Browsing by Author "Farahmand, Farid"
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- Evaluating the impact of storage capacity constraints on vehicular delay-tolerant networksPublication . Soares, V.N.G.J.; Farahmand, Farid; Rodrigues, JoelVehicular Delay-Tolerant Network (VDTN) was proposed as a particular application of a mobile Delay-Tolerant Network (DTN), where vehicles act as the communication infrastructure for the network, relaying messages between the network nodes. In this paper, we consider the use of a VDTN to provide low-cost asynchronous communication between sparse populations spread over a remote vast region. We analyze the influence of the VDTN network node’s storage capacity (buffer size), on the efficiency of four DTN routing protocols, in terms of message delivery probability. Our scenarios show that the routing protocols message replication strategies react differently to the increase of buffer size in specific network nodes. Epidemic and MaxProp protocols benefit from the increase of the storage capacity on all network nodes. Spray and Wait protocol only takes advantage on the increase of the vehicle’s buffer capacity. We expect that this paper will provide a deep understanding of the implications of storage constraints over the performance of a VDTN, leading to insights for future routing algorithm and buffer management theoretic studies and protocol design.
- Exploiting node localization for performance improvement of vehicular delay-tolerant networksPublication . Soares, V.N.G.J.; Rodrigues, Joel; Farahmand, Farid; Denko, Mieso K.Vehicular Delay-Tolerant Networks (VDTNs) are characterized by high node mobility, intermittent connectivity, and short contact durations. Such factors cause incomplete transmissions and the waste of link capacity. To address these issues, this paper explores the use of node localization in VDTNs. The exchange of signaling information related to nodes’ real-time location, current trajectory, velocity, and transmit range allows a Contact Prediction Algorithm to estimate contact durations. This information can be used in conjunction with additional signaling information (e.g. link data rate), to determine the maximum number of bytes that can be transmitted during contact opportunities. A Contact Duration Scheduling Policy can use this information to prevent incomplete transmissions, while increasing the number of successfully relayed bundles and improving data link utilization. Through a simulation study, we investigate the benefits of introducing the concept of node localization, and evaluate the performance of the proposed Contact Prediction Algorithm and Contact Duration Scheduling Policy. We demonstrate the gains introduced by this approach in comparison with an environment where VDTN nodes have no access to localization information.
- Impact analysis of the shortest path movement model on routing strategies for VDTNs in a rural regionPublication . Soares, V.N.G.J.; Rodrigues, Joel; Farahmand, FaridVehicular Delay-Tolerant Network (VDTN) appears as a particular application of the Delay-Tolerant Network (DTN) concept to transit networks. In this paper we analyze the use of a VDTN to provide asynchronous Internet access on a rural remote region scenario. Through simulation we evaluate the impact of a shortest path based movement model on the performance of four DTN routing protocols in respect to message delivery probability and message average delay.
- Impact of vehicle movement models on VDTN routing strategies for rural connectivityPublication . Soares, V.N.G.J.; Farahmand, Farid; Rodrigues, JoelVehicular delay-tolerant networks (VDTNs) appear as an alternative to provide low cost asynchronous internet access on developing countries or isolated regions, enabling non-real time services, such as e-mail, web access, telemedicine, environmental monitoring and other data collection applications. VDTNs are based on the delay-tolerant network (DTN) concept applied to vehicular networks, where vehicles mobility is used for connectivity. This paper considers a rural connectivity scenario and investigates how different mobility patterns and vehicle densities influence the performance of DTN routing protocols applied to VDTN networks. Moreover, routing protocols parameters are also changed in the present study. We analyse their effect on the performance of VDTNs through the bundle delivery ratio and the bundle average delay. We expect that this contribution will provide a deep understanding about implications of movement models on the performance of VDTNs applied to rural scenarios, leading to insights for future routing algorithm theoretic study and protocol design.
- Improving vehicular delay-tolerant network performance with relay nodesPublication . Soares, V.N.G.J.; Farahmand, Farid; Rodrigues, JoelVehicular Delay-Tolerant Networking (VDTN) is an extension of the Delay-Tolerant Network (DTN) architecture concept to transit networks. VDTN architecture handles non-real time applications, exploiting vehicles to enable connectivity under unreliable scenarios with unstable links and where an end-to-end path may not exist. Intuitively, the use of stationary store-and-forward devices (relay nodes) located at crossroads where vehicles meet them and should improve the message delivery probability. In this paper, we analyze the influence of the number of relay nodes, in urban scenarios with different numbers of vehicles. It was shown that relay nodes significantly improve the message delivery probability on studied DTN routing protocols.
- Inter-domain traffic routing in vehicular delay tolerant networksPublication . Farahmand, Farid; Patel, Ankitkumar N.; Soares, V.N.G.J.; Jue, Jason P.; Rodrigues, JoelIn this paper, we consider the problem of dynamic inter-domain traffic routing between a VDTN and a non-DTN (e.g., Internet). The inter-domain traffic can be classified as inbound and outbound traffic. Our main contribution in this work is the intro- duction of several fault-tolerant routing algorithms for inbound and outbound traffic. Using simulations, we compare the performance of the proposed algorithms in terms of required resources, packet delivery time, and blocking probability.
- A layered architecture for vehicular delay-tolerant networksPublication . Soares, V.N.G.J.; Farahmand, Farid; Rodrigues, JoelVehicular Delay-Tolerant Network (VDTN) is a new network architecture based on the concept of Delay Tolerant Networks (DTN). It aims to be an architecture that handles non-real time applications at low cost, under unreliable conditions, enabling connectivity in diverse scenarios, using vehicles to carry data between terminal nodes. For example, it can be applied in rural and remote areas, or in emergency scenarios. This paper proposes a layered architecture for VDTNs, using out-of-band signaling, based on the separation of the control plane and data plane. It presents the layers interactions and the envisioned protocols required at each layer. The paper provides a deep understanding of the characteristics of VDTN and reveal some design issues in its modeling, leading to insights for future theoretic study and protocol design.
- Método de transmissão de dados em redes veiculares com ligações intermitentesPublication . Rodrigues, Joel; Soares, V.N.G.J.; Farahmand, FaridA presente invenção diz respeito a uma nova arquitectura de comunicação de dados para redes veiculares, chamada rede veicular com ligações intermitentes, e ao respectivo método de transmissão de dados. Esta arquitectura introduz uma abordagem diferenciada à comunicação de dados em redes veiculares, baseada na combinação das seguintes técnicas: introdução de uma camada de ''''agregação'''' sobre a camada de ''ligação de dados'' segundo o modelo de referência OSI da ISO; paradigma de ''armazenamento, transporte e envio de agregados''; e separação do plano de controlo e plano de dados, utilizando sinalização fora-de-banda. O método de transmissão baseado nesta arquitectura, colmata as dificuldades da transmissão de dados em redes veiculares, e introduz a capacidade de agendamento de reservas de recursos. Desta forma, a presente invenção optimiza a utilização dos recursos restritos disponíveis nos nós de uma rede veicular e aumenta a probabilidade de entrega atempada de agregados, melhorando o desempenhos da rede.
- Performance analysis of scheduling and dropping policies in vehicular delay-tolerant networksPublication . Soares, V.N.G.J.; Farahmand, Farid; Rodrigues, JoelVehicular Delay-Tolerant Networking (VDTN) was proposed as a new variant of a delay/disruptive-tolerant network, designed for vehicular networks. These networks are subject to several limitations including short contact durations, connectivity disruptions, network partitions, intermittent connectivity, and long delays. To address these connectivity issues, an asynchronous, store-carry-and-forward paradigm is combined with opportunistic bundle replication, to achieve multi-hop data delivery. Since VDTN networks are resource-constrained, for example in terms of communication bandwidth and storage capacity, a key challenge is to provide scheduling and dropping policies that can improve the overall performance of the network. This paper investigates the efficiency and tradeoffs of several scheduling and dropping policies enforced in a Spray and Wait routing scheme. It has been observed that these policies should give preferential treatment to less replicated bundles for a better network performance in terms of delivery ratio and average delivery delay.
- Scheduling and drop policies for traffic differentiation on vehicular delay-tolerant networksPublication . Soares, V.N.G.J.; Farahmand, Farid; Rodrigues, JoelVehicular Delay-Tolerant Networks (VDTNs) are a promising technology for vehicular communications, creating application scenarios that enable non-real time services with diverse performance requirements. Because of scarce network resources (e.g. bandwidth and storage capacity) and node’s short contact durations, the underlying VDTN network infrastructure must be capable of prioritizing traffic. This paper investigates several scheduling and drop policies, which can be used to implement traffic differentiation. Priority Greedy, Round Robin, and Time Threshold scheduling polices are proposed. In terms of drop policy, the message with the lowest priority and the lowest remaining time-to-live is discarded first. We evaluate their efficiency and tradeoffs, through simulation. The results presented in this paper can be used as a starting point for further studies in this research field, and give helpful guidelines for future VDTN protocol design.