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PTP Operational Overview
BMCA Operation
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PRISM MPI-MPX User Manual
BMCA Operation
The Best Master Clock Algorithm (BMCA) is used to choose the active master on the
domain. This is partially explained in the introduction to this document. The BMCA
operation varies somewhat as function of communication mode.
Multicast Mode
In Multicast mode, the active master sends announce messages which all other masters
and slaves can receive. So all devices can evaluate the BMCA and decide on the best
master. If any device detects that its BMCA rating is better than the current master, it
sends an announcement and takes over as the active master.
Unicast Mode
In Unicast mode, slaves only get Announce messages if they establish a grant from the
master. Therefore, each slave must set up a grant with every device in its AMT. Since the
masters do not set up grants from other masters, they do not have the information to
evaluate the BMCA and know if they are the active master. It is up to the slaves to
evaluate the BMCA based on the announce message they get from each master in their
AMT. Each slave then decides which master is the best and then set up grants for the
other message types. If slaves on a given network have a different list of masters in their
AMT, then they may choose a different master.
Mixed Mode
In a SMPTE ST2059 mixed environment, the announce message is Multicast. Therefore,
the BMCA can follow the Multicast conventions.