Espressif ESP32-S2 Programming Manual page 1321

Chapter 4. API Guides
and know of its status. Idle nodes will listen for beacon frames to generate a list of potential parent nodes, one of
which the idle node will form an upstream connection with. ESP-WIFI-MESH uses the Vendor Information Element
to store metadata such as:
• Node Type (Root, Intermediate Parent, Leaf, Idle)
• Current layer of Node
• Maximum number of layers permitted in the network
• Current number of child nodes
• Maximum number of downstream connections to accept
The signal strength of a potential upstream connection is represented by RSSI (Received Signal Strength Indication)
of the beacon frames of the potential parent node. To prevent nodes from forming a weak upstream connection,
ESP-WIFI-MESH implements an RSSI threshold mechanism for beacon frames. If a node detects a beacon frame
with an RSSI below a preconfigured threshold, the transmitting node will be disregarded when forming an upstream
connection.
Panel A of the illustration above demonstrates how the RSSI threshold affects the number of parent node candidates
an idle node has.
Panel B of the illustration above demonstrates how an RF shielding object can lower the RSSI of a potential parent
node. Due to the RF shielding object, the area in which the RSSI of node X is above the threshold is significantly
reduced. This causes the idle node to disregard node X even though node X is physically adjacent. The idle node will
instead form an upstream connection with the physically distant node Y due to a stronger RSSI.
Note: Nodes technically still receive all beacon frames on the MAC layer. The RSSI threshold is an ESP-WIFI-
MESH feature that simply filters out all received beacon frames that are below the preconfigured threshold.
Preferred Parent Node
When an idle node has multiple parent nodes candidates (potential parent nodes), the idle node will form an upstream
connection with the preferred parent node. The preferred parent node is determined based on the following criteria:
Espressif Systems
Fig. 6: ESP-WIFI-MESH Node Types
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