Enable Child Supervision

[ksathara]

Hi,
our system is made out of one FTD as a coap server and many SEDs as coap clients. We have seen rarely some clients drop off from the child table of the FTD. The clients battery seems ok. Also the RSSI seems well within budget.

Since we couldn't figure out what is causing this, as a secondary measure, we are planning to implement 'Child Supervision'.
I have few questions.

1. It is mentioned to enable 'OPENTHREAD_CONFIG_CHILD_SUPERVISION_ENABLE', in child_supervision.h in SDK. I dont think changing SDK content is a good idea as if the SDK is updated, we will loose all that. Is there a way to implement child supervision from application side?

2. What is to be done from FTD side?

3. What is to be done from SED side?

Thanks,
Kaushalya

[jwhui]

Child Supervision feature is now enabled by default since:

• [child-supervision] mechanism to inform interval from child to parent #7993

[abtink]

Child Supervision was earlier a custom enhancement/feature provided by the OpenThread stack. It is now adopted by the Thread spec and is a required feature in the Thread 1.3.0 Consequently, in the main OT repo, you'll no longer find the OPENTHREAD_CONFIG_CHILD_SUPERVISION_ENABLE configuration option (see #7993). If you update to later OpenThread stack commits, this feature will be enabled and used.

---

While slightly outdated, this guide may still offer insights:

• Child Supervision.
• (the source code thread/child_supervision.hpp)

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I dont think changing SDK content is a good idea as if the SDK is updated, we will loose all that. Is there a way to implement child supervision from application side?

Technically possible to do so, but I won't recommend it.

[jwhui]

Nordic SDK 2.3.0 documentation seems to indicate that the Child Supervision feature is enabled.

OpenThread does not currently provide an API to evict a child table entry.

[ksathara]

Hi,
The SED doesn't seem to get the child supervision packets send by its paired FTD, when it has a router in the middle, who is 'not' supporting child supervision. I see my SED logs say it's child supervision times out. But when the SED is directly connected to the child supervision enabled FTD, everything works. Doesn't the parent's child supervision message routes through other routers with this feature disabled?
Cheers,
Kaushalya

[abtink]

Child supervision operates directly between a parent and its child, which always have a direct link to each other.

If a parent node uses an older version without supervision support, the feature will not function. In this case, the child should automatically fall back to periodically sending "Child Update Requests" to maintain connectivity with its parent (the child supervision feature implements this fallback).

[ksathara]

Hi Abtink,
In a multi hop scenario, the parent means the router to which the SED is immediately connected? Or in other words the router who has the SED in it's child table?
Cheers,
Kaushalya

[jwhui]

The parent is the the router that the child directly attaches to.

https://openthread.io/guides/thread-primer/node-roles-and-types

[ksathara]

Hi guys,

Is this a child supervision message send by a parent? The parent is 0x2c00 (02:5b:eb:ab:b8:58:00:6e) and the child is 0x2c01 (d2:fc:2e:43:b4:c2:e8:76).

Cheers,
Kaushalya

[jwhui]

Yes, the parent sends Child Supervision messages to validate that the child still exists.