Stream Configuration - Ravenna AES67 Practical Manual

permanent offset from master without necessarily affecting the synchronization stability.
The node may settle into a synchronized condition, but most likely larger latency settings will
be required for streams coming from/going to this node due to a permanent displacement
between local and network time. It is good advice to only use GbE switches in the network
and connect end nodes with FE interfaces directly to the GbE switch ports.
•
PTP-aware switches: as mentioned earlier, PTP-aware switches are certainly valuable (or
even required) to improve synchronization (especially in larger networks), but they may make
things more complicated and require deeper knowledge for proper configuration. Check if
PTP-aware switches are part of your network and try switching PTP support off (temporarily).
Make sure that all configuration requirements for COTS switches are in place (i.e. QoS, IGMP
etc.).
2.4

Stream configuration

Once your network is prepared as described above, you are ready to configure streams. While AES67
calls for support of multicast and unicast transport, we will focus on multicast streaming only as this
is the method commonly available on all AES67 devices. Configuring and connecting to multicast
streams almost always follows these two basic steps:
1. Configure and start a multicast stream on the sender node
2. Make the related SDP data available to the desired receiving node
3. Connect to the selected stream
Execution of these steps usually varies between individual devices; in this guide we use screenshots
from the RAVENNA Virtual Sound Card (RVSC) which is based on the RAVENNA framework
developed by ALC NetworX. Consult the respective Operating Manuals of other devices to execute
these steps accordingly.
2.4.1 AES67 stream format
Since the main focus of AES67 is on interoperability, the stream format variations to be supported by
all devices are pretty narrow:
•
Sample rate: 48 kHz
•
Data encoding: linear PCM with 16- and 24-bit (L16 / L24)
•
Number of channels per stream: 1..8
•
Packet time (number of samples per packet): 1 ms (48 samples per channel per packet)
Other variations are recommended, but not required to be supported. Therefore, we focus on a
typical AES67 stream setup: a stereo stream with L24 encoding running at 48 kHz with 1ms packet
time.
2.4.2 Creating an AES67 stream
Invoke the stream creation function ("create Tx stream", "create session source" or alike) and fill in
the parameters as required:
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AES67 Practical Guide