The sACN (streaming ACN) protocol is supported in Artistic Licence ethernet products. The differences between Art-Net and sACN lead to some minor clashes which this document seeks to clarify.
In Art-Net, universes are called Port-Address and number from 0 to 32,767. There are 32,768 unique numbers.
In sACN, universes number from 1 to 63,999. There are 64,000 unique numbers. The standard reserves the values of 0 and 64,000 to 65,535 for future expansion.
Clearly there is the potential for confusion over the number ‘0’. If a universe is set to ‘0’ and the sACN protocol is selected, Artistic Licence products will use a universe value of ‘1’ instead.
Merging and arbitration
The sACN protocol uses a concept called Component Identifier (CID) as a method to optionally distinguish unique streams of data, and a concept called Priority as a method to define the priority of a stream.
The following table defines how sACN packets A & B are arbitrated or merged when directed to same universe.
Art-Net allows and supports multiple controllers on a network. When there are multiple controllers, Nodes will receive ArtPolls from different controllers which may contain conflicting diagnostics requirements. This is resolved as follows:
- If any controller requests diagnostics, the node will send diagnostics. (ArtPoll->Flags->2).
- If there are multiple controllers requesting diagnostics, diagnostics shall be broadcast. (Ignore ArtPoll->Flags->3).
- The lowest minimum value of Priority shall be used. (Ignore ArtPoll->Priority).