ClearOne Digital Media - Manual (Page 15)

pg 15 StreamNet Digital Media and System Design Reference Guide
How audio and video signals stay in sync with AVB.
An 802.1AS network timing domain is formed when all devices follow the requirements of
the 802.1AS standard and communicate with each other using the IEEE 802.1AS protocol.
Within the timing domain there is a single device that provides a master timing signal called
the “Grand Master Clock”. All other devices synchronize their clocks with this master.
The device acting as Grand Master may be auto selected or specifically assigned. Example:
If the network is used in a professional environment that needs “house clock” for audio, or
“genlock” for video. Or if a specific timing hierarchy is needed for other reasons.
AVB devices typically exchange capability information after physical link establishment. If
peer devices on a link are network synchronization capable they will start to exchange clock
synchronization frames. If not, then an AVB timing domain boundary is determined.
Traffic shaping is yet another way AVB ensures tight timing and synchronization of signals
is achieved. Traffic shaping is the process of smoothing out the traffic for a stream so the
packets making up the stream are evenly distributed in time. If traffic shaping is not done
at sources and bridges, then the packets tend to “bunch-up” into bursts of traffic that may
overwhelm buffers in subsequent bridges, switches or other network infrastructure devices.
The AVB architecture implements traffic shaping using existing 802.1Q forwarding and
priority mechanisms and also defines a particular relationship between priority tags and
frame forwarding behavior at endpoints and bridges.
The vision of AVB is to realize a standard that will allow “no-compromise” streaming of
AV signals over modern networks. Since the same could be said of StreamNet products,
you may look to ClearOne to take a leadership position with respect to implementing AVB
support across our line.
Common AV Signals and Interfaces