Espressif ESP32-S2 Programming Manual page 1320

Chapter 4. API Guides
Fig. 5: ESP-WIFI-MESH Tree Topology
these variables can be configured to limit the size of the network.
Node Types
Root Node: The root node is the top node in the network and serves as the only interface between the ESP-WIFI-
MESH network and an external IP network. The root node is connected to a conventional Wi-Fi router and relays
packets to/from the external IP network to nodes within the ESP-WIFI-MESH network. There can only be one
root node within an ESP-WIFI-MESH network and the root node's upstream connection may only be with the
router. Referring to the diagram above, node A is the root node of the network.
Leaf Nodes: A leaf node is a node that is not permitted to have any child nodes (no downstream connections).
Therefore a leaf node can only transmit or receive its own packets, but cannot forward the packets of other nodes.
If a node is situated on the network's maximum permitted layer, it will be assigned as a leaf node. This prevents
the node from forming any downstream connections thus ensuring the network does not add an extra layer. Some
nodes without a softAP interface (station only) will also be assigned as leaf nodes due to the requirement of a softAP
interface for any downstream connections. Referring to the diagram above, nodes L/M/N are situated on the networks
maximum permitted layer hence have been assigned as leaf nodes .
Intermediate Parent Nodes: Connected nodes that are neither the root node or a leaf node are intermediate parent
nodes. An intermediate parent node must have a single upstream connection (a single parent node), but can have
zero to multiple downstream connections (zero to multiple child nodes). Therefore an intermediate parent node
can transmit and receive packets, but also forward packets sent from its upstream and downstream connections.
Referring to the diagram above, nodes B to J are intermediate parent nodes. Intermediate parent nodes without
downstream connections such as nodes E/F/G/I/J are not equivalent to leaf nodes as they are still permitted to
form downstream connections in the future.
Idle Nodes: Nodes that have yet to join the network are assigned as idle nodes. Idle nodes will attempt to form
an upstream connection with an intermediate parent node or attempt to become the root node under the correct
circumstances (see Automatic Root Node Selection). Referring to the diagram above, nodes K and O are idle nodes.
Beacon Frames & RSSI Thresholding
Every node in ESP-WIFI-MESH that is able to form downstream connections (i.e. has a softAP interface) will
periodically transmit Wi-Fi beacon frames. A node uses beacon frames to allow other nodes to detect its presence
Espressif Systems 1309 Release v4.4
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