A Performance Analysis of Point-to-Point Routing along a Directed Acyclic Graph in Low Power and Lossy Networks

The ROLL working group at IETF is currently designing 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'sdestination. 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.