M.D. de Amorim

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.

Securing wireless sensor networks against aggregator compromises

A common approach to overcome the limited nature of sensor networks is to aggregate data at intermediate nodes. A challenging issue in this context is to guarantee end-to-end security mainly because sensor networks are extremely vulnerable to node compromises. We propose three schemes to secure data aggregation that rely on multipath routing. The first guarantees data confidentiality through secret sharing, while the second and third provide data availability through information dispersal. Based on qualitative analysis and implementation, we show that by applying these schemes, a sensor network can achieve data confidentiality, authenticity, and protection against denial of service attacks even in the presence of multiple compromised nodes.

Dynamic Service Contract Enforcement in Service-Oriented Networks

In recent years, service-oriented architectures (SOA) have emerged as the main solution for the integration of legacy systems with new technologies in the enterprise world. A service is usually governed by a client service contract (CSC) that specifies, among other requirements, the rate at which a service should be accessed, and limits it to no more than a number of service requests during an observation period. Several approaches, using both static and dynamic credit-based strategies, have been developed to enforce the rate specified in the CSC. Existing approaches have problems related to starvation, approximations used in calculations, and rapid credit consumption under certain conditions. In this paper, we propose and validate DoWSS, a doubly weighted algorithm for service traffic shaping. We show via simulation that DoWSS possesses several advantages: It eliminates the approximation issues, prevents starvation, and contains the rapid credit consumption issue in existing credit-based approaches.

Application-aware multicast

Measuring the quality of multicast multi-layered applications based only on the amount of data that arrives at the receivers is insufficient in many circumstances. This paper proposes a three-metric approach that improves the global quality/fairness of the multicast sessions. We define a simple function that takes into account the density of satisfied users, the amount of allocated bandwidth in the multicast tree, and the degradation at the receivers. We analyze the proposed multicriteria algorithm in an environment with other competing flows and show the improvement of the global quality of multicast multi-layered applications.

Implicit merging of overlapping spontaneous networks [mobile ad hoc networks]

Due to mobility, spontaneous networks composed of nodes following similar group mobility patterns are likely to overlap. Previous solutions invariably considered overlapping as a permanent state where the networks combine to form a new network. In this paper, we propose a more realistic model where merging is either permanent or transient. Our contributions are twofold. First, we introduce a methodology to identify transient merging and detect implicit permanent merging. Second, we propose an efficient routing protocol between merging networks while in the transient state. Our approach is completely distributed and incurs low routing control overhead. We also investigate a solution to prevent respective intra-network communications from interfering.

Design and Evaluation of an Agenda-Based Location Service

An interesting approach for the location service problem in wireless mesh networks is the one that relies on location agendas to model node displacements on an absolute time basis. To the best of our knowledge, the literature still lacks the design and evaluation of such an approach. In this paper, we introduce and analyze an agenda-based location service that reduces the overhead due to location updates. We evaluate the performance of our scheme with real mobility traces and observe that mobile nodes spend in average 80% of their time at a maximum distance of one hop from the expected locator. Furthermore, 81% of the location update messages are constrained within this radius. This drastically reduces the propagation areas when compared for instance with DHT-based approaches.

An Absration Layer for Neighborhood Discovery and Cross-Layer Metrics

Topology-awareness is an important feature of communication algorithms and protocols for wireless multi-hop networks. In its basic form, topology-awareness requires nodes to know their immediate neighbors and, if possible, the quality of the links between them. In general, neighborhood discovery is done by routing protocols; the problem with such an approach is that fundamental changes in node characteristics require revisiting the routing protocol, especially if this latter relies on cross-layer metrics. In this paper, we propose an abstraction layer that performs neighborhood discovery and link quality assessment. In this way, neighborhood discovery is decoupled from the upper layers. Our abstraction layer stands as an active building block for the implementation of routing protocols or any other IEEE 802.11 communication algorithm for wireless multi-hop networks. It provides an updated list of neighbors, along with several statistics about link quality that can be used, for instance, to compute cross-layer metrics.

EPEW: An extended prototyping environment for wireless mesh networks

This paper introduces EPEW, an environment for rapid prototyping of communication protocols over IEEE 802.11 mesh networks. EPEW provides a software environment that makes prototyping as quick, easy, and effortless as possible, which allows researchers to conduct both functional assessment and performance evaluation as an integral part of the protocol design process. Since EPEW runs on real IEEE 802.11 wireless mesh routers and clients, prototypes can be evaluated and adjusted under realistic conditions. EPEW facilitates prototype development by providing: (i) a set of building blocks that implement common functions needed by a wide range of protocols for wireless mesh networks, and (ii) an API that allows protocol designers to access EPEW primitives.

Socially-motivated Wireless Neighborhood Communities

In this paper, we promote the use of online communities as a means to provide incentives for people to collaborate in building wireless community networks. To achieve this goal, we define a novel type of online community spanning a specific physical area (i.e., a neighborhood) called wireless neighborhood community (WNC). On the one hand, in addition to the standard activities of an online neighborhood community (e.g. i-neighbors), a WNCs members cooperate to build a network and share their resources at different layers. On the other hand, in addition to standard wireless community networks being deployed today in big cities, a WNC incorporates the social layer in its design. It is a hybrid (both virtual and physical) community whose activities are linked to the operation and management of the underlying network. If designed appropriately, this cross-layer community will provide incentive to users to participate and share their resources, build trust, and increase the social capital in the city. We provide insights for exploiting this special characteristic of the WNC towards these objectives, introducing the notion of a cross-layer incentive mechanism and the corresponding network-aware social software.

An improved MPEG behavioral analysis with autonomous parameter-extracting algorithm for strict video applications

Through a detailed analysis of theoretical and real MPEG-compressed video streams, this paper addresses the task of extracting deterministic parameters from such sources in order to provide deterministic service guarantees. We propose and analyze the single-input single-output (SISO) algorithm with quality adjustment to compute the coherent parameters for the XGOP-B deterministic traffic model. Contrary to other proposals, the SISO algorithm leads to a single set of parameters for each input traffic and does not ask for external decisions to perform this stage. Moreover, the accuracy/complexity can be adjusted by a special variable. Our results show that the proposed approach leads to improved accuracy and that the complexity can be decreased by three orders of magnitude.