The coronavirus pandemic continues to represent widespread panic, and global initiatives are focused on treating and limiting its spread. Contact tracing promises to help fight this pandemic through early detection of possible contagion events. In this context, several mobile applications have been proposed to try to identify the contact cases of a person who tested positive for COVID-19. In total, 32 countries have developed such applications and are using them as a strategy that may flatten the pandemic curve. These applications can also be adopted to combat future communicable diseases among humans. However, most of these applications do not fully respect the preservation of the privacy of users. That’s why, the adoption of these applications is being held back in many countries. Motivated by the need to protect user privacy, we analyze some of these applications. We demonstrate that they collect sensitive data which represents a violation of user privacy. At the end, we present several major recommendations that can serve as a reference, contributing to the development of privacy-preserving contact tracing applications.

Recent advancements in avionics and electronics systems led to the increased use of Unmanned Aerial Vehicles (UAVs) in several military and civilian missions. One of the main advantages that makes UAVs attractive is their ability to reach remote regions that are inaccessible to human operators, i.e. provide new aerial perspective in visual surveillance. Autonomous visual surveillance systems require real time anomalies detection. However, there are many difficulties associated with automatic anomalies detection by an UAV, as there is a lack in the proposed contributions describing abnormal events detection in videos recorded by a drone. In this paper, we propose an anomaly detection approach in a surveillance mission where videos are acquired by an UAV. We combine deep features extracted using a pretrained Convolutional Neural Network (CNN) with an unsupervised classification method, namely One Class Support Vector Machine (OCSVM). The quantitative results obtained on the used dataset show that our proposed method achieves good results in comparison to existing technique with an Area Under Curve (AUC) of 0.93.

In recent years, the diffusion of electric vehicles(EVs) is of great importance in the road transport and automotive sectors. Reducing electricity consumption and increasing battery autonomy are actually motivating vehicle manufacturers to focus their attention on the EV concept. The evaluation of EV performance through realistic scenarios in traffic simulations is still a key issue. In fact, the road traffic Simulator Simulation of Urban Mobility (SUMO) integrates an energy model for calculating the EV energy consumption. However, this model underestimates the energy consumption values in the real world. In this paper, we intend to investigate the energy consumption models existing in the literature. Then, we assess the performance of the existing energy model in SUMO through a set of simulation scenarios. Finally, we present the main requirements for a realistic, accurate and scalable energy model to estimate the instantaneous energy consumption for EVs.

Unmanned Aerial Vehicles (UAVs) have known much popularity for dangerous missions for human operators or for applications which do not need human intervention (such as monitoring and surveillance of physical infrastructures and interest areas). They operate in frequency bands (IEEE L-Band, IEEE S-Band, and ISM band) shared with other users. Accordingly, these frequency bands have become overcrowded and UAVs may face the issue of spectrum scarcity. Furthermore, there are particular difficulties associated with aeronautical communication links. Cognitive radio (CR) has emerged as a promising strategy for resolving the problems caused by scarce spectrum. It checks the spectrum availability and allows the adjustment of the transmission parameters. The aim is to opportunistically use spectral bands with minimum interference to applications or other users. In this paper, we present a centralized CR based frequency allocation scheme for UAV-Ground Control Station (GCS) communication in surveillance applications within an urban environment. In the proposed model, the GCS monitors and allocates available WiMAX frequencies using CR and Software Defined Radio (SDR). If no WiMAX frequency is available at a given time, the Wi-Fi will be used. Therefore in the worst case, our approach will have the same performance as when the Wi-Fi is only used for UAV-GCS communication.

In recent years, a large number of researchers investigate the conception of systems that use a unique Unmanned Ariel Vehicles (UAV) or multiple independent UAVs to conduct civil or military missions, with minimal human intervention. In this paper we focus on using multiple UAVs to cooperatively monitor a crowded area. Communication in such UAVs network is an ongoing project. Due to the lack of proper communication standards and rules, designing a reliable communication model is essential for: (i) multi-UAV coordination, (ii) efficient bandwidth sharing according to data priority and urgency and (iii) avoiding useless transmission of the same data by multiple UAVs. To address the above challenges, we propose a centralized data-oriented communication architecture for crowd surveillance allocations using an UAV fleet. The Ground Control Station (GCS) is used as a central coordinator to manage bandwidth usage for the UAV fleet in its coverage area. To allow UAVs to send priority messages urgently to the GCS, we define two classes of urgent messages: critical state and important result. The class of the data as well as other relevant information about the detected event will be used by the GCS to authorize or not UAV data transmission and hence to optimize the bandwidth usage efficiency.

The attempts to reduce vehicle's CO2 emissions and fuel consumption are actually motivating the manufacturers in the transport and automotive sectors to focus their interests on Electric Vehicle (EV) concept. Battery autonomy and charging process are still a big issue for that kind of vehicles. The evaluation of EV's instantaneous energy consumption through realistic scenarios and based on consistent energy models are needed to take step forward on these issues. In this paper, we provide a deep insight on EV consumption dynamics and make a review of the energy model implemented in SUMO, one of the most popular traffic simulation framework used to evaluate vehicular technologies and strategies. We propose a set of energy consumption estimation improvements and show through simulation the achieved improvements in terms of accuracy compared to the sumo implementation.

This work presents algorithms to extend tenant Virtualized Network Functions Forwarding Graphs (VNF-FG) to embed new networking functions and introduce gradually additional services into the already deployed tenant dedicated slices. The related service graph extension problem is addressed through an Integer Linear Programming (ILP) algorithm that serves as a reference for performance comparisons with a proposed heuristic algorithm. An eigendecomposition approach is proposed, evaluated and compared.

Many studies aim at introducing recent technologies in Electric Vehicles (EVs) to accurately estimate their energy consumption. In this paper, we reviewed the current energy consumption model in SUMO. This latter is known to be the most reliable traffic simulator used for evaluating traffic management and vehicular technologies. We proposed a set of improvements that must be applied on SUMO energy model and we focused on integrating the ambient temperature factor. Finally, simulation results show the accuracy of the proposed solution from different perspectives.

The transport model of the Named Data Networking (NDN) architecture introduces several new features, especially content can be retrieved from multiple sources and through multiple paths and may be stored in different in-network caches. These distinguished features make the traditional host-to-host TCP/IP congestion control schemes inconsistent with the NDN's communication model. In this paper, we describe and evaluate IRNA: a Hop-By-Hop Interest Rate Notification and Adjustment scheme. To address the above issues, IRNA controls the outgoing Interest queue occupancy at every NDN router. When the queue size exceeds or falls below a specified threshold, IRNA signals it towards downstream nodes by explicitly specifying the suitable Interest receiving rate. Consumers and routers along the path adjust their Interest sending rates according to the available rate specified in this notification. We evaluated IRNA through simulation and our results show that IRNA reacts quickly to congestion events while maintaining a proper bandwidth usage. Moreover, IRNA guarantees bandwidth fair sharing between consumers.

Today, Cloud Computing architectures offer a cost-efficient services delivered for business, scientific and legal organizations. These structures are used as a guideline to understand the Cloud component, services, actors and interactions. However, few Cloud Computing architectures are proposed and used as references to build a Cloud infrastructure. Most of these models does not treat and burst security layers despite the fact that it presents the most important concerns in the Cloud. The aim of this paper is to propose a new end-to-end reference architecture based on a novel classification of security issues in Cloud Computing environment. To do so, we are going to explore the fundamental concepts of Cloud. We will study and propose a novel actor-based classification of security issues. We will model a Cloud reference architecture from security perspective and we will study in depth security and defense in the Cloud provider tier. We will add a management layer in order to refine our design. To the best of our knowledge, our proposal provides the first Cloud Computing reference architecture actor-based from both security and management perspectives in research field.

Named Data Networking (NDN) is an Information Centric Networks (ICN) solution that has recently attracted significant attention. NDN changes the Internet communication paradigm from the host-to-host IP model, to a name based communication model. In NDN, the requested Data can be retrieved from different sources and through multiple paths. This distinguished feature of NDN makes the traditional end-to-end congestion control schemes flagging with this new architecture. In this paper, we present a Hop-by-hop congestion control mechanism to regulate the Interest rate between the consumer and the congested router. Each NDN router continuously monitors its outgoing queues occupancy. When the queue size exceeds or falls below a specified threshold, an explicit notification is sent to downstream routers and consumers. The consumer and routers along the path then react by adjusting their Interest sending rates according to the available rate specified in the received notification. We prove the efficiency of the proposed solution and its ability to reduce the congestion impact and to maintain fairness per consumer. We highlight the advantages of our solution using different scenarios implemented in ndnSIM.

Network Functions Virtualization (NFV) has been revolutionizing and improving the way networking services are deployed but also requires the dynamic scaling of resources during the lifecycle management of Virtual Network Functions (VNFs) with increasing service demand. We propose an Integer Linear Programming (ILP) approach and a Greedy heuristic to address this NP-Hard scaling problem. Both horizontal (scale out/in) and vertical (scale up/down) scaling are considered and the scalability of the ILP is addressed by reducing the number of candidate hosts in the search space. Extensive simulations evaluate the performance of the algorithms in successful scalings and VNF migrations and highlight the importance of using the algorithms to tidy up the infrastructure to accept more users. The results show that the ILP can outperform the Greedy heuristic if appropriate actions are selected.

Named Data Networking (NDN) is an Information-Centric Networking architecture that has recently attracted significant attention. NDN rethinks the Internet communication paradigm around the name of the data instead of its location. In Content-Oriented architectures, in-network caching enables data retrieval from different network nodes and may result in frequent data sources changes and wide RTT fluctuations during a flow. Since NDN architectures use Interest retransmission timer at the scale of network RTT estimations, this would generate erroneously premature timeouts events resulting in unnecessary Interests retransmission. In this paper, we tackle the Interest retransmission problem. We first analyze the impact of temporary caches on the number of timeouts events. Then we introduce “Source Change Notification” to address this issue. A preliminary evaluation has been conducted by means of the ndnSIM simulator. Our evaluation results show that our proposal succeeds in preventing unnecessary Interest retransmission when data providers change.

In the context of multi-rate communication, the throughput-based multicast routing that aims at maximizing the end-to-end throughput is very different from the commonly adopted delay-based multicast routing that aims at minimizing the end-to-end delay. Definitely, the delay-based approach is not suitable for applications that need to transfer large amounts of data (e.g. grid applications). In view of that, we introduce in this paper the first distributed routing strategy that allows high-throughput multicast in multi-rate IEEE802.11 networks. The new mesh-based routing, called the Protocol for End-to-end Multicast Session Efficiency (PEMSE), exploits the rate-diversity (MUD) and on the broadcast-nature of the wireless medium (WBA). It aims at: i) considering the effect of the number of transmissions/retransmissions, required to exploit the MUD, on the end-to-end multicast throughput and ii) establishing the routing structure that guarantees the best end-to-end multicast throughput. Simulations prove that PEMSE achieves considerable throughput improvement compared to the PUMA [11] routing protocol. They also show that PEMSE attains reasonable delays and delivery ratios.

In this paper, we introduce a new routing strategy that allows high-throughput and channel-aware multi-rate multicast in wireless networks. This new routing strategy, based on the so-called End-to-end Multicast Session Efficiency (EMSE), is founded on the multi-user diversity (MUD) and the wireless broadcast advantage (WBA) features. It aims at: i) joining users that provide the best-received multicast throughput, ii) guaranteeing the use of homogenous capacities, iii) considering the effect of the transmission/retransmission number needed to exploit the multi-rate diversity on the routing throughput and iv) constructing the multicast structure composed of paths that give the best end-to-end throughput. Compared to other routing strategies and multicast schemes, the new routing algorithms show considerable improvement in terms of the average throughput and an important reduction in the relays number needed to convey the multicast data.

Nowadays, content retrieval is marking the Internet usage. User communications are no longer tied up to host interconnection. Information Centric Networking (ICN) models are proposed to cope with these changes. The new paradigm redesigns the Internet architecture to bring out content to the first level. Over the last decade, many key projects have proposed a large solution spectrum to rebuilt networking primitives focused on the content. One important and direct challenge of this shift is the large amount of routing states due to identifying contents rather than hosts. In this paper, we focus especially on DONA, one of the first ICN architecture, and analyse the required memory space to store routing states. Our study shows that today's technologies are not able to satisfy the content routing needs. Thus, we propose an enhancement of DONA called BADONA to deal with this problem. It uses the Bloom filter to drastically reduce the usage of the memory space. Finally, we evaluate our proposal performances to underscore its contribution.

Cars cruising for parking adds a non negligible amount to traffic congestion and CO2pollution. Hence, good parking management policies are required to reduce such discomfort. In this paper, we address this problem from two sides. First, we consider how local parking authorities called parking coordinators (PC) can optimize the distribution of the slots they manage through a full cooperation between them. Second, we model the problem as a congestion game, where vehicles act as players who will eventually choose the best parking garage for them, while minimizing the whole network cost. We study the effectiveness of both schemes (i.e, PC-aware and game theoretic approaches) in various contexts and compare them with the reference centralized model as well as a greedy approach. Simulation results show that our proposals provide high request satisfaction ratio, close to the optimal baseline approach and outperform the greedy method up to 30%, while ensuring a fair distribution of slots through the network.

Multicast routing is a fundamental issue in wireless networks and related routing strategies should select the lowest number of parallel conflicting transmissions. However, current works on this problem accounts only for conflicts occurring within the transmission ranges of the nodes. Particularly, no work is interested in studying conflicting transmissions while using multi-rate concurrent multicast transmissions. In this paper, we develop a conflict-aware routing model, which aims at increasing the probability of scheduling conflict-free transmissions and improving the throughput by extremely exploiting the network availabilities in terms of link capacities, using different rates. The suggested conflict-aware routing strategy is implemented by means of a set of greedy heuristic algorithms. This strategy, called the CAware routing strategy, is “generic” because it can be coupled with any throughput-based routing metric or any routing structure. The proposed algorithms are studied to justify their performance trends and to show that conflict-awareness gives considerable routing benefits.

The emergence of new kinds of applications and technologies (e.g., data-intensive applications, server virtualization) has led to a better utilization of the network resources. However, it has also led to more bandwidth consumption and more congestion especially inside data center networks. Thus, researchers are focusing again on TCP and Active Queue Management (AQM) mechanisms in order to better control congestion and to cope with application requirements in terms of end-to-end delay [1], [2], [3]. Recently, we proposed a new AQM mechanism (called α_SNFAQM) that uses traffic prediction to accurately detect future congestion and to proactively act upon it [4]. In this paper, we develop an analytical model to assess the effect of α_SNFAQM on TCP. The study proves that this AQM is efficient enough to stabilize queue size in routers/switches, and thereby allowing to control end-to-end packet delay. These results have been also validated by simulations for a topology with multiple bottleneck links. They show that α_SNFAQM outperforms other AQM schemes like RED, PAQM and APACE in stabilizing instantaneous queue length, while keeping a high utilization of the links and the same packet loss rate.

Achieving efficient QoS routing is one of the major concerns in multi-radio multi-channel wireless mesh networks (WMNs). Due to interference among links, bandwidth in these networks is neither a concave nor an additive metric. Thus, choosing the highest-throughput path among all feasible ones is a very challenging task. We propose in this paper a new routing metric which strikes a balance between the quality of wireless links and the resulting inter-flow and intra-flow interference introduced using such links on specific channels. Our metric does not necessarily choose the best path in terms of throughput. It selects a high-throughput path with low inter-flow and intra-flow interference by making a judicious use of different channels. Simulation results show that our routing metric significantly outperforms previously proposed metrics especially in large-scale WMNs. An improvement up to 20% of the total network throughput is particularly observed when multiple concurrent flows are considered in the network.

ABSTRACT Distributed denial‐of‐service (DDoS) attacks present an increasing threat to the global inter‐networking infrastructure. While entropy schemes are highly robust to diverse network conditions, they remain vulnerable to distribute attacks that are similar to legitimate traffic. With the knowledge that the objective of a DDoS attack is to saturate as soon as possible the resources of the target, this would engender an unexpected disproportion between the number of received packets and the number of connections. However, in the case of flash crowds, an increase in the number of packets is always accompanied by an increase in the number of connections. In this work, we used joint‐entropy that quantifies the degree of disproportion to detect traffic anomalies. We investigate a class of intelligent attacks, which, unlike high‐rate attacks, are difficult for entropy schemes to detect. The experimental results indicate that our joint‐entropy scheme can detect this type of attacks accurately. Compared with an entropy‐based scheme, the improvement is 40% for the distributed attacks. Copyright © 2011 John Wiley & Sons, Ltd.

Evolving from a document-centered into a service and data-centered World Wide Web, Web of data, requires a better user's digital identity protection and management. The permanence nature of digital identity entails loss of user's control over distributed identity attributes and privacy breaches. In this paper, we propose an innovative Stop-Dissemination mechanism that is built on the basis of data expiration date techniques coupled with the promising content centric networking (CCN) capabilities. Two use cases are detailed to explain the mechanism in order to have low permanence of federated digital identity documents.

Nowadays, wireless 802.11 access points (APs) are increasingly widespread in urban and sub-urban areas. Besides part of them offer free access, hence such infrastructure can provide intermittent Internet access to vehicles for opportunistic applications like software or digital maps updates, vehicle diagnostic reporting, and certificates/pseudonyms renewing.

Abstract Common key management schemes are hard to deploy inad hocnetworks because of their infrastructure‐less nature and dynamic topology. In this paper, we propose a hybrid key management architecture that is adapted forad hocnetworks. The proposed architecture is based on a clustering algorithm called RECA that we have designed for security purposes inad hocnetworks. RECA allows an efficient division of the network into clusters managed by trustworthy clusterheads that are supervised by a reputation system. The hybrid key management architecture exploits this division for scalability and availability of security services. It considers each clusterhead as a certification authority (CA) for its members and implements a totally distributed CA over only clusterheads. Simulations results show that the proposed solution enhances security services availability in comparison with existing solutions. Copyright © 2009 John Wiley & Sons, Ltd.

Distributed Denial of service (DDoS) attack has become one of the most serious threats to the Internet. DDoS attack can be considered a system anomaly or misuse from which abnormal behaviour is imposed on network traffic. Network traffic characterization with behaviour modelling could be a good indication of attack detection witch can be performed via abnormal behaviour identification. Moreover, it is hard to distinguish the difference of an unusual high volume of traffic which is caused by the attack or occurs when a huge number of users occasionally access the target machine at the same time. While previous work has demonstrated the benefits of entropy-based anomaly detection, there has been little effort to understand the detection power of using joint entropy analysis of multiple traffic distributions. We observe that the time series of IP-flow number and aggregate traffic size are strongly statistically dependant. The occurrence of attack affects this dependence and causes a rupture in time series of joint entropy values. Experiment results show that this method could lead to more accurate and effective DDoS detection.

In a mobile ad hoc network, link failures and route changes occur frequently. Mistaking these events for congestion degrades TCP performance. Hence, TCP congestion control mechanisms should not react to such loss events. This paper deals with an enhancement of the congestion control mechanism, called TCP Adaptive RTO (TCP AR). This proposal relies on two basic concepts. First, it distinguishes routes failures from network congestion based on transport layer feedbacks. Second, during timeout, it adjusts the RTO's value to network conditions. We evaluate this new technique using different simulations scenarios, to compare its throughput gain, fairness and friendliness to those of TCP New Reno.

ADMA represents an Autonomous Decentralized Management Architecture designed to provide Mobile Ad Hoc Networks (MANETs) with autonomic principles. It allows the network to configure and reconfigure itself under environment changes without any human intervention. Our solution operates in a peer-to-peer manner and does not require any centralized entity to perform network management functions. Each mobile node implementing ADMA components is able to take the appropriate decision based on predefined high level policies and collected monitoring information. We present in this paper the basic components of an ADMA node. Then, we provide a simple self-configuring case study of our design considering Voice over IP (VoIP) as a test application. Simulation results show an improvement of the VoIP delay and loss rate while applying predefined policies.

Clustering in ad hoc networks consists of dividing the network into clusters managed by clusterheads. This technique has been used for different goals. However, as far as we know, no existing clustering algorithms have considered the existence of malicious nodes for clusterheads election and maintenance. Consequently, we propose a REputation based Clustering Algorithm (RECA) that aims to elect trustworthy, stable and high energy clusterheads that can be used to manage the security of the network. Simulation results have shown that RECA converges to a stable and convenient network division into clusters with no untrustworthy clusterheads and mainly one hop members.

Clustering in ad hoc networks consists in dividing the network into clusters (groups) managed by elected nodes called clusterheads. This technique has been used for different goals as routing efficiency, transmission management and information collection. As far as we know, no existing clustering algorithms have taken into account the existence of malicious nodes for clusterheads election and maintenance. These nodes can lie to be elected as clusterheads. Consequently the network might be managed by most of them. To solve this problem, we propose a reputation based clustering algorithm (RECA) that aims to elect trustworthy, stable and high energy clusterheads that can be used to manage the security of the network. Simulations were conducted to evaluate RECA performances in the presence of liars. Results show that it converges to a stable and convenient network division into clusters with no untrustworthy clusterheads and mainly one hop members.

With current network simulators, simulation results are obtained from flat trace files via sequential data access. To speed up simulation output analysis, we propose to store the simulation traces into data warehouse. Our proposed framework relies on a three-layer architecture, with the intermediary database layer serving the trace file post processing services. The trace files are accessed through SQL-like queries which greatly enhances the flexibility of the post processing tools. Furthermore, the database paradigm allows to separate the packets data from the nodes send and receive operations and thus to remove redundant information between simulation events. The global system relies on a new trace file format based on the popular XML language. XML pointers are used to create relationships between data so that post processing tools can navigate into simulation outputs. The tests are carried out under the MonetDB database. The obtained results show considerable response time improvement compared to traditional sequential access mode.

Wireless and wired networks have commonly evolved separately. However with the integration of quad-play services (i.e., mobile/fixed voice, video, and data) into a single network infrastructure the provisioning of end-to-end connections spanning both the wireless and the wired domains becomes an important issue. In this paper two solutions are proposed for implementing an integrated end-to-end signaling for establishing QoS-guaranteed connections in integrated WiMAX and MPLS based networks. The two solutions are based on the integration of WiMAX management messages and RSVP-TE signaling. Their main difference consists in the way flow WiMAX message and RSVPTE signaling are triggered and coordinated.

Active Queue Management (AQM) policies are mechanisms for congestion avoidance, which pro-actively drop packets in order to provide an early congestion notification to the sources. Random Early Detection (RED), the defacto standard and its different flavors have been proposed as simple solutions to the AQM problem. However, these approaches require manual tuning and fail to accurately capture variations in the input traffic, thereby resulting in unstable behavior. α_SNFAQM is a new AQM mechanism that uses a neurofuzzy prediction method (α_SNF) to capture traffic variation and accurately detect the future congestion. It distinguishes (i) severe congestion and (ii) light congestion. We compare the performance of α_SNFAQM with other AQM schemes like RED, PAQM and APACE in a bottleneck link. Simulation results have shown that α_SNFAQM outperforms other AQM schemes in stabilizing the instantaneous queue length, reducing packet loss ratio while keeping a high utilization of the link.

In this paper, we propose a new QoS architecture for PMP 802.16 systems operating in TDD mode over wirelessMAN-OFDM physical layer. It includes a call admission control policy and a hierarchical scheduling algorithm. The CAC policy we propose adopts a min-max fairness approach making efficient and fair use of available resources. The proposed scheduling algorithm flexibly adjusts uplink and downlink bandwidth to serve unbalanced traffic while considering adaptive modulation and coding (AMC) scheme. The efficiency of the proposed QoS architecture is revealed through simulation.

The comparison and validation of MANET (mobile ad-hoc network) simulators is a difficult and little covered research area because the internal of these tools are complex. The lack of work and visibility in the domain often arouse users' negative feelings about simulation. In this article, we propose a framework dedicated to the validation, the comprehension and the analysis of MANET simulators. The system can process trace files generated by different versions of a simulator or different simulators. The solution is based on software instrumentation and the use of a standard trace format. It proposes three types of analysis: the representation of the network activity with timelines, the plotting of network metrics and the validation against the 802.11 standard specifications.

The availability of interactive multimedia applications (skype, wengo, LiveCom, etc.) is going to modify the usage of future Internet. Such Internet is likely to be more heterogeneous, consisting of different islands of ad-hoc networks. This argues for the growth of interactive applications traffic at the ad-hoc networks level. Providing Quality of Service (QoS) support, in particular low loss rate and low end-to-end delay, in such networks is a challenging task. Limited bandwidth resource and high mobility are two major characteristics of such networks. Moreover, the link breakage rate is high, which leads to high loss rate in the network. In the literature, researches generally span over routing protocols and MAC Layer mechanisms [1] to guarantee few QoS aspects by introducing signalling traffic.

The development of WLANs in general and of Wi-Fi (802.11b standard) in particular, emerged these two last years as a technology support of public access to the Internet. We think that the potential role of Wi-Fi hotspots, those wireless networks deployed in public environments such as airports, hotels and conference centres, is enormous and will give a new breath to the mobile commerce market. However, the m-commerce still faces challenges, due to the immaturity of these new technologies and where security represents one of its major issues.

In this paper we propose an approach, combining the SET protocol with the TLS/WTLS protocols in order to enforce the security services over WAP 1.X for payment in the m-commerce. We propose to implement the additional services of the SET protocol as the confidentiality of the payment information between the buyer and the payment gateway and the data integrity. However, we use WTLS certificates instead of the SET certificates. This allows to avoid the SET certification heaviness. Moreover, this approach eliminates the "WAP gap" since the payment information would not be decrypted within the WAP gateway nor within the seller side.

The nature of Ethernet Multiple Access Control (CSMA/CD) makes it impossible to get a deterministic medium access time to guarantee real time constraints. We propose a new Ethernet Access protocol called EDF-CSMA which is inspired from the optimal scheduling centralized algorithm EDF (Earliest Deadline First). This protocol compatible with CSMA, gives guaranteed prediction to real-time messages and performs better guarantee results than protocols in previous works such as: CSMA-DCR, DOD-CSMA/CD, VTCSMA and RTCC. We also extend this protocol to realistic context, where it treats at the same time hard real time messages with deadline guarantees, soft real time messages with minimizing their deadline missing and non real time messages to be sent in finite time.

As the satellite technology will be one of the main components of the next generation Internet (NGI), a naturally occurring question concerns the feasibility of providing an efficient satellite-based Internet access. In this paper, we are interested in the problem of the planning of satellite-terrestrial hybrid networks for the multicast transfer. We first develop an architectural model for such type of networks, then we define the problem and we propose a planning heuristic that determines the suboptimal positions of satellite uplinks in a given terrestrial network. The proposed method minimizes the mean cost (the number of branches) of multicast trees for the unreliable multicast and the mean packet transfer delay for the reliable multicast. In addition, we develop a configuration policy of PIM-SM in hybrid networks concerning the choice of the list of rendezvous points (RPs) and the switching from the RP-routed tree to the shortest path tree. The obtained results demonstrate the ability of the proposed methods (the planning heuristic and the PIM-SM configuration policy) to improve the multicast performance criteria and to determine effectively the satellite uplink positions using PIM-SM combined with UDLR (unidirectional link routing).

With the emergence of new multimedia applications and the large standardization effort of packet telephony products, a large volume of small packet traffic flows in the network. It is expected to get worse with the popularity of VoIP applications. To mitigate the impact of small packets we propose the aggregation of packets present in the output queue and which have the same forwarding equivalence class, such as those which will leave a routing domain from the same node (an egress node). The set of aggregated packets will be subsequently treated as a single packet, thus requiring smaller processing overhead at intermediate routers. We report the results of several simulations that evaluate the performance benefits of aggregation. We note that aggregation keeps the same behavior as pure FIFO. Thus it doesn't disturb the aggregator router behavior. It saves CPU processing time and buffer space at intermediate routers, thus improving the overall network performance.

In a previous work we have proposed the PD (proportional and derivative) algorithm, which is an explicit algorithm for ABR flow control in ATM networks. The performance study of this algorithm has shown that on one hand, it achieves a full utilization of network links and the fairness in bandwidth allocation. On the other hand, the PD algorithm ensures good buffer occupancy with respect to the fixed threshold. In this study, both a simple network topology and the GFC1 topology have been considered. The PD algorithm implies control gains in the calculation of the supported rate, thus in this paper, we are interested in investigating the effect of the control gain choice on the stability of the system, in terms of buffer occupancy and source rate behaviour, when the PD algorithm is applied.

In a real-time distributed transactional system, customers generate transactions, which should be executed on different servers. Transactions are scheduled according to the (earliest deadline first) EDF discipline. To get a global view of the system, the consensus algorithm has been considered. In this paper, a mathematical model is developed to obtain the average stay time of a transaction within the system. This model introduces a bulk arrival M/G/1 station with K classes of customers where bulks are considered according to the FIFO discipline, customers are scheduled according to EDF within a group, and the algorithms operation is taken into account according to the head of line discipline. The response time distribution is also computed. This has allowed us to determine the optimal minimal interconsensus for a given consensus duration, the deadline miss probability and the minimum value to attribute to a transaction deadline in order to guarantee a given probability that the transaction does not miss its deadline.

In a real-time distributed transactional system, customers generate transactions, which should be scheduled to be executed on different servers. The transactions must be executed before their deadlines. To schedule these transactions the circulating multisequencer and the consensus algorithms have been considered to obtain a global view of the system. Mathematical models are developed to obtain the average stay time of a transaction within the system. The response time distribution is also computed. This allowed us to determine the minimum relative deadline, to affect to a generated transaction, to guarantee a given probability p that the transaction does not miss its deadline. This study shows that the circulating multisequencer algorithm presents better results.

Store-and-forward packet switched networks are subject to congestion under heavy load conditions. In this paper a distributed drop and throttle flow control (DTFC) policy based on a nodal buffer management scheme is proposed. Two classes of traffic are identified: "new" and "transit" traffic. Packets that traveled over one or more hops are considered as transit packets. Packets that are candidates to enter the communication network are considered as new packets. At a given node if the number of allocated buffers is greater than a limit value, then new traffic is rejected, whereas transit traffic is accepted. Indeed, if the total buffer area is occupied, transit traffic is also rejected and, furthermore, it is dropped from the network. This policy is analyzed in the context of symmetrical networks. A queueing network model is developed whereby network throughput is expressed in terms of the traffic load, the number of buffers in a node and the DTFC limit value. Optimal policies where the limit value is a function of the traffic load are found to prevent network congestion. Furthermore, they achieve a very good network throughput even for loads fifty times beyond the normal operating region. Moreover, suboptimal, easy to implement fixed limit policies offer satisfactory results.

Abstract Large packet switching computer networks on the order of hundreds or thousands of nodes will soon emerge to handle the fast‐growing demands in data communication and resource sharing among various information processing systems around the world. The network topology design problem has long been recognized as extremely complex and very quickly becomes unmanageable as the size of the network increases. Existing heuristic design procedures are quite efficient for the design of small to moderate‐sized networks (25–75 nodes); however, they become very costly and even prohibitive when dealing with large networks. A design methodology based on the hierarchical clustering of the network nodes is presented in this paper in order to alleviate the computational cost involved in the design. More specifically, the emphasis is on the determination of a clustering structure which minimizes the computational cost of the design. Such a cost is assumed to have a polynomial growth with the number of nodes in the subnet to be designed. We present optimum results both for the number of clusters, number of superclusters, etc., and for the number of hierarchical levels. An expression for the average delay of a message in such a hierarchical network is also provided in terms of the average delays in the subnets composing the network. This decomposition leads to the design of smaller subnetworks for which we can utilize present design strategies.

Nodal storage limitations in a store and forward computer network lead to blocking; this results in degradation of network performance due to the loss or retransmission of blocked messages. In this paper, we consider several schemes for sharing a pool of buffers among a set of communication channels emanating from a given node in a network environment so as to make effective use of storage in a variety of applications. Five sharing schemes are examined, analyzed, and displayed in a fashion which permits one to establish the tradeoffs among blocking probability, utilization, throughput, and delay. The key to the analysis lies in the observation that the equilibrium joint probability distribution of the buffer occupancy obeys the well-known product form solution for networks of queues. The study indicates advantages and pitfalls of each of the sharing schemes. We observe, in general, that sharing with appropriate restrictions on the contention for space is very much desirable.