Dante: When do I HAVE TO use multicast?
Welcome to the second part about Dante Multicast! After we still had the choice in the first part ("When should I use multicast?") whether we use multicast or prefer to stick with unicast, there are also situations in which we have no choice and multicast is almost imposed.
This is always the case when we need more flows on the output side than the device can provide. Unfortunately, this information is usually difficult or impossible to find in marketing brochures. Accordingly, the surprise is great when you are advised of your limit in the Dante Controller. Fortunately, thanks to multicast, there is a way out for many situations.
Before we dive into the practical examples, here is the crucial table with the number of possible flows. This depends primarily on the Audinate Dante chip used. The device manufacturer therefore has no direct influence on the approved flows, but selects a Dante chip that he believes is suitable for his device.
| Dante Chip | Link | max. Kanäle | max. Flows | min. Latenz |
| Ultimo | 100 MBit/s | 4 in / 4 out | 2 in / 2 out | 1 ms |
| Broadway | 1 GBit/s | 16 in / 16 out | 16 in / 16 out | 0.25 ms |
| Brooklyn II | 1 GBit/s | 64 in / 64 out | 32 in / 32 out | 0.25 ms |
| HC | 1 GBit/s | 512 in / 512 out | 128 in / 128 out | <1 ms |
Let's take a look at two typical examples that often occur in larger Dante systems:
Example 1: 2-channel adapter
The small Dante AVIO adapters have proven themselves on stage for mobile purposes. Thanks to PoE, they are quickly ready for use without a power supply and usually deliver two inputs or two outputs very reliably, or both in the case of my AVIO AES / EBU adapter *. A similar function can be found in this Neutrik adapter * with a somewhat more robust housing.
Most of these 2-channel Dante adapters have a maximum number of only two output flows. If you just want to route the signal to the mixer, you will never notice this limit.
However, if you want to use such an adapter to distribute an audio signal to more than two devices, the Dante Controller will kindly inform you of the flow restriction: “No more flows (TX), transmitter cannot support any more flows” .
This situation occurs, for example, if you want to feed several Dante speakers or power amplifiers with the 2-channel adapter. But even in normal stage use, the limit of 2 flows is reached if the signal is to be routed in parallel to the FOH mixer, to the monitor mixer and perhaps also to a recording PC.
Now, if you're wondering how many flows your devices support, there's an easy way to find out. In the Dante Controller, the currently occupied and all possible transmit flows are displayed on the transmit page of the device view.
We currently see two unicast flows in use there because I have already routed the signal to two devices. The “total 2 of 2” indicates that the device supports a maximum of two flows and both have already been exhausted and no further flows can be created.
Solution: multicast
The remedy in such a situation is to create a multicast flow, as we have already seen in the first multicast part. One click on the multicast button, select the two channels, and confirm with a click on the “Create” button, and our little Dante adapter transmits its channels as multicast.
Existing unicast routings for these channels are automatically converted to multicast. As a result, the two unicast flows now become just one multicast flow. It is thus possible to feed other Dante receivers with this signal.
Example 2: 64-channel DSP
There can be limits not only with the cheap Dante converters. Even with the large DSPs with their 64 inputs and outputs promised by marketing, you sometimes come across the flow limitation. And since almost all DSPs with this number of channels use the Brooklyn-II Dante chip, they all have this limitation in common: a maximum of 32 flows.
In many situations you can live with this limit. Most Dante devices require more than one audio channel anyway. For example, it is possible to route the 64 output channels from the DSP to 32 power amplifiers, i.e. always two channels per flow, as is usually the case with stereo power amplifiers.
If, on the other hand, you don't use multi-channel power amplifiers but use Dante speakers, this plan no longer works. With unicast flows, each speaker needs its own flow. And suddenly a DSP only has enough flows to supply 32 loudspeakers.
The use of multicast is not immediately obvious, because every loudspeaker should get its own signal. Finally, we bought a DSP with 64 channels so that we could mix and level its individual signal for each loudspeaker.
Solution: multicast
Nonetheless, switching from unicast to multicast is effective here. The number of flows required can be reduced by combining several channels in one flow. If we create a lot of 4-channel multicast flows, we need just 16 flows for our 64 output channels, or 10 flows for the 40 loudspeakers in the example.
With 64 audio channels, however, we are already approaching a bandwidth of 100 Mbit/s. If we send this to the network as a multicast, every loudspeaker receives all the traffic. Many loudspeakers have the Ultimo Dante chip built in because they actually only need one Dante channel. However, the Ultimo chip only has one 100Mbit port. Such a multicast application only works in conjunction with IGMP snooping so that no packets are lost.
The switches listen to the data packets and try to determine which recipient needs the multicast streams. Accordingly, the packets are no longer distributed to all devices, but only to those that have subscribed to this stream. The multicast load can increase to over 100MBit without overloading the individual loudspeaker.
Granted, it's not often that we connect more than 32 devices to a DSP. But if you do, you are ready now!
* Affiliate link
More articles on Dante: