System Management
252
Basic System Configuration Guide
3HE 11010 AAAC TQZZA Edition: 01
− Ethernet multicast addressing is used for transmitting PTP messages. Both
the non-forwardable multicast address 01-80-C2-00-00-0E and forwardable
multicast address 01-1B-19-00-00-00 are supported.
− Virtual local area network (VLAN) tags within Ethernet frames carrying PTP
messages are not supported. When a PTP clock receives a PTP message
within a frame containing a VLAN tag, it discards this frame. A PTP clock
that is compliant with the profile described in Recommendation ITU-T
G.8275.1 must comply with IEEE 1588 – 2008 Annex F.
• Synchronization messages are sent at a rate of 16 packets/s; announce
messages are sent at a rate of 8 packets/s.
• On the 7705 SAR, the priority1 value is set to the default value (128) and cannot
be changed.
• On the 7705 SAR, if the clock-type parameter is set to ordinary slave, the
priority2 value is set to the default value (255) and cannot be changed.
For further details, refer to Recommendation ITU-T G.8275.1/Y.1369.1.
6.4.6.13.1 Synchronization Certainty/Uncertainty
As described in IEEE 1588v2 PTP, master clocks transmit Announce messages
containing the clock priority and quality. Each clock in the network can use the BMCA
and the clock properties received from the Announce messages to select the best
clock to synchronize to.
Within a PTP-aware network, there could be situations where boundary clocks
advertise clockClass 6 in the Announce message, which indicates that the parent
clock is connected to a traceable primary reference source/clock (PRS/PRC) in
locked mode (for example, locked to GNSS), and is therefore designated as the
synchronization time source. However, the PTP network may still be in a transient
state and stabilizing.
For example, this may occur when:
• a grand master clock locks and relocks to GNSS
• an intermediate boundary clock is started or restarted
• a new parent clock is chosen
Depending on the application, it may be important for a downstream boundary clock
or slave clock to know whether the PTP network has stabilized or is still
“synchronization uncertain”.
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