Add `class_c_enabled` for class C mode

[johanstokking]

Summary

Add class_c_enabled to the current MAC state indicate whether class C is enabled for 1.0.x devices.

Add class_c_always_enabled to the end device (stored in NS). This should be taken from a new field in the Device Profile (part of TS002 1.2).

Current Situation

Currently, NS uses the end device's supports_class_c flag for 1.0.x devices.

Why do we need this? Who uses it, and when?

We need the class_c_enabled flag to indicate that class C is actually enabled right now. This is used for downlink scheduling.

We need the class_c_always_enabled flag to set the class_c_enabled flag to an initial value.

In 1.1 or higher, DeviceModeInd still takes precedence.

Proposed Implementation

The flag supports_class_c should only be used to indicate whether the end device implements class C support. This is probably not relevant for the NS (for now). So what should be removed, is NS logic that uses supports_class_c.

Instead, the logic to check whether class C is enabled should be determined based on this new flag in the MAC state.

The class_c_always_enabled flag is simply added to the end device itself. It serves as a default for class_c_enabled in a new MAC state. Again, only for 1.0.x devices.

Contributing

• [X] I can help by doing more research.
• [X] I can help by implementing the feature after the proposal above is approved.
• [X] I can help by testing the feature before it's released.

Code of Conduct

• [X] I agree to follow TTN's Community Code of Conduct.

[adriansmares]

The class_c_always_enabled flag is simply added to the end device itself. It serves as a default for class_c_enabled in a new MAC state. Again, only for 1.0.x devices.

In the absence of class_c_always_enabled, the default value should still be true for backwards compatibility, right ?

Also, since there is no DeviceModeInd in 1.0.x, how would a device signal to the NS the switch ?

[johanstokking]

Also, since there is no DeviceModeInd in 1.0.x, how would a device signal to the NS the switch ?

The application does that, so that would go via the AS. So the AS would be able to set this field on the NS, autonomously based on payload, so without forwarded auth from a user request.

[KrishnaIyer]

This will wait until there's demand.