Otto Carlos Muniz Bandeira Duarte

Routing Metrics and Protocols for Wireless Mesh Networks

WMNs are low-cost access networks built on cooperative routing over a backbone composed of stationary wireless routers. WMNs must deal with the highly unstable wireless medium. Therefore, the design of algorithms that consider link quality to choose the best routes are enabling routing metrics and protocols to evolve. In this work, we analyze the state of the art in WMN metrics and propose a taxonomy for WMN routing protocols. Performance measurements for a WMN, deployed using various routing metrics, are presented and corroborate our analysis.

Trust management in mobile ad hoc networks using a scalable maturity-based model

In this paper, we propose a human-based model which builds a trust relationship between nodes in an ad hoc network. The trust is based on previous individual experiences and on the recommendations of others. We present the Recommendation Exchange Protocol (REP) which allows nodes to exchange recommendations about their neighbors. Our proposal does not require disseminating the trust information over the entire network. Instead, nodes only need to keep and exchange trust information about nodes within the radio range. Without the need for a global trust knowledge, our proposal scales well for large networks while still reducing the number of exchanged messages and therefore the energy consumption. In addition, we mitigate the effect of colluding attacks composed of liars in the network. A key concept we introduce is the relationship maturity, which allows nodes to improve the efficiency of the proposed model for mobile scenarios. We show the correctness of our model in a single-hop network through simulations. We also extend the analysis to mobile multihop networks, showing the benefits of the maturity relationship concept. We evaluate the impact of malicious nodes that send false recommendations to degrade the efficiency of the trust model. At last, we analyze the performance of the REP protocol and show its scalability. We show that our implementation of REP can significantly reduce the number messages.

Hop by hop multicast routing protocol

IP Multicast is facing a slow take-off although it is a hotly debated topic since more than a decade. Many reasons are responsible for this status. Hence, the Internet is likely to be organized with both unicast and multicast enabled networks. Thus, it is of utmost importance to design protocols that allow the progressive deployment of the multicast service by supporting unicast clouds. This paper proposes HBH (Hop-By-Hop multicast routing protocol). HBH adopts the source-specific channel abstraction to simplify address allocation and implements data distribution using recursive unicast trees, which allow the transparent support of unicast-only routers. Additionally, HBH is original because its tree construction algorithm takes into account the unicast routing asymmetries. As most multicast routing protocols rely on the unicast infrastructure, these asymmetries impact the structure of the multicast trees. We show through simulation that HBH outperforms other multicast routing protocols in terms of the delay experienced by the receivers and the bandwidth consumption of the multicast trees.

Joint Adoption of QoS Schemes for MPEG Streams

Abstract.Indiscriminated packet discards strongly degrade the quality perceived by end users of MPEG video transmissions. This paper investigates different Quality of Service (QoS) schemes and the tradeoffs of jointly adopting such schemes to improve the delivery quality of an MPEG stream. From an analytical model, we evaluate the impact of frame losses on the quality of MPEG streams and on the waste of network resources. Our assessment considers issues such as the use of redundancy by applying a Forward Error Correction (FEC) scheme to tolerate losses, the changing of the compression factor in MPEG encoding, the unequal protection of MPEG frames in a Differentiated Services environment, and how to evaluate the impact of network losses onto application quality. Results provide predicted bounds on the quality to be expected by end users as well as guidelines on how to take the best advantage from the joint adoption of the investigated QoS schemes.

Virtual networks: isolation, performance, and trends

Currently, there is a strong effort of the research community in rethinking the Internet architecture to cope with its current limitations and support new requirements. Many researchers conclude that there is no one-size-fits-all solution for all of the user and network provider needs and thus advocate for a pluralist network architecture, which allows the coexistence of different protocol stacks running at the same time over the same physical substrate. In this paper, we investigate the advantages and limitations of the virtualization technologies for creating a pluralist environment for the Future Internet. We analyze two types of virtualization techniques, which provide multiple operating systems running on the same hardware, represented by Xen, or multiple network flows on the same switch, represented by OpenFlow. First, we define the functionalities needed by a Future Internet virtual network architecture and how Xen and OpenFlow provide them. We then analyze Xen and OpenFlow in terms of network programmability, processing, forwarding, control, and scalability. Finally, we carry out experiments with Xen and OpenFlow network prototypes, identifying the overhead incurred by each virtualization tool by comparing it with native Linux. Our experiments show that OpenFlow switch forwards packets as well as native Linux, achieving similar high forwarding rates. On the other hand, we observe that the high complexity involving Xen virtual machine packet forwarding limits the achievable packet rates. There is a clear trade-off between flexibility and performance, but we conclude that both Xen and OpenFlow are suitable platforms for network virtualization.

Improving the Data Transmission Throughput over the Home Electrical Wiring

Powerline communications (PLC) are receiving special attention since they use an already available and ubiquitous infrastructure. The main standard for PLC home networks is HomePlug. This work improves the throughput of HomePlug by modifying the medium access control sub-layer. The key idea is to define a fast collision avoidance mechanism where every station that wants to access the medium increments its contention window after sensing another ongoing transmission. The proposal reduces the number of collisions in the network improving the achievable throughput. We compared our mechanism to the original HomePlug standard through simulation and mathematical analysis. We verified that the improvement is independent from the packet size, the transmission rate and the number of nodes when the network is high loaded

Measuring the capacity of in-car to in-car vehicular networks

A particular class of vehicular networks is the one that includes off-the-shelf end-user equipment (e.g., laptops and PDAs) running from the interior of vehicles: in-car nodes. They are subject to limited communication conditions when compared with nodes specifically designed to this context. Existing works either consider antennas installed on top of the vehicle roof or nodes that operate in infrastructure mode. In this article, we investigate through real experiments the characteristics of links formed by in-car nodes running off-the-shelf wireless technologies such as IEEE 802.11(a/g) in ad hoc mode. We surprisingly observe that in-car nodes do show enough performance in terms of network capacity to be used in a number of applications, such as file transfer in peer-to-peer applications. Nonetheless, we identify some key performance issues and devise a number of configuration recommendations and future work directions.

Improving the accuracy of measurement-based geographic location of internet hosts

Location-aware applications take into account from where the users are accessing and thereby can offer novel functionalities in the Internet. This paper focuses on improving the accuracy of a geographic location service that relies on delay measurements to locate Internet hosts. Host locations are inferred by comparing delay patterns of geographically distributed landmarks, which are hosts with a known geographic location, with the delay pattern of the target host to be located. We deal with two problems that influence the accuracy of the resulting location estimation: (i) the placement of the landmarks and the probe machines that perform the delay measurements; and (ii) how to best measure the similarity between the delay patterns of the landmarks and the one observed for the target host. For the landmark placement problem, we propose a demographic approach to improve the representativeness of each landmark with respect to the hosts to be located. Given a limited number of landmarks, results show that a demographic placement provides closer landmarks and more accurate location estimations for most hosts. Concerning the placement of probe machines, we show that they have to be sparsely placed to avoid gathering redundant data. Furthermore, we define and evaluate three similarity models. Experiments show that other similarity models outperform the commonly adopted Euclidean distance, resulting then in a more accurate geographic location of Internet hosts.

A Survey on Wireless Ad Hoc Networks

A wireless ad hoc network is a collection of wireless nodes that can dynamically self-organize into an arbitrary and temporary topology to form a network without necessarily using any pre-existing infrastructure. These characteristics make ad hoc networks well suited for military activities, emergency operations, and disaster recoveries. Nevertheless, as electronic devices are getting smaller, cheaper, and more powerful, the mobile market is rapidly growing and, as a consequence, the need of seamlessly internetworking people and devices becomes mandatory. New wireless technologies enable easy deployment of commercial applications for ad hoc networks. The design of an ad hoc network has to take into account several interesting and difficult problems due to noisy, limited-range, and insecure wireless transmissions added to mobility and energy constraints. This paper presents an overview of issues related to medium access control (MAC), routing, and transport in wireless ad hoc networks and techniques proposed to improve the performance of protocols. Research activities and problems requiring further work are also presented. Finally, the paper presents a project concerning an ad hoc network to easily deploy Internet services on low-income habitations fostering digital inclusion.

OpenFlow and Xen-Based Virtual Network Migration

Migration is an important feature for network virtualization because it allows the reallocation of virtual resources over the physical resources. In this paper, we investigate the characteristics of different migration models, according to their virtualization platforms. We show the main advantages and limitations of using the migration mechanisms provided by Xen and OpenFlow platforms. We also propose a migration model for Xen, using data and control plane separation, which outperforms the Xen standard migration. We developed two prototypes, using Xen and OpenFlow, and we performed evaluation experiments to measure the impact of the network migration on traffic forwarding.