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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.
Universe numbering
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.
CID
Priority
What happens?
A=B
A=B
Streams A and B are identical and are output as DMX.
A<>B
A=B
Streams A and B are from different controllers but have same priority. The streams will be merged using the LTP/HTP settings of the product. A maximum of two streams can be merged. If a third stream appears it will be ignored.
A=B
A>B
Streams A and B are from the same controller and A has higher priority. B is ignored and A is output. If A stream stops for more than a 5 second time out period, the lower priority stream will take over. If a stream with a higher priority that which is outputting is detected, the higher priority stream immediately takes precedence.
A=B
A<B
Streams A and B are from the same controller and B has higher priority. A is ignored and B is output. If A stream stops for more than a 5 second time out period, the lower priority stream will take over. If a stream with a higher priority that which is outputting is detected, the higher priority stream immediately takes precedence.
A<>B
A>B
Streams A and B are from different controllers and A has higher priority. B is ignored and A is output. If A stream stops for more than a 5 second time out period, the lower priority stream will take over. If a stream with a higher priority that which is outputting is detected, the higher priority stream immediately takes precedence.
A<>B
A<B
Streams A and B are from different controllers and B has higher priority. A is ignored and B is output. If A stream stops for more than a 5 second time out period, the lower priority stream will take over. If a stream with a higher priority that which is outputting is detected, the higher priority stream immediately takes precedence.
Numerous of the Art-Net packets contain Version numbers.
These can be either the version number of Art-Net or the Node’s version number. The terms ProtVerHi / ProtVerLo are used to describe the Art-Net protocol version number. This has never been changed and is set at:
ProtVerHi = 0
ProtVerLo = 14
The terms VersInfoH / VersInfoL are used to describe the Node’s version number. This field is defined by the manufacturer and usually contains the firmware revision number. The ArtPollReply message contains this information.
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).
A Node must respond to an ArtPoll with an ArtPollReply within 3 seconds. If the Controller does not receive a response in this time it should consider the Node to have disconnected. It is a requirement of Art-Net that all controllers broadcast an ArtPoll every 2.5 to 3 seconds. This ensures that any network devices can easily detect a disconnect.
In order to make a product visible in DMX-Workshop, the product must reply to an ArtPoll with one or more ArtPollReply. The screenshot below shows a Wire Shark capture of the ArtPollReply packets from a Data-Lynx IOP.
Common errors in formatting ArtPollReply are:
1) The text signature at the top of the packet is “Art-Net”. It is case sensitive.
2) DMX-Workshop only listens on Port 6454 (decimal).
If you have difficulty making your product visible in DMX-Workshop then submit a Wire Shark capture on a support ticket and we will try to help.
DMX-Workshop is our free-of-charge Windows application for monitoring and configuring Art-Net devices. The software requires Administrator permission to run. The installer for DMX-Workshop will attempt to auto-enable this for you, but it may fail depending on the configuration of your PC and your security settings.
To achieve manually, right-click the DMX-Workshop icon and select ‘run as administrator’. The right-click menu also accesses the properties dialogue which allows you to select DMX-Workshop to always run as administrator.
There are three methods for finding the IP address of an Art-Net product:
Connect using DMX-Workshop, this will display the product in a network list along with its IP address. DMX-Workshop can be downloaded from here.
Ping: Open a command line window and use the ping command. If the products are on the normal Art-Net address range, type: “ping 2.255.255.255”. This approach is best on a Mac as Macs do not support net-bios.
Perform a net-bios search (Windows only). To do this, connect the product to your laptop’s network, open browser and type in the net-bios name of the product you are using (see below). Occasionally the net-bios cache in the browser gets out of date. To flush the cache and restart, type the following in the browser window: nbtstat -R