GE C70 Instruction Manual page 208

PRODUCT SETUP CHAPTER 5: SETTINGS
In a PTP system and in a PP system, the clocks automatically organize themselves into a master-slave synchronization
hierarchy with the "best" clock available making itself the "grandmaster" at the top of the hierarchy; all others make
themselves "slaves" and track the grandmaster. Typically the grandmaster clock receives its time from GPS satellites or
some other link to the international time standard. If the grandmaster fails, the next "best" clock available in the domain
assumes the grandmaster role. When a clock on start-up discovers that it is "better" than the present grandmaster, it
assumes the grandmaster role and the previous grandmaster reverts to slave.
Time messages issued by the grandmaster are delayed as they pass through the network both due to the finite speed of
the signal in the interconnecting fiber or wire, and due to processing delays in the Ethernet switches. Each clock and switch
implementing PP measures the propagation delay to each of its PP neighbors, and compensates for these delays in the
time received. Each network device implementing PP measures the processing delay it introduces in each time message
and compensates for this delay in the time it transmits. As a result, the time delivered to end-devices such as the UR are
virtually identical to the grandmaster time. If one of the network devices in the hierarchy does not fully implement PP, the
associated propagation delay and/or latency may not be compensated for, and the time received at the end-device can be
in error by more than 100 µs.
See the preceding Real Time Clock section for a description of when time values received via PTP are used to update the
relay's real time clock.
The following settings are available for configuring the relay for PTP. The PTP menu displays only when the option was
purchased.
— Power profile (IEEE Std C37.238 2011) requires that the relay only select a power profile compliant
STRICT POWER PROFILE
clock as a grandmaster, that the delivered time have worst-case error of ±1 µs, and that the peer delay mechanism be
implemented. With the strict power profile setting enabled, the relay only selects as master the clocks displaying the
IEEE_C37_238 identification codes. It uses a port only when the peer delay mechanism is operational. With the strict power
profile setting disabled, the relay uses clocks without the power profile identification when no power profile clocks are
present, and uses ports even if the peer delay mechanism is non-operational. This setting applies to all of the relay's PTP
5
capable ports.
— Set this setting to the domain number of the grandmaster-capable clock(s) to be synchronized to. A
PTP DOMAIN NUMBER
network can support multiple time distribution domains, each distinguished with a unique domain number. More
commonly, there is a single domain using the default domain number zero.
This setting applies to all of the relay's PTP capable ports.
— This setting selects the value of the priority field in the 802.1Q VLAN tag in request messages issued
PTP VLAN PRIORITY
by the relay's peer delay mechanism. In compliance with PP the default VLAN priority is 4, but it is recommended that it be
set to 7 in accordance with PTP. Depending on the characteristics of the device to which the relay is linked directly, VLAN
Priority can have no effect.
This setting applies to all of the relay's PTP capable ports.
— This setting selects the value of the ID field in the 802.1Q VLAN tag in request messages issued by the relay's
PTP VLAN ID
peer delay mechanism. It is provided in compliance with PP. As these messages have a destination address that indicates
they are not to be bridged, their VLAN ID serves no function, and so can be left at its default value. Depending on the
characteristics of the device to which the relay is linked directly, VLAN ID can have no effect. This setting applies to all of
the relay's PTP capable ports.
— While this port setting is selected to disabled, PTP is disabled on this port. The relay does not
PORT 1 ... 3 FUNCTION
generate or listen to PTP messages on this port.
— The time delivered by PTP is advanced by the time value in this setting prior to the time
PORT 1 ... 3 PATH DELAY ADDER
being used to synchronize the relay's real time clock. This is to compensate to the extent practical for time delivery delays
not compensated for in the network. In a fully compliant PP network, the peer delay and the processing delay mechanisms
compensate for all the delays between the grandmaster and the relay. In such networks, make this setting zero.
In networks containing one or more switches and/or clocks that do not implement both of these mechanisms, not all
delays are compensated, so the time of message arrival at the relay is later than the time indicated in the message. This
setting can be used to approximately compensate for this delay. However, as the relay is not aware of network switching
that dynamically changes the amount of uncompensated delay, there is no setting that always and completely corrects
for uncompensated delay. A setting can be chosen that reduces the worst-case error to half of the range between
minimum and maximum uncompensated delay, if these values are known.
5-84 C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL