Video Transcript
Quantum Networking (Part 4)
6m 10s
00:08
Welcome back.
00:09
Now that we’ve seen a little about how Q-SYS devices are configured,
00:13
let’s take a step back and think about the different types of network traffic.
00:17
Specifically thinking about multicast traffic.
00:20
Before Multicast, there's Unicast,
00:22
where a device is sending a packet point -to -point to another device on the network.
00:27
There’s only one destination.
00:29
There's also Broadcast – that’s when a device is sending a packet that it wants all devices in that subnet to ‘hear’.
00:37
This would have a whole subnet’s worth of receiving devices.
00:40
But, what if we only want certain devices on a network to ‘hear’ a given packet?
00:46
I have more than one intended receiver,
00:48
but I don’t want to broadcast the packet everywhere on the subnet.
00:52
That’s where ‘Multicast’ networking comes in.
00:55
This technology makes use of a virtualized IP address and MAC address range
01:00
to facilitate a dynamic flow of packets to a number of destinations.
01:05
The address range is specifically defined from 224.0.0.0 to 239.255.255.255.
01:16
The destination MAC address of a multicast stream is calculated with a special OUI,
01:22
01-00-5e so that switches and routers know to handle this as a special case.
01:30
Switches and routers with the right functionality can be configured
01:34
to make sure multicast traffic reaches only the ports that want it.
01:38
This functionality is referred to as the Internet Group Management Protocol (or IGMP).
01:45
If a given switch doesn’t support IGMP or it isn’t enabled,
01:50
then multicast traffic is effectively handled as a broadcast.
01:54
Multicast models are typically used for device discovery (such as Q-SYS device discovery)
02:01
and multi-destination media streaming that requires a lot of bandwidth.
02:05
If these media streams were broadcast, they would bog down the entire network.
02:10
Making them multicast streams helps manage the bandwidth used
02:14
and makes sure they only go to the right places.
02:18
The IGMP protocol allows devices to register for the multicast transmissions that they would like to receive.
02:25
The mechanics of this process rely on a few different aspects of the protocol.
02:30
IGMP snooping is the feature you’re enabling on the switch to provide this functionality.
02:37
This allows for the registration of groups with the switch.
02:40
An IGMP querier is then required to maintain the list
02:44
of which endpoints would like to receive which multicast streams.
02:49
Note there can only be one querier per network.
02:54
It asks each device on a regular basis what multicast groups it wants to be a part of.
03:00
The multicast routing function actually decides which stream should go to each port
03:06
based on the switch’s table of registrations.
03:09
That’s ultimately how the bandwidth is limited to only the necessary ports.
03:14
There are three versions of the IGMP protocol:
03:17
In version 1, groups can be joined, but a device can’t unregister for them.
03:24
In version 2, devices can join and leave groups.
03:28
And version 3 allows a device to register for groups only transmitted by a specific source.
03:35
Note that Q-SYS devices support IGMP V2.
03:40
Q-SYS uses a number of multicast elements to do its job.
03:44
As I mentioned before, the Q-SYS discovery protocol relies on multicast.
03:48
Instances of the Designer software and Q-SYS Cores
03:51
send multicast discovery packets in search of other Q-SYS devices.
03:56
When this discovery message is ‘heard’ by a Q-SYS device, it sends a unicast reply back to the sender.
04:02
Ever notice that you can see a device in Q-SYS configurator that’s on the wrong IP subnet in red?
04:08
This is an important observation about multicast traffic.
04:13
Since it makes use of virtualized IPs and MACs, it bends the rules a little.
04:18
Q-SYS cameras use the Web Discovery protocol for some specialized features.
04:23
The precision time protocol is also a multicast technology.
04:27
And then finally we have a number of multicast audio and video stream types…AES67 audio is one example.
04:35
AES67 streams are ALWAYS multicast.
04:38
Note that all multicast media streams must have a distinct address, or we find ourselves in trouble.
04:46
It’s kind of like duplicating an IP address on the network.
04:50
Of the multicast protocols listed,
04:53
only the multicast media streams consume much bandwidth on the network.
04:58
One question we get a lot is ‘when do I need to configure IGMP snooping?’
05:02
as it can be difficult to configure them on some infrastructures.
05:06
Q-LAN streams are unicast, so a standalone Q-SYS audio system,
05:11
even a very large one often doesn’t need any IGMP features enabled.
05:16
Here are some guidelines that will help you decide if IGMP snooping and filtering is required on your network:
05:24
Are there any 100Mbps devices on the network such as TSC7s or Audinate Ultimo devices?
05:32
These devices can tolerate much less broadcast traffic than a 1Gbps device.
05:38
Do you have multicast video on the network? IGMP is a MUST in this case.
05:45
Do you have more than 5 multicast audio streams on the network?
05:49
Remember that AES67 makes use of multicast streams for everything.
05:54
If your answers to those questions are all ‘no’
05:57
then you should be fine to leave IGMP snooping disabled on your switches.
06:02
Alright let’s take a break there, and feel free to proceed to the final video whenever you’re ready.
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Quantum Networking (Part 4)
6m 10s