Audio Networking: An Introduction To Another Important Piece Of The Puzzle

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Tagging is mostly used for carrying multiple VLANs between switches and other pieces of network infrastructure. Because only one VLAN can be untagged to each port, tagged VLAN interfaces are required when multiple VLANs need to traverse the same interface.

The most common example of this is when there are two switches connected to each other. Let’s say we have a Dante, Control network, and dSnake VLAN on front of house (FOH) and back of house (BOH) switches, and we have one Cat-6 cable run between them on port 24 of both switches. Each of these VLANs will be tagged on interface 24 of both switches.

This way, the switches know that the data is allowed to traverse that interface, but it’s not removing or adding the VLAN identification to the data. It’s simply allowing the data to pass through while keeping it’s unique VLAN identification so the switch on the other side can allow that data to access devices on its untagged interfaces.

How It Really Works

Here’s where we go back to the VLAN ID being a 12-bit segment of the ethernet frame. Let’s say you have a wireless microphone receiver with Dante plugged into port 16 of your switch, which is untagged on VLAN 21. When Ethernet frames enter added to the frame. This tells the switch how to handle that frame and where it’s allowed to go. Right now, it’s allowed to go to any interface that’s untagged VLAN 21.

Let’s say you have a mixing console with a Dante interface connected to port 17 of the switch and untagged on VLAN 21. When the Ethernet frame from the wireless microphone receiver is traveling to the console, it’s sent out of the network switch where the switch removes the VLAN ID to make that frame accessible by the console.

So far, we have one switch with three isolated VLANs – one for staff network, one for AV control, and one for Dante. Let’s say we have another switch backstage where there are also some snakes and amplifiers that use Dante, and some devices such as DSPs and projectors that need to be on the AV control network. They need access to the FOH switch, and there’s a Cat-6 cable connecting both switches. Just like the FOH switch, we need to untag the VLANs to the access ports. This time, the big change in the configuration is that we need to extend the VLANs across the two switches. Here comes uplink!

If we had three uplink cables — one for each VLAN — it would be as simple as untagging the correct VLAN to the correct uplink and patching it into the other switch, but we only have one line. Luckily, we’ve got tagging. As mentioned before, tagging a VLAN to a switch port allows the ethernet frame to traverse that port.

In this case, we can tag VLANs 10, 20, and 21 on port 24 on both switches, plug them into each other, and now there are three separate networks using a single set of switches with a single uplink cable. So now we have a network consisting of three separate networks using two switches and uplink cabling. Pretty cool, eh?

Upgrade Time

One of my favorite things about networking in AVL systems is how much it can simplify future additions. Let’s say down the road you end up with an Allen & Heath console and dSnake. You’re still running your staff, AV control, and Dante networks, but you also need to add the new dSnake. If it’s Layer 2 or above on the OSI model, it can traverse network switches and should be happy living in a VLAN.

So let’s add VLAN 22 to both switches. Tag it to the uplink port on each switch, untag it to the port going to the dSnake interface at FOH and the dSnake interface backstage. Provided everything else is set up correctly, there is now connectivity!

VLANs can seem complicated at first, but they’re a pretty fundamental piece to networking. When used correctly, they can help in creating some great solutions to building efficient AVL system networks.