Heartbeat
The Heartbeat feature provides functionality for monitoring Bluetooth Mesh nodes and determining the distance between nodes.
The Heartbeat feature is configured through the Configuration Server model.
Heartbeat messages
Heartbeat messages are sent as transport control packets through the network, and are only encrypted with a network key. Heartbeat messages contain the original Time To Live (TTL) value used to send the message and a bitfield of the active features on the node. Through this, a receiving node can determine how many relays the message had to go through to arrive at the receiver, and what features the node supports.
Available Heartbeat feature flags:
Heartbeat publication
Heartbeat publication is controlled through the Configuration models, and can be triggered in two ways:
- Periodic publication
The node publishes a new Heartbeat message at regular intervals. The publication can be configured to stop after a certain number of messages, or continue indefinitely.
- Triggered publication
The node publishes a new Heartbeat message every time a feature changes. The set of features that can trigger the publication is configurable.
The two publication types can be combined.
Heartbeat subscription
A node can be configured to subscribe to Heartbeat messages from one node at the time. To receive a Heartbeat message, both the source and destination must match the configured subscription parameters.
Heartbeat subscription is always time limited, and throughout the subscription period, the node keeps track of the number of received Heartbeats as well as the minimum and maximum received hop count.
All Heartbeats received with the configured subscription parameters are passed
to the bt_mesh_hb_cb::recv event handler.
When the Heartbeat subscription period ends, the
bt_mesh_hb_cb::sub_end callback gets called.