Precision Time Protocol

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Precision Time Protocol

Communication protocol
Abbreviation	PTP
Purpose	Time
Developer	IEEE
Introduction	2002;24 years ago (2002)
Ports	udp/319, udp/320

The Precision Time Protocol (PTP) is a protocol for clock synchronization throughout a computer network with relatively high precision as compared to using the earlier developed Network Time Protocol (NTP) and therefore potentially higher accuracy depending on the configuration. In a local area network (LAN), accuracy can be sub-microsecond IEEE1588-2002) IPv4 multicast address
( –A universally unique numeric identifier for the clock. This is typically constructed based on a device's MAC address.

Quality –A clock's estimate of its stability based on observation of its performance against the PTP reference.

IEEE 1588-2008 uses a hierarchical selection algorithm based on the following properties, in the indicated order:

1. Priority 1 –precision between clock and UTC, in nanoseconds (ns)
2. Variance –MAC address-based selection is used as a tiebreaker when all other properties are equal.

IEEE 1588-2002 uses a selection algorithm based on similar properties.

Clock properties are advertised in IEEE 1588-2002 Sync messages and in IEEE 1588-2008 Announce messages. The current leader transmits this information at regular interval. A clock that considers itself a better leader will transmit this information in order to invoke a change of leader. Once the current leader recognizes the better clock, the current leader stops transmitting Sync messages and associated clock properties (Announce messages in the case of IEEE 1588-2008) and the better clock takes over as leader. The BMCA only considers the self-declared quality of clocks and does not take network link quality into consideration.

Via BMCA, PTP selects a source of time for an IEEE 1588 domain and for each network segment in the domain.

Clocks determine the offset between themselves and their leader. Let the variable t {\displaystyle t} is defined by: