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Item type:Publication, Access status: without files , Evaluation of cluster effect in mobile opportunistic networksThis paper analyses how data dissemination occurs in mobile Opportunistic Networks by evaluating the impact of different parameters such as density of neighbors, communication range, and speed. There exist several analytical models to evaluate the data dissemination time in OppNets. These models were developed based on a very strong assumption of uniform distribution of infected nodes. We prove that this assumption does not work for the whole spectrum of mobile OppNets. This paper shows our simulation results validated with our analytical model and discusses the impact of different parameters on data dissemination.Publicationtype: Conference Paper64 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Modeling of Data Dissemination in OppNets(IEEE, 2018-08); ; ; ; This paper focuses on modeling the charateristics of opportunistic networks (OppNets). The motivation of this work is to develop a model which is closer to the reality to represent the data dissemination in OppNets. This paper shows our preliminary results validating our model in OppNets scenarios which give an opportunity to exchange data among a group of people.Publicationtype: Conference Paper212 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Waiting Time Estimation for Periodic Traffic Sources in a Chain of Nodes(2017-10-11); ; ; Commercial-off-the-shelf (COTS) components are used in numerous communication systems and application fields for cost reduction. While this trend is adopted in various home and business scenarios, most components for safety critical systems are proprietary or significantly modified. This also applies to networks using IP over Ethernet. Hardly any accepted methods to certify safety critical communication networks with such COTS components exist. This paper presents a Queueing Theory based heuristic to estimate end-to-end delay times for IP and Ethernet based communication systems with periodic traffic sources. Traffic source models depending on few parameters, e.g. Interrupted- Poisson-Processes (IPPs), are used. Required input is information on the sources, network topology and routing, which can be easily obtained in some domains, e.g. for maritime vessels. The methods are therefore demonstrated for a ship network.Publicationtype: Conference Paper199 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , 73 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Optimal virtual network embedding: Energy aware formulationNetwork Virtualization is a key component of the Future Internet, providing the dynamic support of different networks with different paradigms and mechanisms in the same physical infrastructure. A major challenge in the dynamic provision of virtual networks is the embedding approach taking energy efficiency into account, while not affecting the overall Virtual Network (VN) acceptance ratio. Previous research focused on either designing heuristic-based algorithms to address the efficient embedding problem or to address the energy impact. This paper proposes an integer linear programming formulation, Energy Aware-Virtual Network Embedding-Node-Link Formulation (EA-VNE-NLF), that solves the online virtual network embedding as an optimization problem, striving for the minimum energy consumption and optimal resource allocation per VN mapping. Two different objective functions are proposed: (i) addressing primarily the resource consumption problem - Bandwidth Consumption Minimization (BCM); (ii) addressing primarily the energy consumption problem - Energy Consumption Minimization (ECM). The performance of each objective function is evaluated by means of simulation and compared with an existing objective function, Weighted Shortest Distance Path (WSDP), that is considered state of the art of the resource allocation problem. The simulation results show that the objective function BCM reduces the energy consumption of the physical network by 14.4%, and improves the embedding factor by 4.3%, consuming almost the same amount of resources as requested, and slightly worsening the VN acceptance ratio by 2.3%. ECM reduces the energy consumption of the physical network by 31.4% and improves the embedding factor by 4.1%, without affecting the VN acceptance ratio when compared to WSDP.Publicationtype: Journal Article148 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Using Demisubmartingales for the Stochastic Analysis of NetworksStochastic network calculus is the probabilistic version of the network calculus, which uses envelopes to perform probabilistic analysis of queueing networks. The accuracy of probabilistic end-to-end delay or backlog bounds computed using network calculus has always been a concern. In this paper, we propose novel end-to-end probabilistic bounds based on demimartingale inequalities which improve the existing bounds for the tandem networks of GI/GI/1 queues. In particular, we show that reasonably accurate bounds are achieved by comparing the new bounds with the existing results for a network of M/M/1 queues.Publicationtype: Journal Article98 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Optimal virtual network embedding: Node-link formulationNetwork Virtualization is claimed to be a key component of the Future Internet, providing the dynamic support of different networks with different paradigms and mechanisms in the same physical infrastructure. A major challenge in the dynamic provision of virtual networks is the efficient embedding of virtual resources into physical ones. Since this problem is known to be NP-hard, previous research focused on designing heuristic-based algorithms; most of them either do not consider a simultaneous embedding of virtual nodes and virtual links, or apply link-path formulation, leading to non-optimal solutions. This paper proposes an integer linear programming (ILP) formulation to solve the online virtual network embedding problem as a result of an objective function striving for the minimization of resource consumption and load balancing. To this end 3 different objective functions are proposed and evaluated. This approach applies multi-commodity flow constraint to accomplish a node-link formulation that optimizes the allocation of physical network resources. This proposal is evaluated against state of the art heuristics. The performance of the heuristics related to Virtual Network (VN) request acceptance ratio is, at least, 30% below the one of the Virtual Network Embedding Node-Link Formulation (VNE-NLF) method. From the three cost functions evaluated, the Weighted Shortest Distance Path (WSDP) is the one which embeds more VNs and also requires, on average, less physical resources per embedding.Publicationtype: Journal Article119 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A re-optimization approach for virtual network embedding(Springer, 2013-09-02); ; ; ; Network Virtualization is claimed to be a key component of the Future Internet by enabling the coexistence of heterogeneous (virtual) networks in the same physical infrastructure, providing the dynamic creation and support of different networks with different paradigms and mechanisms in the same physical network. A major challenge in the dynamic provision of virtual networks resides in the optimal embedding solution of virtual resources into physical ones. Since this problem is known to be NP-hard, previous research focused on designing heuristic-based algorithms; most of them do not consider either a simultaneous optimization of the node and the link mapping or the re-optimization of VNs, leading to non-optimal solutions. This paper proposes an extension of Virtual Network Embedding - Node-Link Formulation to support the re-optimization of existing VNs and to provide the optimal bound. It also presents an evaluation of the proposed approach when applied to a previous heuristic in the literature. Simulation experiments show significant improvements when using the VN re-optimization process: not only the bandwidth consumption have been reduced by 17.5%, but the same is true for the maximum utilization levels on the CPU and on the memory. © Institute for Computer Sciences, Social Informatics and Telecommunications Engineering 2013.Publicationtype: Conference Paper132 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , QoS impact of hierarchical routing in multi-channel sensor networksEnabling integration of Wireless Sensor Networks (WSN) and smart objects with the Internet is an important milestone towards the so called Internet of Things. Providing these networks with QoS capabilities is crucial for emerging applications that have end-to-end requirements on the border wireless network domain. Impairments such as delays and losses are heavily influenced by the quality of the communication channels, the routing, the MAC protocol and the interactions of these influential factors. In this work we report on a hierarchical routing scheme for sensor networks with multi-channel radios aiming at improving QoS. The scheme decouples the aforementioned influences: The MAC-protocol is responsible for a scheduling in a set of nodes called a cluster. Neighboring clusters use different frequencies. The routing is done at the level of clusters. The (distributed) algorithms executed by the network nodes to support this architecture are evaluated against optimal solutions for clustering, frequency allocation and routing derived from Integer Linear Programming. © Institute for Computer Sciences, Social Informatics and Telecommunications Engineering 2013.Publicationtype: Conference Paper67 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Virtual network mapping - an optimization problem(Springer, 2012-07-27); ; ; ; Network Virtualization is claimed to be a key component of the Future Internet by enabling the coexistence of heterogeneous (virtual) networks on the same physical infrastructure, providing the dynamic creation and support of different networks with different paradigms and mechanisms in the same physical network. A major challenge in the dynamic provision of virtual networks resides on the efficient embedding of virtual resources into physical ones. Since this problem is known to be -hard, previous research focused on designing heuristic-based algorithms; most of them do not consider a simultaneous optimization of the node and the link mapping, leading to non-optimal solutions. This paper proposes an integer linear programming formulation to solve the virtual network embedding problem, as a simultaneous optimization of virtual nodes and links placement, providing the optimal boundary for each virtual network mapping. A link∈-∈node formulation is used and the multi-commodity flow constrain is applied. In addition, a heuristic algorithm for virtual network embedding is also proposed and compared against the optimal formulation. The performance of the integer linear programming formulation and of the heuristic is evaluated by means of simulation. Simulation experiments show significant improvements of the virtual network acceptance ratio, in average additional 10% of the virtual network requests are accepted when using the integer linear programming formulation, which corresponds, in average, to more 7 virtual networks accommodated on the physical network. © 2012 ICST Institute for Computer Science, Social Informatics and Telecommunications Engineering.Publicationtype: Conference Paper35