3.1.1. Constructing Topologies

LLNs, such as Radio Networks, do not typically have predefined topologies, for example, those imposed by point-to-point wires, so RPL has to discover links and then select peers sparingly.

In many cases, because Layer 2 ranges overlap only partially, RPL forms non-transitive / Non-Broadcast Multi-Access (NBMA) network topologies upon which it computes routes.

RPL routes are optimized for traffic to or from one or more roots that act as sinks for the topology. As a result, RPL organizes a topology as a Directed Acyclic Graph (DAG) that is partitioned into one or more Destination Oriented DAGs (DODAGs), one DODAG per sink. If the DAG has multiple roots, then it is expected that the roots are federated by a common backbone, such as a transit link.