ClearOne Digital Media - Manual (Page 12)

pg 12 StreamNet Digital Media and System Design Reference Guide
Audio Video Bridging (AVB)
ClearOne is a proud member of the AVnu Alliance, an industry forum dedicated to the
advancement of professional-quality audio video transport by promoting the adoption of
the IEEE 802.1 Audio Video Bridging (AVB), and the related IEEE 1722 and IEEE 1733,
standards over various networking link-layers.
An “Audio Video Bridging” network is one that implements a set of protocols being
developed by the IEEE 802.1 Audio/Video Bridging Task Group. The four primary differences
between the Audio Video Bridging (AVB) architecture and existing 802 architectures are as
follows:
1 . Precise synchronization of audio and video signals as required by high quality AV
systems.
2 . Traffic shaping for media streams to ensure ultra low latency and signal integrity.
3 . Admission controls.
4 . Identification of non-participating devices.
Key to AVB is the fact that it has been specifically designed for AV use and addresses the
unique requirements of distributing an audio and video signal in a high quality manner over
a standard switch Ethernet network.
To understand why AVB is special, lets look at the requirements for A/V streaming.
First, it must be possible to synchronize multiple streams so they are rendered correctly in
time with respect to each other. This might be to ensure lip sync or to keep multiple digital
speakers in phase, or it could be to maintain tight time sync of 40 or more microphone
channels feeding a live mixing desk in a live sound or studio environment. Regardless of the
application, what this means is A/V streams must be synchronized to within approximately
one microsecond. Something that is impossible for a standard switched network to achieve
using regular 802 architecture.
Furthermore, applications must be able to receive a high level of confidence that the network
resources needed are available and will remain available as long as the application needs
them.
This is sometimes referred to as a “reservation”, or “admission control”. The intent is for an
application to notify the network of the requirements for a stream ahead of time, and have
the network lock down the resources needed for that stream and, if they are not available, to
notify the application so the stream may be stopped or an error message delivered.
Common AV Signals and Interfaces