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In the past few years, the number of wireless devices connected to the Internet has increased to a number that could reach billions in the next few years. While cloud computing is being seen as the solution to process this data, security challenges could not be addressed solely with this technology. Security problems will continue to increase with such a model, especially for private and sensitive data such as data personal and medical data collected with more and more sophisticated connected devices (forming the IoT). Thus the need for a fully decentralized peer to peer and secure technology to overcome these problems. The blockchain Technology is a promising approach giving the properties it brings to the field. This paper illustrates an architecture based on blockchain technology, and a protocol for data access, using smart contracts and a publisher-subscriber mechanism.

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In the past few years, the number of wireless devices connected to the Internet has increased to a number that could reach billions in the next few years. While cloud computing is being seen as the solution to process this data, security challenges could not be addressed solely with this technology. Security problems will continue to increase with such a model, especially for private and sensitive data such as personal data and medical data collected with more and more smarter connected devices constituting the so called Internet of Things. As a consequence, there is an urgent need for a fully decentralized peer-to-peer and secure technology solution to overcome these problems. The blockchain technology is a promising just-in-time solution that brings the required properties to the field. However, there are still challenges to address before using it in the context of IoT. This paper discusses these challenges and proposes a secure IoT architecture for medical data based on blockchain technology. The solution introduces a protocol for data access, smart contracts and a publisher-subscriber mechanism for notification. A simple analytical model is also presented to highlight the performance of the system. An implementation of the solution as a proof of concept is also presented. technologies that will drive IoT security towards a more decentralized model.Having this huge amount of data, being centralized and sometimes monitored by one single provider, may create many problems. The cloud as a computing/storing technology cannot only by itself protect the security and privacy of its users. Using a decentralized approach for IoT network security is eventually an interesting way to solve many of the challenges IoT technology is facing today. Adopting a peerto-peer model to handle billions of transactions between the billions of interconnected devices will decrease dramatically the costs of installation and maintenance of data centers and servers. It will also allow the distribution of storage and processing power on different devices and components of the network increasing the reliability of the system; e.g., the failure of one node will not cause the entire network to halt or collapse.However, in order to establish well-defined peer-to-peer communication protocols, a whole other set of challenges will need to be addressed, mainly security and privacy. Some level

Extensive research addressing IEEE 802.11e enhanced distributed channel access (EDCA) performance analysis, by means of analytical models, exist in the literature. Unfortunately, the currently proposed models, even though numerous, do not reach this accuracy due to the great number of simplifications that have been done. Particularly, none of these models considers the 802.11e contention free burst (CFB) mode which allows a given station to transmit a burst of frames without contention during a given transmission opportunity limit (TXOPLimit) time interval. Despite its influence on the global performance, TXOPLimit is ignored in almost all existing models. To fill in this gap, we develop in this paper a new and complete analytical model that (i) reflects the correct functioning of EDCA, (ii) includes all the 802.11e EDCA differentiation parameters, (iii) takes into account all the features of the protocol, and (iv) can be applied to all network conditions, going from nonsaturation to saturation conditions. Additionally, this model is developed in order to be used in admission control procedure, so it was designed to have a low complexity and an acceptable response time. The proposed model is validated by means of both calculations and extensive simulations.