**Mandatory.** Must be implemented by all level I and level II devices.

This event can be used as a fast way to find out which nodes there is on a segment. All nodes receiving it should respond. 

 | Data byte | Description | 
 | :---------: | ----------- | 
 | 0 | Node-ID or 0xFF for all nodes. | 

Response for a Level I node is [CLASS1.PROTOCOL, Type=32 (Who is there response)](./class1.prototocol.md#type32).
    
A Level II node respond with [CLASS2.PROTOCOL, Type=32 (Level II who is response)](./class2.protocol.md#type32) to this event.
