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2
AVB Networking
2.3
How Does AVB Work?
StudioLive™ Series III
AVB Networking Guide
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Guaranteed bandwidth. AVB networks intelligently manage the data traffic
giving priority to AVB data. This means standard network traffic, such as Internet
streaming, won’t prevent your audio from being delivered reliably and on time.
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Integrated clock signal. In a digital audio system with multiple devices, having
a master clock is critical to maintaining audio fidelity. The AVB specification
defines such a clock to be accurately distributed to all devices in the system.
2.3
How Does AVB Work?
On the simplest level, AVB works by reserving a portion of the available
Ethernet bandwidth for its own traffic. Because packets of AVB data are
sent regularly in allocated slots within the reserved bandwidth, there are
no interruptions or interference, making AVB extremely reliable.
What makes AVB ideal for audio networking is that it splits network traffic into
real-time traffic and everything else. All real-time traffic is transmitted on an
8 kHz pulse. Anything that’s not real-time traffic is then transmitted around
that pulse. Every 125 µs, all real-time streams send their data. Other packets
are transmitted when there is no more real-time data ready to be transmitted.
To make sure that there is enough bandwidth available for all prioritized real-
time traffic, the Stream Reservation Protocol (SRP, IEEE 802.1Qat) is used.
Every AVB compliant switch between each talker and listener will then make
sure sufficient bandwidth is available using SRP, making it a foundational
building block of the AVB standard. Every switch and AVB device on the
network must implement SRP and send real-time traffic at the 8 kHz pulse. If
one of the devices on the network does not employ this standard, then real-
time traffic could be potentially delayed, causing jitter in the output.
2.4
AVB Hardware Components
In an AVB network, every device to and from which audio is flowing must
adhere to the AVB standard. These devices consist of the following types:
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AVB Talkers. These devices act as the source for an AVB
stream, sending out audio onto the network.
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AVB Listeners. These devices are the destinations
for the streams sent out by the Talkers.
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AVB Switches. This is the network hub to which every Talker and
Listener must be connected. At its most basic level, an AVB Switch
analyzes and prioritizes traffic on the network. It should be noted
that just like there can be multiple talkers and listeners on the
same AVB network, there can also be multiple AVB Switches.
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AVB Controllers. A controller can be a talker, a listener, or neither. These devices
handle routing, clock, and other settings for AVB devices using AVDECC.
The most important rule to keep in mind when setting up an AVB network is
that the talker (device sending audio) and listener (device receiving audio) must
be connected to an AVB-compatible switch. All the AVB devices on the network
must share a virtual clock that defines when the AVB packet should be played.
As previously mentioned, devices communicate on an AVB network as
“talkers” and “listeners.” An AVB talker transmits one or more audio streams
to the network. AVB listeners receive one or more of these streams from the
network. It should be noted that an AVB device, like the StudioLive Series
III mixers and NSB-series stage boxes, can be both a talker and a listener.
For example, StudioLive 32 can simultaneously “Talk” (send channels out
to the network) and “Listen” (receive channels from the network).
AVB devices stay in sync by selecting the best master PTP clock after the
devices connect with one another. This ensures that every AVB device on the
network will maintain precise timing, which is critical to audio quality.
