PTP (Precision Time Protocol) Networks are Timing/Clock hierarchies that can support multiple Master(s) and Grand-Master(s) as the source of accurate time. Each clock-node “advertises’ its capability (like clock accuracy, its source of time, it own variance etc) into the network.
These PTP networks could be Ethernet, or use IP/UDP as transport protocols or even MPLS. There are implementations and design considerations to support IEEE 1588 on Wireless links too. And then, we have DeviceNet, ControlNet and ProfiNet etc that support PTP.
As we have seen in previous articles, the PTP messages themselves could be transported in a Multicast mode or use Unicast communication, and the recent standard also supports Mixed mode (Unicast+Multicast)
All this gives various choices for the end-stations (as well as intermediate nodes) to “choose” which clock-source they want to synchronise (or syntonize) their local clock (or DPLL – Digital Phase Locked Loop) from. Although these clients are called “slaves” in the original standard, they are actually having complete choice to select a Master-Clock or Grand-Master clock.