How is the bluetooth low energy pairing method chosen Android

Question

I am a little confused as to what level the Android or peripheral device requests the bluetooth low energy pair request type. Is this in the application layer when I initiate the connection via device.connectGatt(context, false, gattCallback) or would this be the job of the peripheral to suggest the type?

How can someone choose between Just Works , Numeric Comparison , Passkey Entry and Out of Band ?

Answer 1

Both devices exchange their IOCapabilities at the beginning of the pairing process. The initiator send a IOCapabilityRequest and the responding device answers with a IOCapabilityResponse.

As the name says, the IO Capabilites contain data about what the device can show to the user. This can be one of "Display Only", "Display Yes/No", "Keyboard Only", "NoInputNoOutput", "KeyboardDisplay".

According to what both devices can do, they chose the method, see here:

https://blog.bluetooth.com/bluetooth-pairing-part-4

and

https://blog.bluetooth.com/bluetooth-pairing-passkey-entry