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Configuring PTP
Overview
Precision Time Protocol (PTP) synchronizes time among devices. It provides greater accuracy than
other time synchronization protocols such as NTP. It can also be used for frequency synchronization.
For more information about NTP, see "Configuring NTP."
Basic concepts
PTP profile
A PTP profile defines two PTP standards: IEEE 1588 version 2 and IEEE 802.1AS.
• IEEE 1588 version 2—1588v2 defines high-accuracy clock synchronization mechanisms. It
can be customized, enhanced, or tailored as needed. 1588v2 is the latest version.
• IEEE 802.1AS—802.1AS is introduced based on IEEE 1588. It specifies a profile for use of
IEEE 1588-2008 for time synchronization over a virtual bridged local area network (as defined
by IEEE 802.1Q). The BMC algorithm in 802.1AS supports only the peer delay mode, and
point-to-point full-duplex Ethernet, IEEE 802.11, and IEEE 802.3 EPON links.
PTP domain
A PTP domain refers to a network that is enabled with PTP. A PTP domain has only one reference
clock called "grandmaster clock (GM)." All devices in the domain synchronize to the clock.
Clock node and PTP port
A node in a PTP domain is a clock node. A port enabled with PTP is a PTP port. PTP defines the
following three types of basic clock nodes:
• Ordinary Clock (OC)—A PTP clock with a single PTP port in a PTP domain for time
synchronization. It synchronizes time from its upstream clock node through the port. If a clock
node works as the clock source and sends synchronization time through a single PTP port to its
downstream clock node, it is also called an OC.
• Boundary Clock (BC)—A clock with more than one PTP port in a PTP domain for time
synchronization. A BC uses one of the ports to synchronize time from its upstream clock node,
and uses the other ports to synchronize time to the relevant upstream clock nodes. If a clock
node works as the clock source and synchronizes time through multiple PTP ports to its
downstream clock nodes, it is also called a BC, such as BC 1 in Figure 18.
•
Transparent Clock (TC)—A TC does not need to keep time consistency with other clock nodes.
A TC has multiple PTP ports. It only forwards PTP messages among these ports and performs
delay corrections for the messages, instead of performing time synchronization. TCs include
the following types:
{ End-to-End Transparent Clock (E2ETC)—Forwards non-P2P packets in the network and
calculates the delay of the entire link.
{ Peer-to-Peer Transparent Clock (P2PTC)—Forwards only Sync, Follow_Up, and
Announce messages, terminates other PTP messages, and calculates the delay of each
link segment.
Figure 18 sho
ws the positions of these three types of clock nodes in a PTP domain.
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