Chapter 14. Precision Time Protocol - Lenovo RackSwitch G8264 Application Manual

Chapter 14. Precision Time Protocol

© Copyright Lenovo 2016
As defined in the IEEE 1588‐2008 standard, Precision Time Protocol (PTP) is a
precision clock synchronization protocol for networked measurement and control
systems. PTP provides system‐wide synchronization accuracy and precision in the
sub‐microsecond range with minimal network and local clock computing
resources. The synchronization is achieved through the exchange of messages:
General messages that carry data but need not be time stamped; Event messages
that are time stamped and are critical for clock synchronization accuracy.
A PTP network consists of PTP‐enabled devices such as switches or routers. These
devices consist of the following types of clocks:
 Master clock: In a PTP domain, the clock with the most precise time is considered
the master clock. A best master clock algorithm determines the highest quality
clock in a network.
 Ordinary clock: An ordinary clock synchronizes its time with the Master clock.
The ordinary clock has a bidirectional communication with the master clock. By
receiving synchronization/delay response and sending delay request packets,
the ordinary clock adjusts its time with the master clock.
 Boundary clock: A boundary clock connects to multiple networks. It synchro‐
nizes with the attached master clock and in turn acts as a master clock to all
attached ordinary clocks. Boundary clocks help to reduce the effect of jitter in
Ethernet‐based networks.
 Transparent clock: A transparent clock listens for PTP packets and adjusts the cor‐
rection field in the PTP event packets as they pass the PTP device.
Lenovo RackSwitch G8264 supports the configuration of ordinary clock and
transparent clock. It cannot be a master clock as the switch does not participate in
the master clock selection process.
Note: Lenovo Enterprise Network Operating System does not support IPv6 for
PTP.
By default, PTP version 2 is installed on the switch but is globally disabled. Use the
following command to globally enable PTP:
RS G8264(config)# ptp {ordinary|transparent} enable
PTP is configured on switch ports. In case of LAG ports, the PTP configuration must
be the same on all ports participating in the same LAG. The switch uses only one
port from a LAG (typically the one used by a multicast protocol) to forward PTP
packets.
By default, PTP is enabled on all the switch ports. To disable PTP on a port, use the
following commands:
RS G8264(config)# interface port <port number>
RS G8264(config­if)# no ptp
Note: PTP cannot be enabled on management ports.
Chapter 14: Precision Time Protocol
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