Precision time protocol (commonly abbreviated as PTP) is a protocol designed to synchronize real-time clocks in the nodes of a distributed system that communicate using a network. On a local network, PTP can commonly achieve sub-microsecond accuracy. It is standardized as IEEE 1588.
The nodes in the PTP network (referred to as clocks) are organized into a leader-follower hierarchy (formerly referred to as "master-follower" hierarchy). Followers synchronize to their leaders, which in turn can be followers to other leaders. The leader-follower relationship is determined by running on each clock, a so-called Best Leader Clock (BMC) algorithm. By determining the relationships in the network dynamically, the PTP network can resolve cycles and prune the general interconnect graph down to a tree of leaders and followers.
The root of this tree (the grandmaster) is the ultimate leader that all clocks (possibly indirectly) synchronize to. Typically, its time would in turn be synchronized by GPS.
Interior nodes in this network are called boundary clocks (BC). They have one follower port (leading to a leader) and one or more leader ports (leading to follower clocks).
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