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14.4 Common terms used in IEEE 1588
(source
www.nist.gov/el/isd/ieee/terms1588.cfm
)
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Boundary clock: A boundary clock is a clock with more than a single PTP
port, with each PTP port providing access to a separate PTP
communication path. Boundary clocks are used to eliminate fluctuations
produced by routers and similar network elements.
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Clock: A device providing a measurement of the passage of time since a
defined epoch. There are two types of clocks in 1588: boundary clocks and
ordinary clocks.
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Direct communication: The communication of PTP information between
two PTP clocks with no intervening boundary clock is termed a direct
communication.
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External synchronization: It is often desirable to synchronize a single
clock to an external source of time, for example to a GPS system to
establish a UTC time base. This synchronization is accomplished by means
other than those specified by 1588 and is referred to as external
synchronization.
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Grandmaster clock: Within a collection of 1588 clocks, one clock, the
grandmaster clock, serves as the primary source of time to which all others
are ultimately synchronized.
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Master clock: A system of 1588 clocks may be segmented into regions
separated by boundary clocks. Within each region, there is a single clock,
the master clock, serving as the primary source of time. These master
clocks turn synchronize to other master clocks and ultimately to the
grandmaster clock.
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Ordinary clock: An ordinary clock is a 1588 clock with a single PTP port.
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Preferred master clock set: 1588 allows for the definition of a set of clocks
that are favored over those not so designated in the selection of the
grandmaster clock.
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PTP: PTP is an acronym for P recision T ime P rotocol, the name used in
the standard for the protocol.
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PTP domain: A PTP domain is a collection of one or more PTP
subdomains. A subdomain is a logical grouping of 1588 clocks that
synchronize to each other using the PTP protocol, but that are not
necessarily synchronized to PTP clocks in another PTP subdomain.
Subdomains provide a way of implementing disjoint sets of clocks, sharing
a common network, but maintaining independent synchronization within
each set.
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PTP message: There are five designated messages types defined by
1588: Sync, Delay_Req, Follow
-
up, Delay_Resp, and Management.
Multicast communication: 1588 requires that PTP messages be
communicated via a multicast. In this style of communication, any node
may post a message and all nodes in the same segment of a subdomain
receive this message. Boundary clocks define the segments within a
subdomain.
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