Features

BlueRange Mesh has inbuilt time synchronization. A gateway or smartphone can act as a synchronisation device to send a unix timestamp to one node in the mesh. This node will then take care that this timestamp is synchronized to all other nodes in the mesh. If any number of nodes are rebooted, the time will be synchronized again if there is at least one node that still has the current time. By using a counter value, we make sure that the latest timestamp will be synchronized and that the time can be corrected in both directions. The time is always synchronized between two partners in a kind of handshake where first the time is sent to the other node and next, an offset is sent to account for the delay in sending that message. Further documentation can be found here.

Depending on the configuration of the nodes in a network, the connection MTU (Maximum Transmission Unit) might only allow for a packet size of 20 bytes payload. As you will probably need to send bigger packets from time to time, we implemented automatic packet splitting. A packet can be queued with a size of up to 200 bytes and is then split automatically before it is sent to the next node at which point it is automatically reassembled. This process also makes sure that a packet uses the maximum possible MTU available.

Once we attach a Gateway to the Mesh, we might want to send messages on a direct route to that Gateway. Or maybe, we simply want to know if a Gateway is currently available in the mesh. Sink determination determines the number of hops to the Gateway on each node. During clustering, a new node performs a handshake with its partner node and exchanges information about the network structure. This includes the cluster size and also the master bit that is used to determine which cluster must dissolve if a connection is lost. This handshake also includes the number of hops to the sink (MeshGateway). This information is also included in the clusterInfoUpdate packets that notify all nodes about changes in the network.

If a sink is available through a connection, the number of hops to this sink will be sent with these packets. The sink itself has 0 hops to the sink. If there is no sink available, it is denoted with -1.

BlueRange Mesh relies an standard BLE GAP connections which have a configurable interval and timeout. These can be chosen depending on the use-case for either high throughput or low power consumption. If a small timeout is chosen and the environment has high radio interference, it can happen that these GAP connections are disconnected. In these cases, there is an extended timeout in which BlueRange Mesh will try to reestablish the GAP connection multiple times until it succeeds. Packets will stay in the queue and will be sent after the connection was reestablished. This means, that aside from a higher latency, no packet loss will occur.

The hardware watchdog is configured to restart a node after a certain time if it doesn’t receive a keep alive packet from the gateway in the meantime. This is the last fallback to recover a node if there is some critical unknown issue. It is also possible to configure the Watchdog to work without a Gateway, it will then monitor the behaviour of the node itself.

It is possible to configure the watchdog to use safe boot. In safe boot mode, the node will boot up without loading any persistant configuration. This also means that the node will not be enrolled in this mode, but it will reboot in normal mode after the watchdog triggers again. This makes it possible to rescue a node that received a faulty persistent configuration.