26 lines
1.9 KiB
Markdown
26 lines
1.9 KiB
Markdown
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# Mesh Construction and Communication
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Nodes always power up in Station mode. Each node in the mesh will 1st try to connect to one of the configured WiFi access-points.i
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If the node cannot see any APs, it will next attempt to connect to any nearby nodes.
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A potential node is identified by having a hidden SSID and having a specific MAC address.
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Each node constructs its MAC address by combining its chipId (upper 3 octets) with the mesh password and generating the lower 3 octets.
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The connecting node will check each hidden network's MAC address by calculating the lower 3 octets and verifying that they match the
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AP. All matching nodes are sorted by signal strength, and the node will attempt to connect to each in order.
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Once connected, the connecting node will then open a RCP connection on the specified port, and send the mesh password to the AP. Next the
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node will broadcast a MQTT message about its availability (ex `esp8266-out/bssid/aabbcc=00:11:22:33:44:55`). This message is sent with the
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retain bit set to preserve it on the broker, but it is never consumed by any other nodes. Lastly, the node will start its own AP and begin
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listening for connections from other nodes.
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Each node can only handle 4 incoming commections, and will refuse connections once it has reached the limit. While the max connection
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count is limited by the ESP8266 core code. The ESP8266MQTTMesh library also assumes this limit.
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If a node loses its connection to the AP, it will also shutdown its own AP. This will result in the subsection of the mesh reorganizing
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and rebuilding automatically. It is required that at least one node can see the WiFi AP at any time as the broker must be available
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to handle message passing.
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Mesh nodes cannot generally communicate directly with each other. Instead all messages are passed through the MQTT broker. Nodes
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automatically subscribe to all topics beginning with the `in_topic` value (typically `esp8266-in/`).
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