Answer

If you are experiencing packet loss on NVX AES67 streams where the Q-SYS Core is the PTPv2 Grandmaster, one common cause is the network topology. Specifically, check if the stream is traversing a Layer 3 path without a boundary clock. This scenario often leads to PTPv2 timing failures, which can disrupt AES67 audio streams.

The root issue is related to Time-To-Live (TTL) settings on multicast packets. NVX devices typically use a TTL value of 1 for PTP packets, meaning these packets cannot survive traversal through a router to another subnet. As a result, clock synchronization fails when the devices are separated by Layer 3 routing without proper boundary clocks. 

For more information regarding NVX devices, see Crestron Documentation. 

TTL or Time To Live determines how how long a packet lives on a network before it discard or refreshed. In Q-SYS, AES67 is set to 10. So, after 10 switch hops, an AES67 packet is discarded to prevent it from circling the network indefinitely. This is not a user-changeable setting in Q-SYS Designer Software or Q-SYS Core Manager. See the Network > Multicast topic in Q-SYS Help for more information.

Recommended Action

• Check if your NVX AES67 streams are crossing Layer 3 boundaries.
  • If so, ensure boundary clocks are present in the network design and keep NVX traffic within a single subnet when possible.
• For detailed guidance, please refer to Crestron documentation.