Question about IV index and sequence number SDK v4.1

[huybk213]

Dear all,

I have a question about IV index and sequence number in mesh network.

If i have 3 nodes success provisioned.
I will only power on 2 active node ( node 1 and node 2), power off one other node ( node 3), and let it run a a few months.
I think IV index and sequence number will be increase and overflow.
After sequence number overflow, Mesh network will update new IV index and reset sequence number for node 1 and node 2.

If after a few month, we power on node 3, but i think node 3 and node 1-2 has difference IV indev. Node 3 can not communicate with other node.
So i have a 3 questions.
1. How can node 3 update IV index?
2. Is there any function in Mesh SDK support node 3 update IV index or listen IV index beacon?
3. How long interval node 1 and node 2 send secure beacon with IV index information into mesh network?
4. Can you recommend a solution for that problems?

Best regards.

[Hung Bui]

Hi Huy, 

If you have a look at the Bluetooth Mesh Spec v1.0.1 at section 3.8.4 you can find this: 

If a node is absent from a mesh network for a period of time, it can scan for Secure Network beacons (see Section 3.10.1) or use the IV Index Recovery procedure (see Section 3.10.6), and therefore set the IV Index value autonomously.

Node 3 when it couldn't communicate with other node would need to listen to Secure Network beacons. After it receive a Secure Network Beacon it will follow the IV Index Recovery procedure to update the IV index hence join the network again. 

This is already handled in net_beacon.c module. By default the Secure Network beacon is sent every 10 seconds. So on average Node 3 would need to listen around 5 seconds before it can catch the Secure Network beacon and start communicate again. 

[huybk213]

Dear Mr Hung,

I understood your answer

If node 3 need to listen secure network beacon, how can i do this? It listen beacon by default or i need to trigger an event to put node 3 enter listen mode?

Thanks.