Wi-SUN (Wireless Smart Ubiquitous Network) is a wireless communication standard for large-scale, outdoor, and industrial IoT deployments. It builds on open IEEE and IETF standards such as IEEE 802.15.4g/e for the physical and MAC layers, IPv6 and 6LoWPAN for networking, and RPL for mesh routing. A Wi-SUN network operates as a self-forming and self-healing mesh where devices forward traffic for one another, extending coverage and improving reliability without centralized coordination.

These key concepts explain the fundamental structure and behavior of Wi-SUN networks and how they are realized in Digi’s Wi-SUN solution.

Device roles

Devices in a Wi-SUN network take on specific roles, each with different responsibilities in forming and maintaining the mesh:

Border Router

The Border Router is the gateway between the Wi-SUN mesh network and the outside world (typically an IPv6-enabled LAN or the internet). It performs several important functions:

  • Acts as the root of the mesh network.

  • Provides routing to and from external networks.

  • Authenticates and onboards new devices.

  • Maintains network configuration and timing.

All traffic between the Wi-SUN mesh and external systems passes through the Border Router.

Router and Leaf nodes

The Router and Leaf nodes are the field devices of the Wi-SUN mesh. They join the network and take part in the IPv6-based communication that the mesh provides.

  • A Router Node (also known as a Full Function Node, or FFN) is a full participant in the mesh. It can:

    • Route traffic for other nodes.

    • Relay data from child or peer devices.

    • Maintain active participation in the mesh topology.

    Router nodes typically have stable power and good connectivity, making them reliable participants in the mesh backbone.

  • A Leaf Node (also known as a Limited Function Node, or LFN) connects to the network but does not forward traffic for others. These devices:

    • Communicate only with a parent router.

    • May be battery-powered or bandwidth-constrained.

    • Are suitable for end-point sensors or simple actuators.

    Leaf nodes still benefit from mesh reliability but reduce their load by not routing.

To learn more about the devices that take part in the solution, go to Identify the components.

Mesh communication and topology

Wi-SUN networks use a self-forming and self-healing mesh topology. Devices:

  • Discover nearby nodes via beaconing and scanning.

  • Select the best parent or peers based on signal quality and link cost.

  • Dynamically re-route if conditions change (e.g., signal loss, node failure).

This adaptive routing ensures reliable communication across changing environments and allows networks to scale from a few devices to thousands of nodes per PAN.

The mesh operates using regional frequency hopping plans defined by IEEE 802.15.4g, ensuring regulatory compliance and coexistence with other wireless systems.

For more information on Wi-SUN’s mesh communication, see Explore mesh operation.

PAN formation and addressing

A Wi-SUN Personal Area Network (PAN) is created and coordinated by a Border Router, which establishes network parameters and security credentials. When a new device joins, it authenticates using Wi-SUN certificates, receives addressing information, and learns how to communicate with its parent and neighbors.

Each device obtains one or more IPv6 addresses that allow local and global communication through the Border Router.

For more information on Wi-SUN’s use of IPv6 and 6LoWPAN, see See how devices communicate.

Security foundations

Wi-SUN FAN includes a standardized security framework based on certificate-based authentication and link-layer encryption. All devices are provisioned with a unique identity (IDevID) and use mutually authenticated handshakes during network formation. Traffic is protected using AES encryption, and security keys are updated automatically to maintain network integrity.

For more information on Wi-SUN’s security, see Security.