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International audienceThe ROLL working group at IETF is currently de- signing RPL, the Routing Protocol for Low power and lossy networks. RPL is based on organizing the nodes in a network in one or more directed acyclic graphs (DAGs) rooted at the popular/default destinations. The DAG structure naturally supports multipoint-to-point routing towards the DAG root and point-to-multipoint routing from the root towards the nodes. The point- to-point (P2P) routing mechanism specified in RPL requires a packet to travel upwards along the DAG until it is turned downwards by a node that knows the downward route along the DAG to the packet's destination. This up and down routing along the DAG may result in significantly suboptimal P2P routes. In this paper, we quantify the difference in terms of routing cost between DAG-based P2P routes and the shortest (or minimum cost) P2P routes available in a sample network topology and make the case for a better P2P routing solution in RPL

Abstract-Directed Acyclic Graphs (DAGs), rooted at popular/default destinations, have emerged as a preferred mechanism to provide IPv6 routing functionality in large scale low power and lossy networks, that include wireless sensor networks and those based on power line communication. A DAG maintains its acyclic nature by requiring that each DAG node must have a higher 'rank' than any of its DAG parents. While a node may decrease its DAG rank safely, increasing its DAG rank to add a new parent may result in a routing loop if the new parent is also a descendant in the DAG. In this paper, we first study via simulations the time required by the network to converge to a stable, loop-free state following a rank increase operation and the number of routing messages generated (the network 'churn') during this time. Then, we describe the precautionary measures that can be used to avoid routing loops and evaluate via simulations how these measures affect the time and churn involved in reaching a stable state following a rank increase operation.

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IEEE 802.15.4, a MAC/PHY protocol for low power and low data rate wireless networks, is emerging as the popular choice for various monitoring and control applications. Depending on the application, the traffic load on an IEEE 802.15.4 network may vary over a wide range. The performance of the protocol, measured in terms of the packet loss probability and the packet latency, depends upon the prevailing traffic load as well as the configuration of IEEE 802.15.4 MAC parameters.Static configuration of IEEE 802.15.4 MAC parameters, good for a particular traffic load range, may result in bad performance when the traffic load changes beyond that range. In this paper, we present a scheme that can be used by an IEEE 802.15.4 node to dynamically adjust its MAC configuration based on the observed loss rate and latency suffered by recent packets generated by the node. The performance benefits of the proposed scheme are illustrated via NS2 simulations.

In this article, the authors propose modifications to OSPF's interface state machine to reduce the time/processing requirements of the leader election process in a broadcast local-area network (LAN) environment. The proposed modifications are based on dynamic adjustment of wait time duration rather than using a static value. They compare the original and modified state machines both analytically as well as via testbed experiments.

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