OPENTHREAD_CONFIG_SUPERVISION_MSG_NO_ACK_REQUEST

[Ewout]

I have been trying to understand Child Supervision. Part of the documentation that I have read is:

https://openthread.io/guides/build/features/child-supervision

At the bottom of the page it explains that one can set OPENTHREAD_CONFIG_SUPERVISION_MSG_NO_ACK_REQUEST: "Set to 1 to clear/disable the 802.15.4 ACK request in the MAC header of a supervision message". 

I had assumed that, in child supervision mode, the parent too needs to have an idea whether the child is still there. From the documentation my assumption was that that would be the responded ACK to a Child Supervision message.

So my question, based on the documentation it is clear what Child Supervision message does on the child's side, but how does the parent know that the child is still there or not? I am interested both in the case where OPENTHREAD_CONFIG_SUPERVISION_MSG_NO_ACK_REQUEST is 0 and 1.

Thanks in advance!

[Elfving]

I've forwarded the question to someone who knows Thread better than I, but my first impression is that this is the reason why OPENTHREAD_CONFIG_SUPERVISION_MSG_NO_ACK_REQUEST is necessary. The parent might want to know about the presence of the child, and that is why you can set this to 0. You can set this to 1 however, if you do not think the parent needs to know. And arguably it doesn't because the only action to be taken when the child is lost is from the childs side: initiating the MLE Attach process. Do you agree that the parent doesn't really need to know?

Regards,

Elfving