When Dante was the only AV-over-IP (AVoIP) transport on most networks, clocking took care of itself. Dante elected a grandmaster, the devices synchronized, and engineers moved on. Few designs gave the clock any more thought than that.
Those early days of AVoIP are behind us. It is now a mature technology that every domain of AV leverages. That set it and forget it approach from those simple Dante deployments worked when an AV network mostly lived inside one ecosystem. It becomes more dangerous when several media platforms and clock domains share the same network. Today’s AV networks may carry Q-SYS, Dante, AES67, NVX, IPTV, control and many other things across the same switching infrastructure. Several of those systems depend on precise PTP synchronization, and multiple devices in the same PTP domain may be capable of winning the clock election. This all gets even more complicated when all this traffic is also on the enterprise network handling the rest of the building’s networking requirements.
On a large commercial deployment in Houston, every AV device was sitting at the same PTP priority. The Q-SYS core was acting as the grandmaster, but no one had chosen it for that role. It was merely winning the election on tiebreakers. After the customer’s IT team hardened the network, the election stopped resolving to the core. The Q-SYS amps began reporting “Packet Missing” errors, then “PTP Grandmaster Mismatch”. The audio streaming failed across the system.
The customer’s IT team was doing what great IT teams do. They were improving their cybersecurity stance. The AV system had not been designed to survive that heightened stance. I had a hand in that design, both the original build several years ago and the refresh. The fix was setting the PTP priority on the Q-SYS core to 1 so the grandmaster was chosen on purpose instead of by default. In hindsight it should have been that way from the original commissioning.
Broadcast facilities treat dedicated PTP grandmasters, usually redundant, as a routine part of the ST 2110 design. Commercial AV is arriving at the same conclusion from a different direction. The clock is infrastructure and it needs to be engineered with the same discipline as the signal path it serves.