Catálogo de publicaciones - libros

Remote interaction with immersive 3D environments with acceptable level of quality of experience has become a challenging and interesting research topic. Due to the high data volume required to provide a rich experience to the user, robust and efficient wireless transport protocols have yet to be developed. On the other hand, cellular network technology has been widely deployed and is growing fast. The provision of remote interactive 3D environments over wireless cellular networks has several interesting applications, and it imposes some unsolved issues. Node mobility creates unstable bandwidth, which is a problem when providing smooth interaction to users. Although PDAs and cell phones are low resource devices, which makes it prohibitive to load and render entire virtual environments, they can still render images with relative ease. Based on this idea, this paper proposes a streaming system which relies on an image-based rendering approach, and is composed of several modules: a packetization scheme for images, an image-based rendering approach based on view morphing and its corresponding RTP payload format, and finally a bandwidth feedback mechanism and rate control. This paper illustrates some of the problems faced in this area, and provides a first step towards their solutions. We discuss our algorithms and present a set of simulation experiments to evaluate the performance of the proposed schemes.

This paper proposes a new signaling paradigm and a new signaling protocol called the Generic Context Sharing Protocol (GCSP) for the construction of a global control plane over present and future communication networks. After identifying the special nature of the control plane software involved in the setup of a conversational service instance it examines the various mechanisms for information sharing which leads to our new proposal. We show that this new data-based protocol is better suited to control plane requirements than the present day’s command-oriented signaling mechanisms. We indicate the basic principles of the protocol and we give a brief description of the generic context. We show the place of this proposal in the present day research efforts and we mention a practical implementation case.

As they are used to create open communities, Mobile Ad hoc NETworks (MANETs) are not favourable environments to establish trust, which is necessary to provide security. Multipath routing mechanisms within infrastructureless networks environment seems appropriate and useful to enhance security protection. In fact, the level of trust can be increased so as many of potential security attacks are detected, revealed and stopped. Nevertheless an excessive control overhead is always generated. In this paper, we propose a global framework that integrates a set of concepts and mechanisms aiming at enhancing security in highly dynamic decentralized ad hoc networks. Our solution focuses on authentication, routing securing, trust management with reliable estimation of trust. A large panoply of attacks are prevented using our various mechanisms.

The Brazilian government intends to use the Digital TV technology as a vehicle of digital inclusion on underserved communities. The wireless ad hoc network is a low-cost, scalable and easy solution to implement the return channel. This work analyzes the performance of an ad hoc return channel using the wireless IEEE 802.11 technology in different Brazilian geographical scenarios. The results show that a high connectivity is achieved when more than 20% of the nodes are turned on, regardless of the position of the gateway. The influence of the number of hops and the number of transmitting nodes is also analyzed. A minimum throughput of 2 Mbps can be reached for increasing number of hops in the forwarding chain for a one-node transmission. Besides, when the number of transmitting nodes increases, the aggregated throughput can achieve 3.5 Mbps. The results show that the ad hoc network is a promising solution for the return channel of the interactive Digital TV.

With the rapid development of short-range wireless technology new venues to apply it in more sophisticated, complex, and dynamic environments have been opened. Nevertheless, the applicability of such technology in non-traditional settings like face-to-face encounters and disaster relief environments, remains unclear. This article describes a research effort aimed to narrow that gap by means of using two non-traditional settings as case studies; face-to-face encounters among unacquainted people and first responders in urban disaster relief environments. Among the results obtained are: a) interactions among unacquainted people may be promoted, though the level of interaction becomes easily constrained due to the current state of RF technology and the design of the experiments, and b) it is feasible to obtain a reliable communication platform for first responders operating in disaster relief missions. These results supports the idea that short-range wireless technology may play both a facilitator and a promoter role in face-to-face contexts, and at least a facilitator role in the case of users co-located in highly dynamic contexts.

This paper presents a time-based admission control mechanism (TAC) for IEEE 802.11 ad hoc networks. The proposed mechanism was adapted to the QoS AODV routing protocol, which takes the quality of service requirements of the data flow into account in the route discovery process. TAC-AODV estimates the idle time of the physical medium based on the frames listened. The incoming traffic is admitted according to the offered load as well as the intra-flow interference, calculated based on the number of hops in the forwarding chain. TAC-AODV is compared to AAC-AODV, another admission control mechanism found in the literature, and the simulation results show that TAC-AODV is in average 12.5% better in terms of the packet delivery rate.

Wireless Technologies have allowed a fast growing of the Internet service in both public and private environments where wireless networks mostly consist of nodes interconnected with a fixed infrastructure; nevertheless, they do not offer a good performance in all the wide variety of services that are required for applications. Although the IEEE 802.11 MAC protocol is the standard for wireless LANs, this protocol shows a very poor performance and reliability compared with the multicast traffic transmitted in wired networks, this represents a significant challenge for existing 802.11 networks because it requires transmission over multiple unreliable channels to heterogeneous receivers with different connection bit rates and very limited feedback information to the sender. In this paper, we discuss the drawbacks of several protocols proposed in the literature that offer reliable multicast service. In addition, this work evaluates the performance of the wireless networks under multicast traffic and presents a proposal for actual IEEE802.11 networks to improve their efficiency. It uses a reliability control based on a polling service along with controlled retransmissions; this allows servicing nodes applications with a high efficiency without deteriorating fairness in the service. We present details of a prototype implementation and results that suggest that our protocol performs better than other proposed in terms of reliability as well as data throughput in our measurement scenarios.