# Linking

The linking is used to to relay the message via so called linking nodes. All S2 nodes offer this functionality. A linking node can be a node with no sensor or any measuring node in a given radio network.

The linking is based on the mechanism shown below using the ID Info header field described in [Header](/s2-radio-system-manual/s2-system-description/s2-node/s2-communication-protocol/frame/header.md).

<figure><img src="/files/QcXRhTLvmpWozAxXxB61" alt=""><figcaption></figcaption></figure>

When the ID Info high nibble is equal to low the message has reached the final destination in outgoing message and the command is to be handled by the node.

The answer has reached the addressed PC node when the the ID Info low nibble is equal 0 and the message shall be then routed to UART.


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