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  • Case ID: 338101
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Relay Configuration and implementation in BLE mesh network

Jeena Francis

I am trying to implement the following: I have a mesh node built using the Sensor Server  example for publishing temperature data. I want one relay node to transmit the temperature data to another node, which is not within the radio range of the first node. This second node is built using the Sensor Client model. My question is: how do I implement the relay feature, which code should I use for that, and what changes need to be made?

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  • 0

    Hi Jeena, 

    By default most of mesh sample has the relay feature enable. You don't have to do anything except from having CONFIG_BT_MESH_RELAY=y (by default in many samples)

    If you don't want to have relay feature enabled, just set CONFIG_BT_MESH_RELAY=n in prj.conf

  • 0 in reply to Hung Bui

    Do I need to make any changes in the BLE Mesh app?

  • 0 in reply to Hung Bui

    I already connected to a mesh node and CONFIG_BT_MESH_RELAY=y is in the code 

  • 0 in reply to Jeena Francis

    Hi Jeena, 
    Please make sure it's still connected. When it's connected you should see the button say "Disconnect" not "Connect". Also you would need to load the role (read the configuration server) by pulling the screen downward (touch and pull down) 
    The screen should look like this: 

  • 0 in reply to Hung Bui

    Relay enabled successfully.
    I have one Sensor Server node that publishes data to a group address, and one Relay node flashed with Sensor Client code. The Relay node is enabled as a relay in the application and is configured to publish and subscribe to the same group address. The last node is a Client node, also flashed with Sensor Client code and subscribed to the same group address used by both the Server and Relay nodes. However, the messages are not received by the Client node. The Relay node is placed between the nodes, but the messages are still not reaching the Client.
    what changes need to be done for proper working.

  • 0 in reply to Jeena Francis

    Hi Jeena, I'll take over this case for a bit as Hung is OOO currently.

    First of all, that sounds like it 'should' be working, though the thing with Mesh or any "flooding network" is that it might require some tweaking to get working perfectly. If for instance the Sensor Client is just within reach of the relaying node, and not the other, and the SC node is not scanning with the radio that exact moment it needs to, then it will miss this message. With Mesh you could counter this by eg. increasing the publish retransmission count, or get more nodes within the range of the one you need to reach, or send a message that you want the receiving node to acknowledge, so that you know that it has been recieved. With a small test with 3 nodes, it looks like this is so simple that it should immediately work, though the simplicity of the set-up could ironically be the issue. You for instance would typically like a Mesh node to be within the range of a few others, not just one, to counteract this.

    Though with that out of the way, I agree that what you have tried here should work the majority of the time. Does it always fail? Could you try increasing publish retransmission count? Make sure the TTL is high enough, the way TTL works can be a bit confusing (0 and 1 means the same etc.).

    Regards,

    Elfving

  • 0 in reply to Elfving

    For my sensor server TTL value 2,Relay Node- 3 and client node- 4
    in relay node retransmit count 3,intervel 120ms.

    As mentioned above, if the publish retransmission count is increased, on which node should it be increased? It will be disabled on all three nodes.

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  • 0 in reply to Jeena Francis

    I'm not sure if I understand. 

    Jeena Francis said:
    For my sensor server TTL value 2,Relay Node- 3 and client node- 4

    So in a situation where only the sensor server sends anything, then the TTL value that is being sent from this node is the only thing that matters. The message will be sent with TTL = x in the first node, then the TTL will decrease by one after each hop. The relaying node will relay the message forward with a TTL of x-1. Though the confusing thing with TTL is that both 0 and 1 means the same thing practically (it not being relayed). 

    So I am not sure why you want increasing values of TTL on the different nodes? And a TTL of 2 in the sensor server node is the absolute minimum you could use, just to not have that as a potential issue it might be an idea to increase it further.

    Jeena Francis said:
    in relay node retransmit count 3,intervel 120ms.

    Sounds good.

    Jeena Francis said:
    As mentioned above, if the publish retransmission count is increased, on which node should it be increased? It will be disabled on all three nodes.

    The main node and the relaying node would benefit from this, but if only the final node is not receiving the message maybe the relaying one should be the focus.

    Would it be possible to bring the final node into the range of the one sending, just to make sure that the problem isn't related to anything else?

    Regards,

    Elfving

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