The 7705 SAR supports IEC/IEEE 61850-9-3 and the C37.238-2017 extension, which are profiles that allow PTP to act as a timing source in power utility networks.
The IEC/IEEE 61850-9-3 and C37.238-2017 profiles support only Ethernet encapsulation with multicast addressing. Both profiles use the peer delay mechanism instead of the delay-request/response mechanism.
When configured for IEC/IEEE 61850-9-3 or C37.238-2017, the 7705 SAR can operate as a grand master clock, a boundary clock, or an ordinary slave clock and supports recovery of frequency as well as time of day/phase. Grand master clock functionality is only available for 7705 SAR variants with integrated GNSS.
Synchronous Ethernet can be used for frequency recovery as an optional mode for best time/phase recovery.
The IEC/IEEE 61850-9-3 and C37.238-2017 profiles have the following characteristics.
The default domain setting is 0 for IEC/IEEE 61850-9-3 and 254 for C37.238-2017; the allowed range is 0 to 255.
One-step clock operation is supported, without the need for follow-up messages.
When Ethernet encapsulation is used, 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.
Synchronization messages, Announce messages, and peer delay messages are sent, by default, at the rate of 1 packet/s.
By default, the priority1 and priority2 values are set to 255 when the clock type is ordinary slave and 128 when the clock type is ordinary master. The priority values can be configured to be between 0 and 255.
The C37.238-2017 profile uses the IEEE_C37_238 TLV in Announce messages between the parent and slave clocks. This TLV includes the grand master clock ID and the total time inaccuracy. Each clock in the chain adds its own inaccuracy to the total time inaccuracy, which gives the ultimate slave clock an estimate of the inaccuracy over the entire path.
The grand master inaccuracy includes the source time inaccuracy and the grand master time inaccuracy. When acting as a boundary clock, the system receives the total time inaccuracy from the parent clock and adds its own time inaccuracy, then sends out a TLV with the updated total time inaccuracy. By default, the time inaccuracy value is 100 ns for a grand master clock and 50 ns for a boundary clock. The default value can be changed for a boundary clock with the time-inaccuracy-override command.
For further details, see the IEC/IEEE 61850-9-3 standard and the C37.238-2017 extension.