Art-Net and sACN

Art-Net I, written in 1998, sent all of its data as broadcast, which reaches every device on the network. Art-Net II (2006) moved mostly to unicast, and Art-Net 3 (2011) prohibited broadcasting DMX data: a controller discovers the nodes with ArtPoll messages and then sends each universe by unicast only to the nodes subscribed to it. Art-Net 3 also raised the address space to 15 bits, or 32,768 universes, and Art-Net 4, released in 2016, keeps the unicast rule. Equipment built to Art-Net I still depends on broadcast.

sACN normally uses multicast. Each universe has its own multicast group in the 239.255 range, on UDP port 5568, and a receiver joins only the groups of the universes it uses. E1.31 also allows unicast, in which case the receiver addresses are entered on the source. Each source carries a priority from 0 to 200, 100 by default, and a receiver that gets the same universe from several sources follows the highest priority, which lets a backup console take over. Since the 2016 revision, sources also send universe discovery packets listing the universes they transmit.

On a large system, multicast sACN on managed switches with IGMP snooping, or unicast Art-Net, delivers each universe only where it is needed. Broadcast traffic grows with every universe and reaches every device, and at scale it can saturate links and node processors, causing lag or lost data. Lighting networks are usually planned universe by universe and kept apart from other traffic.