48 Rockwell Automation Publication 1756-UM542A-EN-P - September 2014
Glossary
Grandmaster (GM) Within a domain, a clock that is the ultimate source of time for clock
synchronization by using the CIP sync protocol.
Local Clock The clock on a device.
Master Clock (M) In the context of a single CIP sync communication path, a clock that is the source
of
time to which all other clocks on that path synchronize on a local subnet.
Network Time Protocol (NTP) A protocol for synchronizing the clocks of computer systems over packet-
sw
itched, variable-latency data networks.
Priorities (P1 and P2) Parameters that can override the best master clock algorithm to choose a different
Grand
master.
Precision Time Protocol (PTP) The PTP protocol is a time-transfer protocol defined in the CIP sync IEEE
1588-2008
standard that allows precise synchronization of networks.
Slave Clock A clock that synchronizes its local clock to a master time.
Sequence of Events (SOE) Sequence of events is any events that need to be compared against a second event.
Synchronized Clocks Two clocks are synchronized to a specified uncertainty if they have the same
ep
och and their measurements of the time of a single event at an arbitrary time
differ by no more than that uncertainty.
System Time The absolute time value as defined by CIP sync in the context of a distributed
t
ime system where all devices have a local clock that is synchronized with a
common master clock. System time is a 64-bit integer value in units of
nanoseconds or microseconds with a value of 0 corresponding to an epoch of
January 1, 1970.
Time Sync Object The time sync object provides a Common Industrial Protocol (CIP) interface to
t
he IEEE 1588 (IEC 61588) standard for a precision clock synchronization
protocol for networked measurement and control systems. This information can
be collected to be used in diagnostics.
Transparent Clocks A device that measures the time taken for a PTP event message to transit the
de
vice and provides this information to clocks receiving this PTP event message.
Coordinated Universal Time (UTC) The time standard for 'civil time' that is time at the Prime Meridian (0 degrees
lo
ngitude). The time does not include time zone or Daylight Saving Time offsets.
System time is the same as UTC.
WallClockTime ( WCT ) WallClockTime is the time of the controller based on UTC system time.
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