Custom radio protocols
A common topology for IoT networks is a star network, ie. a single hub or gateway which bridges the physical devices and the rest of the world. The network itself can be of any kind but from the outside it looks like a star network:
A two-tiered networking model can make sense for many reasons – running a custom radio protocol can be very efficient for a low number of devices, the range might not be sufficient for a wide area network and the hardware can be made cheaper by using low-cost components for local communication or you might want some level of local autonomy for availability.
The gateway protocol used by Span is quite simple and allows you to manage multiple devices behind a gatway while still providing augmented metadata and message retention.
A single device in Span can be configured to use multiple gateways if you have multiple protocols or a redundant set-up.
A real-world example is documented in this blogpost