ABB UniGear Series, Engineering Manual

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70 1VLG5 00007 E
Time synchronization schemes
Preferred schemes for HSR-PRP and PRP networks
The PRP redundancy protocol foresees that the grandmaster clock is doubly attached to both
LANs. An ordinary clock therefore receives the Sync (Follow-Up) and Announce messages
from each LAN independently. The ordinary clock treats each side as a different clock, but
does not apply the Best Master Clock algorithm since both have the same identity. Locating
two grandmaster clocks, one in each LAN also possible, in that case the doubly-attached
ordinary clocks execute the Best Master Clock algorithm to select the clock they are synchro-
nized to. However, singly attached nodes do not benefit from redundancy.
Figure 90: IEEE 1588 Time synchronization scheme for HSR-PRP networks
Figure 91: IEEE 1588 Time synchronization scheme for PRP networks