[NRF MESH] What will happen if a node receive two or more messages at the same time

[William Nguyen]

Hi all, I am working on a mesh project. I've read Mesh Technology Overview written by Martin and I wonder what will happen if a node receive two or more messages at the same time.

For instance, in this Figure, what happen if the Light Bulb 3 receive messages of two Switches above? I mean exactly the same time pressed, the same time remaining of the message coming to Light Bulb. Will it happen? And how can mesh control this case? 

Thanks.

[Simonr]

Hi William,

This questions answer depends very much on how your network is set up. As for the example you are referring to, if lightbulb 3 receives the messages at the exact same time and with roughly the same signal strength, lightbulb 3 will not be able to register any of them as it will be registered as noise when they collude. However the other mesh nodes in the network will pick up the signals, and mesh nodes have a retransmit function, so they will in turn, with random delays retransmit the signal and eventually Light bulb 3 will get both messages. If there is no firmware reprecussions taken to messages coming right after one another both messages will therefore reach Light bulb 3 eventually, in a random order, because of the random delays in the retransmits.

If there are taken firmware reprecussions in such a light switch network that says that if two signals are received within x amount of ms, only trigger the first on the first message received. Also if the two switches have different signal strength, Light bulb 3 will only register the one with the strongest signal.

So your answer will ultimately depend on your mesh network. In a basic mesh network both messages will be received through retransmits from the other nodes. Which one comes first will be random due to the random delays the nodes apply during retransmits. I hope this was of help.

NOTE: The chance of a node receiving two signals at the exact same time, is extremely miniscule, and will virtually never happen.

Best regards,

Simon

[William Nguyen]

Thank you so much! Your answer is very helpful.