bandwidth in this case. Finally, we have found that when more Skype calls are established on the same link, they are not able to adapt their sending rate to correctly match the available bandwidth, which would confirm the risk of network congestion collapse. [ABSTRACT FROM AUTHOR]

This paper proposes a novel traffic engineering framework able to automatically provide near-optimal OSPF routing configurations for QoS constrained scenarios. Within this purpose, this work defines a mathematical model able to measure the QoS compliance in a class-based networking domain. Based on such model, the NP-hard optimization problem of OSPF weight setting is faced resorting to Evolutionary Algorithms. The presented results show that, independently of other QoS aware mechanisms that might be in place, the proposed framework is able to improve the QoS level of a given domain only taking into account the direct influence of the routing component of the network. The devised optimization tool is able to optimize OSPF weight configurations in scenarios either considering a single level of link weights or using multiple levels of weights (one for each class) in multi-topology routing scenarios. [ABSTRACT FROM AUTHOR]

The P-SHIM6 architecture provides ISP independence to IPv6 sites without compromising scalability. This architecture is based on a middle-box, the P-SHIM6, which manages the SHIM6 protocol exchange on behalf of the nodes of a site, which are configured with provider independent addresses. Incoming and outgoing packets are processed by the P-SHIM6 box, which can assign different locators to a given communication, either when it is started, or dynamically after the communication has been established. As a consequence, changes required for provider portability are minimized, and fine-grained Traffic Engineering can be enforced at the P-SHIM6 box, in addition to the fault tolerance support provided by SHIM6. [ABSTRACT FROM AUTHOR]

Differentiated Services (DiffServ) are seen as the technology to support Quality of Service (QoS) in IP networks in a scalable manner by allowing traffic aggregation within the engineered traffic classes. In DiffServ domains, admission control additionally needs to be employed in order to control the amount of traffic into the engineered traffic classes so as to prevent overloads that can lead to QoS violations. In this paper we present an admission control scheme for inter-domain real-time traffic originating from DiffServ stub domains; that is real-time traffic originating from end-users connected to a DiffServ stub domain towards destinations outside the geographical scope of that domain. By means of simulations we show that our scheme performs well and that it compares favorably against other schemes found in the literature. [ABSTRACT FROM AUTHOR]

In this study, we analyze security and quality of service (QoS) issues in cluster-based wireless sensor networks (WSN). Taking spatial resolution as the main QoS metric and limiting the security definition to data integrity and authentication, we present a control strategy to maintain desired QoS and security levels during the entire operation of a cluster-based sensor network. Besides, our proposed strategy considers some other WSN QoS attributes such as coverage, packet collision and system lifetime. It provides sufficient coverage by statistical means and minimizes packet loss due to collisions by employment of a slotted MAC (media access control) scheme. It also tries to maximize the operational lifetime of the sensor network by a power conserving scheme which make all sensors participate equally. In this study, we also determine the best tradeoff between security and spatial resolution. [ABSTRACT FROM AUTHOR]

It is sometimes believed that a "broadband access" network, providing ample transmission capacity to residential environments, is enough so as to allow a flawless delivery of advanced services. However, the provisioning of a combination of multiple services with guaranteed quality up to the end-user terminal requires a carefully designed architecture incorporating the appropriated Quality of Service (QoS) concepts throughout the data path. And this path includes the Residential Gateway (RGW) as the last hop towards the home network. This paper describes the different experiences performed with the RGW prototype developed within the framework of the European IST research project MUSE. Special emphasis will be made on the QoS capabilities of the RGW as well as on authentication and auto-configuration features. [ABSTRACT FROM AUTHOR]

Seamless handover over heterogeneous mobile environments is a major requirement to the success of the next generation of networks. However, seamless movement requires the control of the quality level and connectivity of communication sessions with no perceived service degradation to the users. This seamless characteristic is equally important for communication sessions encompassing only one or multiple receivers, being the latter called multi-user sessions. This paper presents a solution to allow seamless mobility for multi-user sessions over heterogeneous networks with mobile receivers and static senders. The proposed solution integrates end-to-end Quality of Service (QoS) mapping, QoS adaptation and connectivity control with seamless mobility support. The latter is achieved by using buffers in the mobile nodes and caches in the access-routers together with mobility prediction and context transfer schemes. Simulations present the efficiency of this proposal to setup ongoing sessions and its impact in reducing packet losses during movement. [ABSTRACT FROM AUTHOR]

This paper analyses security mechanisms in wireless networks, and designs for secure and efficient protocol for a handover reusing the key materials generated before the handover phase. In order to be sure that our handover protocol does not have any security flaws, we formally validated it using automatic protocol analyzer AVIPSA. [ABSTRACT FROM AUTHOR]

In mobile IPv6 network, the handoff latency for mobile node challenges service quality of real-time stream media applications. This paper proposes an improved handover scheme for stream media applications, which switch data-stream to foreign network link predictively by session-level handover between mobile and correspondent node. And to reduce the duration of dual-stream transmission in network, a time-compensation mechanism is used. The scheme works at session-level independently, and requires no modification to current standards and protocols. Simulation results show that the scheme effectively improves the handoff latency and packet-losses for stream media applications. [ABSTRACT FROM AUTHOR]

This paper studies the effect of path delay on SCTP performance. It focuses on the SCTP fast retransmit algorithm and demonstrates that the performance in the current retransmission strategy will degrade acutely when the secondary path delay is less than the primary path delay at a certain level. The performance degradation is due to the disordered SACKs and constant congestion window size during the fast retransmit phase. Some modifications aimed at these problems are proposed and evaluated. This paper also identifies that the cause of the performance degradation in SCTP is a result of the single path configuration oriented design of the current fast retransmit algorithm. Several fast retransmission strategies are evaluated for different path delay and bandwidth configurations. [ABSTRACT FROM AUTHOR]

We propose a combined transport - medium access control (MAC) layer scheme to provide relative service differentiation to Transmission Control Protocol (TCP) flows over a geostationary (GEO) bandwidth on demand (BoD) satellite networks. Our approach involves the joint configuration of TCP-Performance Enhancing Proxy (TCP-PEP) agents at the transport layer and the scheduling algorithm controlling the resource allocation at the MAC layer. The scheme is independent of the TCP variant used in the network. Extensive simulation results show that the two mechanisms exhibit complementary behavior in achieving the desired differentiation throughout the traffic load space: the TCP-PEP agents control differentiation at low system utilization, whereas the MAC scheduler becomes the dominant differentiation factor at high load. [ABSTRACT FROM AUTHOR]

Current standard defines two variants of TCP NewReno: the Slow-but-Steady and Impatient. While the behavior of various TCP implementations has been extensively studied over the last years, little attention has been paid to performance analysis of different variants of TCP NewReno. In this paper, we first develop an analytical model of the Impatient variant, which being combined with the earlier proposed model of the Slow-but-Steady variant gives a comprehensive analytical model of TCP NewReno throughput. We then make an analytical comparison of the Impatient and Slow-but-Steady throughputs in the presence of correlated losses. We show that, although neither of the two variants is optimal, the Impatient variant provides the same throughput as the Slow-but-Steady one in a wide range of network conditions and significantly outperforms it in case of large windows and multiple packet drops. This could be of special interest for networks with large bandwidth and long delay. [ABSTRACT FROM AUTHOR]

It is well known that one of the critical sources of TCP poor performance in multihop ad hoc networks lies in the TCP window mechanism that controls the amount of traffic sent into the network. In this paper, we propose a novel cross layer solution called "TCP Contention Control" that dynamically adjusts the amount of outstanding data in the network based on the level of contention experienced by packets as well as the throughput achieved by connections. Our simulation results show TCP Contention Control can drastically improve TCP performance over 802.11 multihop ad hoc networks. [ABSTRACT FROM AUTHOR]

This paper studies a gathering problem for a system of asynchronous autonomous mobile robots that can move freely in a two-dimensional plane. We consider robots equipped with inaccurate (incorrect) compasses which may point a different direction from other robots' compasses. A gathering problem is that the robots are required to eventually gather at a single point which is not given in advance from any initial configuration. In this paper, we propose several inaccurate compass models and give two algorithms which solve the gathering problem on these models. One algorithm is the first result dealing with the compasses whose indicated direction may change in every beginning of execution cycles of robots. It solves the problem when compasses point different at most π/8 from the (absolute) north. The other one solves the problem when the compasses never change its pointed direction and their difference is at most π/3 among robots. [ABSTRACT FROM AUTHOR]

This paper studies the problem of broadcasting in synchronous point-to-point networks, where one initiator owns a piece of information that has to be transmitted to all other vertices as fast as possible. The model of fractional dynamic faults with threshold is considered: in every step either a fixed number T, or a fraction α, of sent messages can be lost depending on which quantity is larger. As the main result we show that in complete graphs and hypercubes it is possible to inform all but a constant number of vertices, exhibiting only a logarithmic slowdown, i.e. in time O(Dlogn) where D is the diameter of the network and n is the number of vertices. Moreover, for complete graphs under some additional conditions (sense of direction, or α< 0.55) the remaining constant number of vertices can be informed in the same time, i.e. O(logn). [ABSTRACT FROM AUTHOR]

The problem we consider originates from the design of efficient on-board networks in satellites (also called Traveling Wave Tube Amplifiers). Signals incoming in the network through ports have to be routed through an on-board network to amplifiers. The network is made of expensive switches with four links and subject to two types of constraints. First, the amplifiers may fail during satellite lifetime and cannot be repaired. Secondly, as the satellite is rotating, all the ports are not well oriented and hence not available. Let us assume that we have p + λ ports (inputs) and p + k amplifiers (outputs), then a network is said to be valid if, for any choice of p inputs and p outputs, there exist p edge-disjoint paths linking all the chosen inputs to all the chosen outputs. Then, the objective is to design a valid network having the minimum number of switches denoted . In the special case where λ= 0, these networks were already studied as selectors. Here we present validity certificates from which derive lower bounds for ; we also provide constructions of optimal (or quasi optimal) networks for practical values of λ and k (1 ≤ λ ≤ k ≤ 8) and a general way to build networks for any k and any λ. [ABSTRACT FROM AUTHOR]

We study parallel knock-out schemes for graphs. These schemes proceed in rounds in each of which each surviving vertex simultaneously eliminates one of its surviving neighbours; a graph is reducible if such a scheme can eliminate every vertex in the graph. We show that, for a reducible graph G, the minimum number of required rounds is $O{({\sqrt{\alpha}})}$, where α is the independence number of G. This upper bound is tight and the result implies the square-root conjecture which was first posed in MFCS 2004. We also show that for reducible K1,p-free graphs at most p − 1 rounds are required. It is already known that the problem of whether a given graph is reducible is NP-complete. For claw-free graphs, however, we show that this problem can be solved in polynomial time. [ABSTRACT FROM AUTHOR]

Let G be a kG-edge connected graph and denote the diameter of G after deleting any of its c < kG edges. We prove that if G1, G2..., Gq are k1-edge connected, k2-edge connected,..., kq-edge connected graphs and 0 ≤ a1 < k1, 0 ≤ a2 < k2,..., 0 ≤ aq < kq and a = a1 + a2 + ... + aq + (q − 1), then the edge fault-diameter of G, the Cartesian product of G1, G2..., Gq, with a faulty edges is [ABSTRACT FROM AUTHOR]

We consider the problem of characterizing user equilibria and optimal solutions for selfish routing in a given network. We extend the known models by considering users oblivious to congestion. While in the typical selfish routing setting the users follow a strategy that minimizes their individual cost by taking into account the (dynamic) congestion due to the current routing pattern, an oblivious user ignores congestion altogether. Instead, he decides his routing on the basis of cheapest routes on a network without any flow whatsoever. These cheapest routes can be, for example, the shortest paths in the network without any flow. This model tries to capture the fact that routing tables for at least a fraction of the flow in large scale networks such as the Internet may be based on the physical distances or hops between routers alone. The phenomenon is similar to the case of traffic networks where a certain percentage of travelers base their route simply on the distances they observe on a map, without thinking (or knowing, or caring) about the delays experienced on this route due to their fellow travelers. In this work we study the price of anarchy of such networks, i.e., the ratio of the total latency experienced by the users in this setting over the optimal total latency if all users were centrally coordinated. [ABSTRACT FROM AUTHOR]

A set of input vectors S is conclusive if correct functionality for all input vectors is implied by correct functionality over vectors in S. We consider four functionalities of comparator networks: sorting, merging of two equal length sorted vectors, sorting of bitonic vectors, and halving (i.e., separating values above and below the median). For each of these functionalities, we present tight lower and upper bounds on the size of conclusive sets. Bounds are given both for conclusive sets composed of binary vectors and of general vectors. The bounds for general vectors are smaller than the bounds for binary vectors implied by the 0-1 principle. Our results hold also for comparator networks with unbounded fanout. Assume the network at hand has n inputs and outputs, where n is even. We present a conclusive set for sorting that contains $\binom{n}{n/2}$ nonbinary vectors. For merging, we present a conclusive set with $\frac n2 +1$ nonbinary vectors. For bitonic sorting, we present a conclusive set with n nonbinary vectors. For halving, we present $\binom{n}{n/2}$ binary vectors that constitute a conclusive set. We prove that all these conclusive sets are optimal. [ABSTRACT FROM AUTHOR]

The recently established computational equivalence between the traditional message-passing model and the mobile-agents model is based on the existence of a mobile-agents algorithm that simulates the execution of message-passing algorithms. Like most existing protocols for mobile agents, this simulation protocol works correctly only if the agents are fault-free. We consider the problem of performing the simulation of message-passing algorithms when the simulating agents may crash unexpectedly. We show how to simulate any distributed algorithm for the message-passing model in a mobile-agents system with k agents, tolerating up to f ≤ k − 1 crashes during the simulation. Two fault-tolerant simulation algorithms are presented, one for non-anonymous settings (i.e., where either the networks nodes or the agents or both have distinct identities), and one for anonymous systems (where both the network nodes and the agents are anonymous). In both cases, the simulation overhead is polynomial. Unlike the existing fault-free simulation algorithm, both our protocols are able to detect termination even if the simulated algorithm has no explicit termination detection. [ABSTRACT FROM AUTHOR]

We present the first location oblivious distributed unit disk graph coloring algorithm having a provable performance ratio of three (i.e. the number of colors used by the algorithm is at most three times the chromatic number of the graph). This is an improvement over the standard sequential coloring algorithm since we present a new lower bound of 10/3 for the worst-case performance ratio of the sequential coloring algorithm. The previous greatest lower bound on the performance ratio of the sequential coloring algorithm was 5/2. Using simulation, we also compare our algorithm with other existing unit disk graph coloring algorithms. [ABSTRACT FROM AUTHOR]

The focus of the present paper is on providing a local deterministic algorithm for colouring the edges of Yao-like subgraphs of Unit Disc Graphs. These are geometric graphs such that for some positive integers l,k the following property holds at each node v: if we partition the unit circle centered at v into 2k equally sized wedges then each wedge can contain at most l points different from v. We assume that the nodes are location aware, i.e. they know their Cartesian coordinates in the plane. The algorithm presented is local in the sense that each node can receive information emanating only from nodes which are at most a constant (depending on k and l, but not on the size of the graph) number of hops away from it, and hence the algorithm terminates in a constant number of steps. The number of colours used is 2kl + 1 and this is optimal for local algorithms (since the maximal degree is 2kl and a colouring with 2kl colours can only be constructed by a global algorithm), thus showing that in this class of graphs the price for locality is only one additional colour. Keywords and Phrases: Edge Colouring, Geometric Graphs, Unit Disk Graphs, Local Algorithm, Location Awareness, Wedge, Wireless Network. [ABSTRACT FROM AUTHOR]