Some questions about Child Supervision

RE: Some questions about Child Supervision

Edvin — Fri, 21 Jan 2022 13:51:56 GMT

The thing with SEDs is that they are Sleeping, and while they are sleeping the radio is off. Hence, there is no way to reach the SED when it is sleeping. Therefore you need to make sure that the child wakes up more often than OPENTHREAD_CONFIG_CHILD_SUPERVISION_CHECK_TIMEOUT. To be sure, perhaps try to make it wake up twice every timeout interval.

[quote user="Edvin Holmseth"]The poll_period is something you set when you enter the SED state. Perhaps you can show some snippets from where you are doing this?[/quote]

Did you check this?

RE: Some questions about Child Supervision

taoyinzhou — Fri, 21 Jan 2022 08:54:48 GMT

The documentation from openthread on:

OPENTHREAD_CONFIG_CHILD_SUPERVISION_INTERVAL.

"If a parent router does not transmit to its child SED within the OPENTHREAD_CONFIG_CHILD_SUPERVISION_INTERVAL, the parent router enqueues and sends a Child Supervision message to the child SED" It explains what the Router does in the Child Supervision function.

You said if SED don't wake up within the interval, then the parent can't send a ping until it is awake again.It seems contradictory.

According to the description in the document, I understand that if the router doesn't have a packet to send to SED within the OPENTHREAD_CONFIG_CHILD_SUPERVISION_INTERVAL, it will send a packet, regardless of whether SED accepts it or not, but I don't see the message. My confusion is that the Router did not send this packet.

Does the Router have to wait for the child to wake up and send a notification to the Router that it is awake? It seems that Child Supervision is not efficient.

RE: Some questions about Child Supervision

Edvin — Mon, 17 Jan 2022 13:44:15 GMT

Please see the documentation from openthread on:

OPENTHREAD_CONFIG_CHILD_SUPERVISION_CHECK_TIMEOUT

This is the child's way of knowing whether it is still connected or not, while the OPENTHREAD_CONFIG_MLE_CHILD_TIMEOUT_DEFAULT is the parent/router's way of knowing whether the child is alive. If more time than this passes, then the child is considered disconnected.

OPENTHREAD_CONFIG_CHILD_SUPERVISION_INTERVAL

is the interval of which the parent tries to ping the child.

So these are similar, but they have different uses.

[quote user="winik"]When the router does not send a message to SED within this time, the router will send such a message to SED[/quote]

I don't understand exactly what you mean by this, but I guess you don't see the messages in the sniffer trace. Do you see them if the node is just a child, but not an SED? And again, What is the sleep/wake up interval of your SEDs? The reason I keep asking about this is that when an SED goes to sleep, the parent has no way of reaching it before it wakes up, so if you don't wake up within the interval, then the parent can't send a ping until it is awake again.

RE: Some questions about Child Supervision

taoyinzhou — Mon, 17 Jan 2022 08:46:03 GMT

Thank you for your reply.

On the first question, I feel there is something wrong with the answer.The Child Supervision setup for timeouts should be this macro: OPENTHREAD_CONFIG_CHILD_SUPERVISION_CHECK_TIMEOUT.
OPENTHREAD_CONFIG_MLE_CHILD_TIMEOUT_DEFAULT works in connection timeouts with the router, such as age in the figure below.I think the functions of the two are repetitive, so I want to know their relationship

The second issue, when I say it doesn't work, is that there's a parameter OPENTHREAD_CONFIG_CHILD_SUPERVISION_INTERVAL that doesn't work. If I understand correctly, this is for the router. When the router does not send a message to SED within this time, the router will send such a message to SED. I did not see such a packet in the packet capture，the OTBR did not send a packet to SED after the time expired.

RE: Some questions about Child Supervision

Edvin — Fri, 14 Jan 2022 07:30:43 GMT

[quote user=""]1.What is the relationship between child supervision and the OPENTHREAD_CONFIG_MLE_CHILD_TIMEOUT_DEFAULT function? Is it a low-power alternative?[/quote]

Child supervision timeout is the time it takes from radio silence until a child is considered lost in the network (disconnected). This is in case of the child runs out of battery, or comes out of range, or is turned off. This setting is set using OPENTHREAD_CONFIG_MLE_CHILD_TIMEOUT_DEFAULT.

[quote user=""]2.Why does the function of Child Supervision not take effect on OTBR and RCP? Could you please tell me which configuration items need to be enabled?[/quote]

What do you mean by "not take effect on OTBR and RCP"? Do you mean that you set the OPENTHREAD_CONFIG_MLE_CHILD_TIMEOUT_DEFAULT on your OTBR, and it doesn't change the behavior on the SED? As mentioned in a previous reply, this setting doesn't change how often the SED will wake up, but how long it takes until it is considered lost from the network.

[quote user=""]3.If the OPENTHREAD_CONFIG_CHILD_SUPERVISION_MSG_NO_ACK_REQUEST option is enabled, does that mean the SED is receiving the message from the OTBR and does not need to respond with an ACK?[/quote]

Yes and no. All messages are ACKed on the 802.15.4 MAC layer, but this setting says that it doesn't need to be ACKed by the application.

As an example, if a light switch sends a message to a light bulb, and they are not within range, then the message will be sent via another node. Let us call light switch node A, middle node is node B, and light bulb is node C. A wants to send a message to C, without acking:

A->B payload

B->A ack (MAC layer)

B->C payload

C->B ack (MAC layer)

However, if this message requires ACKs, then it would be:

A->B payload (C should turn on the light)

B->A ack (MAC layer)

B->C payload

C->B ack (MAC layer)

C->B application ack (I have received the message and turned on the light)

B->C ack (MAC layer)

B->A application ack (I have received the message and turned on the light)

A->B ack (MAC layer).

Best regards,

Edvin

RE: Some questions about Child Supervision

taoyinzhou — Thu, 13 Jan 2022 09:10:56 GMT

But I asked about the function of Child Supervision.

And my three additional questions haven't been answered.

RE: Some questions about Child Supervision

Edvin — Tue, 11 Jan 2022 14:37:48 GMT

Ok. Does that mean that your questions were answered? If not, can you please clarify what you want to know at this point?

Best regards,

Edvin

RE: Some questions about Child Supervision

taoyinzhou — Tue, 11 Jan 2022 03:17:24 GMT

I'm sorry. I made a mistake.

Because of the need to control the power consumption of the device，when the device needs to communicate with the Internet, I set poll_period to 2000. When the device needs to sleep, I set poll_period to 64800000.

I use otLinkSetPollPeriod() to set poll_period.

RE: Some questions about Child Supervision

Edvin — Mon, 10 Jan 2022 14:22:00 GMT

Hello,

The OPENTHREAD_CONFIG_MLE_CHILD_TIMEOUT_DEFAULT 600

doesn't set the sleep interval of the child. It decides how long a child has to be "radio silent" before it is considered lost for the network. The poll_period is something you set when you enter the SED state. Perhaps you can show some snippets from where you are doing this?

Best regards,

Edvin

RE: Some questions about Child Supervision

taoyinzhou — Mon, 10 Jan 2022 11:41:41 GMT

I use the following two options to make the device SED:

CONFIG_OPENTHREAD_MTD=y

CONFIG_OPENTHREAD_MTD_SED=y

sleep interval option:

#ifndef OPENTHREAD_CONFIG_MLE_CHILD_TIMEOUT_DEFAULT
#define OPENTHREAD_CONFIG_MLE_CHILD_TIMEOUT_DEFAULT 600
#endif

RE: Some questions about Child Supervision

Edvin — Mon, 03 Jan 2022 11:46:11 GMT

Hello,

Your Sleepy End Device, is that something that you are developing as well, or is it an off the shelf product?

If it is something you are developing, how did you set it up to be an SED? Do you know what sleep interval you are using on the SED?

Best regards,

Edvin