Routing in Wi-SUN networks is adaptive — it evolves continuously as topology and link conditions change. This topic explains how RPL maintains and optimizes routes over time and how connectivity is sustained through the Border Router.

Route formation

When a network starts, the Border Router advertises routing information using RPL control messages. Nodes that receive these messages compute their rank and select one or more parent nodes based on link quality and routing cost. These parent-child relationships form the backbone of the mesh and establish the DODAG that defines traffic paths.

For an overview of how RPL builds and maintains this structure, see RPL protocol.

Path evaluation and optimization

Each node continuously evaluates its available parents and may switch to a better one when conditions improve. Routing decisions are influenced by both network constraints and link metrics:

  • Expected Transmission Count (ETX) — the estimated number of attempts needed to deliver a packet.

  • Signal-to-noise ratio (SNR) — a measure of link quality and stability.

  • Hop count and latency — indicators of distance and responsiveness to the Border Router.

  • Hop limit — an IPv6 parameter that prevents infinite routing loops.

RPL combines these metrics to balance reliability and efficiency rather than prioritizing shortest-path routing. By dynamically adjusting to link conditions, the mesh maintains optimal performance and self-corrects as the environment changes.

Route maintenance and communication

As devices join, move, or disconnect, the topology of the mesh evolves. RPL automatically detects these changes and updates routing tables accordingly. During these transitions, some nodes may temporarily lose upstream connectivity until new paths are established.

Wi-SUN’s self-healing behavior ensures continued operation even under variable conditions:

  • Nodes can reselect new parents if link quality degrades or a neighbor goes offline.

  • Control messages propagate changes through the DODAG, stabilizing routes without user intervention.

  • Multiple parent options provide redundancy and minimize disruption.

Peer-to-peer communication within the mesh is also supported when routes exist between devices. However, traffic typically follows the DODAG hierarchy — packets often travel upward toward the Border Router before being sent back down unless optimized paths exist between branches. This design favors consistency and reliability over minimal hop count.

Routing relies on IPv6 control mechanisms such as multicast and the Neighbor Discovery Protocol (NDP) to maintain neighbor awareness and distribute routing information. For more details, see Device discovery and reachability.