Search results for "Computer network"
showing 10 items of 1634 documents
Adaptive Collision Avoidance through Implicit Acknowledgments in WSNs
2008
The large number of nodes, typical of many sensor network deployments, and the well-known hidden terminal problem make collision avoidance an essential goal for the actual employment of WSN technology. Collision avoidance is traditionally dealt with at the MAC Layer and plenty of different solutions have been proposed, which however have encountered limited diffusion because of their incompatibility with commonly available devices.In this paper we propose an approach to collision avoidance which is designed to work over a standard MAC Layer, namely the IEEE 802.15.4 MAC, and is based on application-controlled delays of packet transmission times. The proposed scheme is simple, decentralized …
Cooperative RTS/CTS MAC with relay selection in distributed wireless networks
2009
This paper proposes a cooperative multiple access protocol based on the Distributed Coordination Function (DCF) Request-To-Send/Clear-To-Send (RTS/CTS) scheme for distributed wireless networks. It answers three key questions concerning cooperation from the network perspective, namely when to cooperate, whom to cooperate with and how to protect cooperative transmissions. According to our protocol, the cooperation is initiated only if the direct transmission fails. An optimal relay node is selected in a distributed manner according to instantaneous relay channel conditions without prior information or extra signaling among relay candidates in the network. An additional three-way handshake is …
Revisit of RTS/CTS Exchange in High-Speed IEEE 802.11 Networks
2005
IEEE 802.11 medium access control (MAC), called distributed coordination function (DCF), provides two different access modes, namely, 2-way (basic access) and 4-way (RTS/CTS) handshaking. The 4-way handshaking has been introduced in order to combat the hidden terminal phenomenon. It has been also proved that such a mechanism can be beneficial even in the absence of hidden terminals, because of the collision time reduction. We analyze the effectiveness of the RTS/CTS access mode, in current 802.11b and 802.11a networks. Since the rates employed for control frame transmissions can be much lower than the rate employed for data frames, the assumption on the basis of the 4-way handshaking introd…
High-Speed Machines: Typologies, Standards, and Operation under PWM Supply
2018
This paper presents an overview of the most recent state of the art in the field of high-speed electric machines fed through high-frequency converters. This type of systems is rapidly wide spreading in aeronautical and automotive applications, as well as microturbines. Each typology has its own advantages and downsides, which are analytically presented in this paper. Some types of high-speed electric machines require high-frequency voltage supply, highly stressing the dielectric materials of the winding insulation system. For this reason, in high-speed electric drives, premature failure may occur and a reduction of the total system reliability has been observed in the past years. Such issue…
Mechanisms of common ground in case-based web discussions in teacher education
2002
Previous studies suggest that before participants in web-based conferencing can reach deeper level interaction and learning, they have to gain an adequate level of common ground in terms of shared mutual understanding, knowledge, beliefs, assumptions, and presuppositions (Clark & Schaefer, 1989; Dillenbourg, 1999). In this paper, the purpose is to explore how participants establish and maintain common ground in order to reach deeper level interaction in case-based web discussions. The subjects in this study consisted of 68 preservice teachers and 7 mentors from 3 universities, who participated in a web-based conferencing course for 8 weeks. The written discussion data were analyzed by means…
Digital Cultural Heritage
2018
Most contemporary thinkers agree that we are going through a time of historical change, building adifferent concept and model of social interrelation. Our ways of life and work have changed, as havethe ways in which we communicate and relate to each other.
Las galeras mercantiles venecianas y el puerto de Valencia (1391-1534)
2020
This article studies the functioning of Venetian galere da mercato along one of the coastlines where they operated, that of Valencia. The system was known to have seven routes during the XIVth to the XVIth centuries and was used to collect goods at the point of arrival. The first galleys which carne to the port of Valencia (from Flanders) were in 1391, but the most active period was 1450-1534, from Aigues Mortes and Barbary. Analysis of fiscal and notarial records shows that the fleet system operated with the import of textiles, metal and spices and the export of wool, slaves and cloth, though the basic function of the market was the exchange of billion for spices. The market benefited fro…
H2S: A Secure and Efficient Data Aggregative Retrieval Scheme in Unattended Wireless Sensor Networks
2009
In unattended wireless sensor networks, data are stored locally and retrieved on demand. To efficiently transmit the collector’s retrieval results, data are aggregated along being forwarded. The data confidentiality and integrity should be protected at the intermediate nodes. End-to-end encryption or hop-by-hop encryption based schemes are not efficient. Straightforward homomorphic encryption based scheme is not compromise resilient. To achieve all the desires, we propose a scheme - H2S by making use of both homomorphic secret sharing and homomorphic encryption. The security and efficiency of our scheme are justified by extensive analysis.
A distributed data storage and retrieval scheme in unattended WSNs using Homomorphic Encryption and secret sharing
2009
Many data storage schemes have been proposed in the past for keeping dependable data storage, but they are not designed for Unattended Wireless Sensor Networks (UWSNs). When applying these schemes to UWSNs, most of them have limitations such as high storage requirement, transmission cost, and not resilient to a large number of node compromises. To address the problem of data storage, transmission cost, and resilience of node compromise in UWSNs, we propose a novel Homomorphic Encryption and Homomorphic Secret Sharing based scheme (HEHSS) to accomplish the goals of confidentiality, resilience to node compromises, reliability, and efficiency of storage and transmission. Our scheme exploits th…