Edge-Core ECS4660-28F, Руководство по управлению, Страница: 964 / 2020

C
HAPTER
24
| System Management Commands
Precision Time Protocol
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the output port, and adjusts the time stamp to compensate for
this delay. The value of the correction update and checksums
are specific to each output port and message since the residence
time are not necessarily the same for all paths through the
switch or for successive messages crossing the same path.
peer-to-peer – This method measures the delay required for
PTP event messages to cross the link from the peer port on the
upstream device to the input port on the switch, as well as the
residence time required for PTP event messages to cross from
the input port to the output port, and adjusts the time stamp to
compensate for both of these delay times.
D
EFAULT
S
ETTING
Disabled
C
OMMAND
M
ODE
Global Configuration
C
OMMAND
U
SAGE
◆
Setting the switch to boundary mode allows it to participate in the
selection of the best master clock. If no better clock is detected, it will
become the grandmaster clock within its PTP domain, and the parent
clock to all connected devices. However, if the best master clock is
found to be a another clock connected to the switch, the switch will
synchronize to that clock as its child, and then acts as the parent clock
to devices connected to other ports. After initial synchronization, the
switch and connected devices exchange timing messages to correct for
time skew caused by clock offsets and network delays.
◆
Setting the switch to end-to-end transparent mode makes it
synchronize all ports with the grand master clock connected to the
switch. The switch corrects PTP message time stamps for the delay
incurred passing through it. This option causes less jitter and error
accumulation than that incurred when using boundary mode.
◆
Setting the switch to peer-to-peer transparent mode differ with end-to-
end transparent mode only in the way it corrects and handles PTP
timing messages. Unlike the end-to-end clock, which corrects and
forwards all PTP timing messages, the peer-to-peer clock only corrects
and forwards Sync and Follow_Up messages. These messages are
updated for both the residence time of the Sync message and link delay
on the port receiving the Sync message.
◆
When PTP mode is set to boundary clock, the delay mechanism is
determined by the ptp delay-mechanism command. When set to
transparent clock, the delay mechanism is determined by message
exchanges with other clocks in the PTP domain.
E
XAMPLE
Console(config)#ptp mode boundary-clock
Console(config)#