Rx-off-when-idle Children should periodically send Child Upgate Request to their parent

[jinpeng1989]

The Thread Specification defines: Rx-off-when-idle Children SHOULD also periodically resynchronize by sending a Child Update Request to their parent to avoid cases where the MAC Data Request is acknowledged erroneously by the receiver.

However, I have not observed this behavior from SED devices. Does OpenThread implement this feature? What is the sending period?

[jwhui]

Thread 1.4 Section 4.6.3.5 specifies Child Supervision:

The Child Supervision function is an alternative to the periodic keep-alive message sent by a Child. When Child Supervision is enabled, the burden of sending periodic keep-alive messages is placed on the Parent. This helps Sleepy End Devices (SEDs) to operate more efficiently and conserve energy. A Thread Router MUST support Child Supervision in the Parent role; and an rx-off-when-idle MTD MAY support it in the Child role.

OpenThread implements the Child Supervision feature.

[jinpeng1989]

May I conclude that? SED must support and enable Child Supervision.

[jwhui]

Yes, the SED itself must also support Child Supervision. OpenThread enables Child Supervision on child by default.