Routing issues are very challenging for 6LoWPAN, given the low-power and lossy radio-links, the battery supplied nodes, the multi-hop mesh topologies, and the frequent topology changes due to mobility. Successful solutions should take into account the specific application requirements, along with IPv6 behavior and 6LoWPAN mechanisms . An effective solution was developed by the IETF “Routing Over Low power and Lossy (ROLL) networks” working group [ROLL WG]. It has proposed the leading IPv6 Routing Protocol for Lowpower and Lossy Networks (LLNs), RPL, based on a gradient-based approach [RPL], [RPLwhitepaper].
RPL can support a wide variety of different link layers, including ones that are constrained, potentially lossy, or typically utilized in conjunction with host or router devices with very limited resources, as in building/home automation, industrial environments, and urban applications. It is able to quickly build up network routes, to distribute routing knowledge among nodes, and to adapt the topology in a very efficient way.
In the most typical setting entailed by RPL, the nodes of the network are connected through multi-hop paths to a small set of root devices, which are usually responsible for data collection and coordination duties. For each of them, a Destination Oriented Directed Acyclic Graph (DODAG) is created by accounting for link costs, node attributes/status information, and an Objective Function, which maps the optimization requirements of the target scenario.
RPL can encompass different kinds of traffic and signaling information exchanged among nodes depends on the requirements of the considered data flows. In details, it supports: Multipoint-to-Point (MP2P), Point-to-Multipoint (P2MP), and Point-to-Point (P2P) traffic.
[RPL] T. Winter, P. Thubert, A. Brandt, J. Hui, R. Kelsey, P. Levis, K. Pister, R. Struik, J. P. Vasseur, and R. Alexander, RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks, RFC 6550, Internet Engineering Task Force RFC 6550, March 2012.
[RPLwhitepaper] J. Vasseur, N. Agarwal, J. Hui, Z. Shelby, P. Bertrand, and C. Chauvenet, “RPL: The IP routing protocol designed for low power and lossy networks,” Internet Protocol for Smart Object (IPSO) Alliance, White Paper, April 2011.