Ideally you determine whether a device is still on the network through the normal use of QUEUED_MESSAGES so that you routinely pick up the Queued messages and any Status messages that are pending.
The reason the STATUS_MESSAGE with STATUS_NONE exists as there were some that had a need/desire to be able to routinely determine if a device is online but didn't necessarily have the ability or desire to be handling the Queued/Status messages coming back. So we defined a specific way for people that want to do that.
My personal position is that ANY message that generates a response, even a NACK, lets you know the device is online. Ideally you should be using the normal QUEUED_MESSAGES poll so that you are getting that info back and the STATUS_NONE mechanism is only for those rare exception cases.
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Scott M. Blair
RDM Protocol Forums Admin
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