This example is like the bt_thermometer_client - bt_thermometer example pair with multi-radio
support and bonding. The central.py script corresponds to the bt_thermometer_client and acts
as a virtual access point made of several radios. The peripheral.py script corresponds to the
bt_thermometer example and implements multiple heart rate sensors at once.
Each radio board in the central.py forms a physical access point. The access points are managed
by a single network coordinator. Scanning for heart rate sensors is performed for 3 seconds in every
30 seconds or immediately when a device disconnects. When a heart rate sensor is found, the nearest
AP (i.e. the one with the largest RSSI) connects to it. Every AP uses the same identity. I.e., all
heart rate sensors seem to be connected to the same virtual access point.
Bonding is performed by the access points using external bonding database feature. This means that the user application is responsible for storing the bonding keys provided by the Bluetooth stack and provide those keys when requested by the stack. In this example, bonding data is stored in a json file between sessions.
Bonding keys are sensitive data therefore both the bonding data storage file and the NCP communication between the host SW and the target FW shall be encrypted when developing products that use the external bonding database feature.
The external bonding database Bluetooth feature is not part of the Bluetooth - NCP example by default, it has to be added manually when creating the project for the access points. Heart rate sensor devices shall be used with the default Bluetooth - NCP example without external bonding database.