IV Index update LPN

[BubDev]

Hello,

What happens with the LPN firmware if it currently has an IV index of 0 and loses power for an extended period of time. When it gets power, the network that it is on has move all the way to IV index 2.

Will it be able to get a friend?

Will the friend be able to update the IV index of the LPN to 2?

Can the LPNs do an IV index recovery procedure like normal mesh nodes can?

[Hung Bui]

Hi Brad, 
Please have a look at section 3.10.6 IV Index Recovery procedure in the spec: 

The Low Power Node if losing IV index update would need to listen for at least 5 seconds to catch the Secure Network Beacon. If it couldn't listen for such long, it should wake up at least once per 96 hours to get the update from the friend before the IV Update procedure finished. 

[BubDev]

Thanks for the response.

So what does the current LPN example do?

Does it listen for a beacon or does it rely on a friend to update it?

I tested with the example LPN and if it currently has an IV index of 0 it is not able to establish a friendship with any device that has an IV index greater than 1. This means it will never get the IV index update and no longer be able to communicate with devices on the network if it misses 2 IV index updates. 

[Hung Bui]

My understanding is that after the IV Index update process is finished, the LPN will not be able to communicate with the friend node and will need to listen for Secure Network beacon to update it. This beacon can be from any node, not just the friend node. 

[BubDev]

I dont think beaconing is enabled in the LPN example. 

How would the LPN know if it missed an IV index update if it doesn't have a friend?

Maybe the LPN example listens for a beacon after it doesn't get a friend update for more than 96 hours?

[Hung Bui]

I would need to double check with the team, but you can find in the LPN code beacon_packet_in() in beacon.c that process incoming beacons, including the net beacon. 
The question is if this function (as declared as  handler for AD_LISTENER) will be executed when the LPN lost friendship or not. 

[Hung Bui]

I got the confirmation, there is a definition 
MESH_FEATURE_LPN_ACT_AS_REGULAR_NODE_OUT_OF_FRIENDSHIP
If that set to 1, it will act as regular node and the scanner will be executed when the friendship is terminated. Have a look at event_send() in lpn.c . It will enable scanner and the AD_LISTENER will take effective. 

But be careful when using this as it will draw lots of current as a normal mesh node.