SkyMote Network Details

Terms

Bridge:  A bridge is used to connect the wireless network to a host via Ethernet or USB.  Each network has only 1 bridge.  The wireless transceiver on a bridge is always on.  A bridge can have up to 16 children (repeaters and motes).

Repeater:  Creates a wireless link between 1 parent and up to 16 children.  The wireless transceiver on a repeater is always on.

Mote:  End-device with sensors and actuators.  Generally operated in sleeping mode, where the device (including wireless transceiver) is shut down most of the time, and wakes up periodically.  A sleeping mote cannot have children.

Network ID:  MAC address of the bridge.  MAC addresses are universally unique in 802.15.4.

Which network will my motes join?

A SkyMote network can be secured with a password, just like a WiFi network. Every bridge, repeater, and mote must share the password. Whether you set a password or not, all wireless transmissions are AES encrypted. The password serves only as a convenience to manage which motes are connected to which network.

No password set

1. If a mote does not have a password set, it will scan for SkyMote networks and join the one with the highest signal strength.

Password set

1. If a mote has a password set, it performs a more sophisticated scan for SkyMote networks.
   1. If the mote finds a bridge or router with about 12 inches (with a very high signal strength), the mote will join that network regardless of password. This is a recovery mode intended for moving a mote to a new network, recovering from a forgotten password, or when replacing a bridge. The signal strength is calculated by received link quality indicator, i.e. LQI, and the LQI must cross a very high threshold to meet this condition.
   2. In the absence of a very close bridge or router, a mote with a password set will join a SkyMote network only after it has verified that the network has the matching password. This process prevents a mote from accidentally joining the wrong network.

Motes ship from the factory with no password set.  If you are not concerned about a mote powering up and finding a stronger network than your own, you can just keep it unlocked. For example, if you have only one SkyMote Bridge, and there aren't any others within range for your motes to join, leave the network unlocked. By contrast, the LabJack office has several separate SkyMote networks, and each mote is locked to a specific network. That way, motes don't accidentally join the wrong bridge. If we change our mind and want to switch a mote to a new network, we reset the mote next to the new bridge and update its password.

Joining details

Future Possibility:  Parents can have a whitelist (allow only these child MAC addresses) and a blacklist (refuse these child MAC addresses).  Both lists default to empty, which means allow any child to join.

Unjoining:  A child can unjoin itself or be unjoined by its parent.  A child unjoins itself if it experiences too many failed communication cycles.  A parent unjoins a child if it experiences too many failed attempts to send a command to a child, or if too much time passes without the parent receiving any communication from the child.

numChildCommRetries:  Within a single communication cycle, this is how many times a child will retry if a communication failure happens.  If this limit is hit, the communication cycle will be declared failed.

numChildCommFailures:  Number of failed communication cycles allowed before the child unjoins from the network.

Network size

The network device limit (bridge + repeaters + motes) is currently set at 128.