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| Basic Administration Protocols
C
14
HAPTER
PTP Configuration
time are not necessarily the same for all paths through the
switch or for successive messages crossing the same path.
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.
Peer-to-Peer – This method measures the delay required for
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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.
Setting the switch to peer-to-peer transparent mode differs 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.
Adjust – When this parameter is enabled, the switch will adjust the
◆
time of the local clock to match that of the master clock, based on
information in received Sync messages. (Default: Disabled)
When synchronization is enabled is thus enabled, the switch will
exchange PTP timing messages on the communication path to the
master clock. By exchanging Sync, Follow_Up, Delay_Req, and
Delay_Resp messages, the switch calculates the offset of the slave's
clock with respect to the master clock. It then adjusts the time reported
in the received Sync message, ensuring that the offset from the master
clock listed in the Current Data Set is now zero (see Show PTP
Information – Current Data).
Priority1 – Sets a preference level used by slave devices in selecting
◆
the master clock. Slave devices use the priority1 value when selecting a
master clock. (Range: 0-255; Default: 128)
Specify the Priority1 preference level to override the default criteria
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for best master clock selection. Lower values take precedence.
The best master clock algorithm (BMC), performs a distributed
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selection of the best candidate clock based on the following clock
properties.
Priority – An administratively assigned precedence hint used by
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the BMC to help select a grandmaster for the PTP domain.
Class – An attribute defining the clock's International Atomic
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Time (TAI) traceability.
Accuracy – An attribute defining the accuracy of the clock.
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– 596 –
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