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One of the widely used communication patterns in WSN is routing convergecast traffic to one or more sinks. In order to collect data at a sink, most existing systems use a tree rooted at the sink as underlying structure. We consider in this paper the Shortest Path routing Tree problem in WSN under different metrics; we show that the basic approach commonly used in the literature is unsuitable for the many-to-one WSN when considering some metrics. Indeed, existing SPT approaches aim to construct a tree rooted at the sink such that the cost of the path from any node to the sink is minimal, while the cost of a given path is computed as summation of the costs of links that compose this path. However, in many-to-one WSN, links which are close to the sink are more solicited to route packets towards the sink and, hence, they are more critical than other links. Therefore, links in the tree should not have the same weight. We propose in this paper a new weighted path cost function, and we show that our cost function is more suitable for WSN. Based on this cost function, we propose a new efficient shortest path tree construction which does not introduce any new communication overhead compared to basic SPT schemes. We consider, then, the particular case of energy-aware routing in WSN when we apply our new solution in order to construct more suitable energyaware SPT. We conduct extensive simulations which show that our approach allows to enhance the network lifetime up to 20% compared to the basic one.

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This paper proposes a congestion control solution for CoAP/ RPL/6LoWPAN networks. CoAP/RPL/6LoWPAN has been considered as one of the most appropriate protocol stack for industrial applications of the Internet of Things (IoT). Since IoT nodes may have constrained resources, mechanisms used to control congestion must operate effectively with minimal consumption. In this paper, a method for congestion control in an IoT environment governed by the CoAP/RPL/6LoWPAN protocol stack is proposed. Our solution is based on the concept of bird flocking to guide packets in order to avoid congestion. Simulation shows that our proposal guarantees better results compared to congestion control mechanisms of the protocol stack in terms of data latency, packet loss ratio and packet delivery ratio.