Igor M. Moraes

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.

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.

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.

Implementing the Expected Transmission Time Metric for OLSR Wireless Mesh Networks

This paper presents the design of a plug-in for the optimized link state routing (OLSR) protocol with the expected transmission time (ETT) metric and experiments in an indoor testbed. The ETT metric is implemented as a plug-in, keeping portability and facilitating its deployment on operational networks. Our design identifies important implementation issues. Additionally, we run experiments in an indoor testbed to verify the performance of our ETT plug-in. Our results show that the ETT metric has the lowest packet loss rate and the lowest round trip time among the analyzed metrics, because it reproduces link quality conditions and also takes into account physical transmission rates.

The ad hoc return channel: a low-cost solution for Brazilian interactive digital TV

The upcoming terrestrial digital television technology brings a new class of services to traditional TV sets. A set-top box may, for example, access the Internet and send email. The interactive return channel makes these new services possible. This channel allows TV viewers to interact by sending data back to the TV broadcaster. In this article we analyze the viability of a wireless ad hoc network to implement the return channel. For this purpose, an ad hoc network is a low-cost and flexible solution. We evaluate the performance of an ad hoc return channel using the IEEE 802.11 wireless technology for different Brazilian geographical scenarios. The results show that ad hoc networking is a promising solution for the return channel of Brazilian interactive digital TV

Towards Stateless Single-Packet IP Traceback

The current Internet architecture allows malicious nodes to disguise their origin during denial-of-service attacks with IP spoofing. A well-known solution to identify these nodes is IP traceback. In this paper, we introduce and analyze a lightweight single-packet IP traceback system that does not store any data in the network core. The proposed system relies on a novel data structure called Generalized Bloom Filter, which is tamper resistant. In addition, an efficient improved path reconstruction procedure is introduced and evaluated. Analytical and simulation results are presented to show the effectiveness of the proposed scheme. The simulations are performed in an Internet-based scenario and the results show that the proposed system locates the real attack path with high accuracy.

On the impact of user mobility on peer-to-peer video streaming

Wireless mesh networks are emerging as a promising solution for ubiquitous Internet access with mobility support. In such networks, user mobility may lead to Internet gateway changes and consequently, impact the performance of continuous media applications. In this article, we investigate the impact of user mobility on the performance of peer-to-peer video applications over wireless mesh networks. Peer-to-peer video streaming applications rely on the collaborative behavior of peers to assist the source in delivering multimedia content, reduce costs, and increase the scalability of video distribution. We identify practical issues related to mobility for P2P video streaming implementation in WMNs, such as addressing and forwarding strategies. Furthermore, we evaluate the performance of different P2P streaming applications as the user walks in our WMN testbed. Results indicate mobile users benefit from the frequent shortlived connections established in modern P2P video sessions.

Modelling the Data Aggregator Positioning Problem in Smart Grids

Smart meters are responsible for keeping track of user energy consumption in a smart grid infrastructure. This data is periodically sent to one or more data aggregation points (DAPs), typically via wireless communication. Efficiently choosing the best positions for installing DAPs is an NP-Complete problem and therefore a difficult task, specially in big cities that may contain thousands of smart meters in a single neighborhood. Nevertheless, network planning has a major impact on network performance. This work proposes a reduction of the DAP positioning problem to a problem in the optimization area known as the Set Covering and a heuristic to solve it. This reduction considers a pre-processed subset of reliable links estimated based on the neighborhood characteristics, devices communication technology, antenna heights and transmission rate. The obtained solution corresponds to the least number of DAPs, and its positions, necessary to cover an entire neighborhood. Our heuristic divides the problem in smaller independent sets that are solved separately and united afterwards. A post-optimization method is also applied in order to improve the heuristics solution. Heuristic and linear programming techniques are compared and results show that our heuristic is capable of obtaining solutions 0.05% close to the optimal while reducing both the execution time and the memory consumption by 2.27 and 8.14 times, respectively. Additionally, our heuristic was able to obtain results for large instances where the optimal solution failed due to insufficient memory.

A joint custody-based forwarding policy for delay-tolerant networks

In this paper, we propose a custody-based approach to improve network performance in DTNs. Therefore, we introduce a mechanism that comprises a joint-custody scheme, named Limited Joint Custody (LJC) and a forwarding policy, named Forward Custody First (FCF). LJC uses a limited replication mechanism to control the number of custodians per bundle in the network and FCF prioritizes bundles in custody. We evaluate, through simulations, the performance of our proposed mechanisms under two different trace-based scenarios. We also compare LJC and FCF with existing solutions in the literature. Main results show a significant improvement in delivery delay and rate in both scenarios, with no additional overhead. FCF-LJC presents a delivery rate of 98% at the same time that decreases by 24% the delivery delay.

A Lifetime-Based Peer Selection Mechanism for Peer-to-Peer Video-on-Demand Systems

In this paper, we propose a peer selection mechanism for peer-to-peer video-on-demand (P2P-VoD) systems. The goal of our mechanism is to increase the availability of chunks between a peer and its partners. For this purpose, the process of selecting partners is based on the lifetime of peers, which is time since the beginning of the video playback. Thus, a peer selects as partners other peers with close lifetimes to increase the probability of finding chunks of interest in these selected partners. Results show that the proposed mechanism is efficient for different interactivity patterns. With the proposed mechanism, more than 97% of the video chunks required by a peer are available on its selected partners. This result is achieved even considering that only 10% of the video chunks can be cached by partners. In opposition, the conventional random selection mechanism requires much more disk space, which corresponds to a cache size of at least 70% of chunks, to provide the same level of availability