ZigBee radio channel change

[Laura M]

Hello,

We developed with nRF5240 using nRF5 SDK as zigbee coordinator and I have some questions about channel change mechanism:

1. By choosing 'coordinator' as network role at startup, is this automatically also the network channel manager as explained in Annex E of Zigbee specification https://zigbeealliance.org/wp-content/uploads/2019/11/docs-05-3474-21-0csg-zigbee-specification.pdf ?
2. When a high value of transmit failures is detected, is channel scan done? Is channel changed?
3. Do you manage the reception of Mgmt_NWK_Update_notify? Which actions are performed?
4. In Zigbee spec about transmit failures, there is written: "the network manager would report to the local application using Mgmt_NWK_Update_notify and the application can force a channel change using the Mgmt_NWK_Update_req.". Do you ever notify application about this through Zigbee signal handler or any callback? Do you implemented a function that I can use to send Mgmt_NWK_Update_req to force channel change?

I've read another question about the same topic:  https://devzone.nordicsemi.com/f/nordic-q-a/94366/zigbee-radio-channel-selection-and-change-during-run-time/398143 
But I couldn't find the answers.

Best regards.

Laura

[Marte Myrvold]

Hi Laura,

By choosing 'coordinator' as network role at startup, is this automatically also the network channel manager as explained in Annex E of Zigbee specification https://zigbeealliance.org/wp-content/uploads/2019/11/docs-05-3474-21-0csg-zigbee-specification.pdf ?

Yes, the coordinator will be the network manager. 

When a high value of transmit failures is detected, is channel scan done? Is channel changed?

This is correct. Both routers and coordinators will track transmit failures. If the number of transmit failures is too high, then the coordinator will perform energy scans on the different channels. The network manager (coordinator) can then decide to change channel.

Do you manage the reception of Mgmt_NWK_Update_notify? Which actions are performed?

This is handled internally by the stack. I am not sure exactly which actions the network manager performs in the ZBOSS stack, since there are no strict specifications on how a network manager must handle this, but I will ask the development team.

In Zigbee spec about transmit failures, there is written: "the network manager would report to the local application using Mgmt_NWK_Update_notify and the application can force a channel change using the Mgmt_NWK_Update_req.". Do you ever notify application about this through Zigbee signal handler or any callback? Do you implemented a function that I can use to send Mgmt_NWK_Update_req to force channel change?

All of this is handled internally by the stack, and there is no signal sent to the signal handler about this. However, you can manually send a Mgmt_NWK_Update_req with zb_zdo_mgmt_nwk_update_req(). If you set ScanDuration to 0xfe then the Mgmt_NWK_Update_req will be a request to change channel.

Best regards,

Marte

[Laura M]

Hello Marte,

thank you for the reply.

Regarding  zb_zdo_mgmt_nwk_update_req function, is it enough to call it in order to notify devices about the channel change and also to change channel? Take into account that I'm developing a Zigbee coordinator device.

If that function isn't enough, is there another function to change channel? I've tried to use nrf_802154_channel_set function but channel didn't change, as I could see from a radio sniffer. Please consider that I'm trying to change channel at run time.

Best regards

Laura

[Marte Myrvold]

Hi Laura,

Laura M said:

Regarding  zb_zdo_mgmt_nwk_update_req function, is it enough to call it in order to notify devices about the channel change and also to change channel?

This should be enough, but I have not tested it myself.

Laura M said:

If that function isn't enough, is there another function to change channel? I've tried to use nrf_802154_channel_set function but channel didn't change, as I could see from a radio sniffer

I am not aware of any other functions other than zb_zdo_mgmt_nwk_update_req() or nrf_802154_channel_set(). The latter should work, I just tested and verified this myself. However, I would not recommend using this, as it will change the 802.15.4 channel without informing the Zigbee stack. So the Zigbee stack will still believe that it is operating on the previous channel, and it will not inform any other devices about the channel change.

Best regards,

Marte

[Laura M]

Hello,

I am writing again about this topic to have a clarification.

1. When you write "The network manager (coordinator) can then decide to change channel", who is responsible for changing channel? ZBOSS stack, Nordic stack, or user application?
2. How is the application notified about channel been changed, if channel change is managed by stack? Or how is it notified about a request to change channel, if the channel change needs to be managed by user application?

Best,

Laura

[Marte Myrvold]

Hi Laura,

Laura M said:

When you write "The network manager (coordinator) can then decide to change channel", who is responsible for changing channel? ZBOSS stack, Nordic stack, or user application?

This is done by the ZBOSS stack.

Laura M said:

How is the application notified about channel been changed, if channel change is managed by stack? Or how is it notified about a request to change channel, if the channel change needs to be managed by user application?

The application does not need to handle this, as it should be handled automatically by the ZBOSS stack. Thus, the application is not notified about the channel change.

Best regards,
Marte

[Laura M]

Hello Marte,

thank you for your answers. Related to this topic, I am not sure how to solve an issue I face: devices in our meshes falling off the network and requiring re-commissioning, because they never received the command to move to new channel.

I’ve been running the following tests to understand what is going on with ZBOSS stack:

1. Nordic as coordinator broadcasting Mgmt_NWK_Update_req to change channel.
   The request is sent through zb_zdo_mgmt_nwk_update_req function as you suggested.
   Result is Nordic remaining in previous channel while routers moving to new channel.
   I was expecting Nordic to change channel too.
2. Nordic as router sending to Nordic as coordinator Mgmt_NWK_Update_req to change channel. Nordic as router is running CLI example code from Nordic nRF5 SDK for Thread and Zigbee v4.1.0.
   Result is Nordic as coordinator changing channel without notifying routers within the network and Nordic as router not changing channel.
   I was expecting Nordic as coordinator not changing channel at all or changing channel notifying routers within the network.

I used Nordic nRF5 SDK for Thread and Zigbee v4.1.0 and then I repeated tests with v4.2.0 with same results.

I've also performed some tests with nrf_802154_channel_set but I saw that new channel isn't stored and when nordic reboots it moves to previous channel.

Can you please bring clarity on this topic and suggest improvements I can implement.

Thank you in advance.

Best regards,

Laura