Precision Time Protocol (PTP) is a protocol used to synchronise clocks throughout a computer network. On a  Local Area Network, it achieves clock accuracy in the sub-microsecond range.

The naming convention is changing as previous terminology is considered to be inappropriate so we will refer to Leaders and Followers rather than Masters and Slaves.

PTP is employed to synchronise networks that require precise timing but lack access to satellite navigation signals, although clock may be derived from a GPS source. An ordinary clock is a device with a single network connection and is either the source or destination for a synchronization reference. A boundary clock has multiple network connections and can accurately synchronise one network segment to another¹.

In a DANTE domain, devices lock either directly or indirectly to one single Leader device. This ensures that audio packets are delivered in the correct place, at the correct time. When clock drifts, the audio is muted. Clock can be generated by various means and some sources are more accurate and reliable than others.

Single subnet

Within a single subnet, the standard DANTE method of multicast PTP clocking, version 1 is used.

One Leader device is automatically elected or manually specified. This device broadcasts the clock signal via multicast PTP, and all other devices follow their own clocks to the Leader device.

Multiple subnets

In domains that span more than one subnet, a Leader is automatically elected (or is manually specified) for the domain, and one “boundary clock” device will be automatically assigned for each subnet. Usually the Leader will act as the boundary clock in its own subnet.

The Leader transmits the PTP clock signal via multicast to the follower devices in its own subnet, as is the case for single subnets. The elected boundary clock transmits the clock signal via Unicast PTP, through the router to the boundary clock in the adjoining subnet which in turn transmits multicast PTP to the other devices in the subnet.

DANTE uses a Best Leader Clock Algorithm to elect the Leader. The “election” can be rigged by selecting a device as the preferred leader. A device which is set to synch to an external clock will win the election, where the external clock is more accurate than the internal clock of the device in the domain.

DANTE Domain Manager takes care of clocking automatically.

Sources

^{1 https://en.wikipedia.org/wiki/Precision_Time_Protocol}

^{2 https://www.audinate.com}