TTL - Hop Count

[Brijesh]

Imagine i have a client which sends message to a gateway and i set a TTL for the shortest path . If one of the node is not functioning how will the mesh reroute the message.I have seen health model but i couldn't understand what it said.

[Joakim Jakobsen]

Hi. 

The message you send will be broadcasted to all the nodes in range. The message will then be relayed by all of the relay nodes that receives it. 
So if you have one node that fails, the other relay nodes should be able to relay the message and find another route to the gateway.

However, if the TTL is set to a minimum (with the shortest path in mind) and any other route has more hops than the TTL allows, then the Mesh will not be able to relay the message to it's destination.

Best regards, 
Joakim.

[Brijesh]

so the health model will be useless . Can u please tell me in layman terms what is a health model used for.. I read it sends out some heart beat messages bt i didnt understand to who, does it send that.

[Joakim Jakobsen]

Hi.

This should be explained well in the Mesh Specification:

"Health messages are used to monitor states that determine the physical condition of a node."

Note that there is a difference between the health messages and heartbeat messages;
https://devzone.nordicsemi.com/f/nordic-q-a/43625/mesh-heartbeat-vs-health

Best regards,
Joakim

[Brijesh]

ok so u mean that the health model shud also be assigned a publish address so that it can publish its health status to a specific node.

[Joakim Jakobsen]

That is correct. 

You can use both a group address or a unicast address for this. When using a group address you can have several nodes subscribing to the given address, i.e the message can be sent to several nodes. Using a unicast address will send the message to one specific node. 

Best regards, 
Joakim